Ch.4., Cell Structure

Question 1

A cell

Answer 1

A cell is the smallest unit of a living thing. Whether comprised of one cell (like bacteria) or many cells (like a human), we call it an organism. Thus, cells are the basic building blocks of all organisms.

Question 2

tissues.

Answer 2

Several cells of one kind that interconnect with each other and perform a shared function form tissues. These tissues combine to form an organ (your stomach, heart, or brain), and several organs comprise an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being). Here, we will examine the structure and function of cells.

Question 3

what type of cells are animal, plant, and bacterial respectively?

Answer 3

animal and plant = eukaryotic, bacterial = prokarytoic

Question 4

microscope and the images taken with it

Answer 4

Cells vary in size. With few exceptions, we cannot see individual cells with the naked eye, so scientists use microscopes (micro- = “small”; -scope = “to look at”) to study them. A microscope is an instrument that magnifies an object. We photograph most cells with a microscope, so we can call these images micrographs.

Question 5

how are images projected through the microscope

Answer 5

A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when one views through a microscope, and vice versa. Similarly, if one moves the slide left while looking through the microscope, it will appear to move right, and if one moves it down, it will seem to move up. This occurs because microscopes use two sets of lenses to magnify the image. Because of the manner by which light travels through the lenses, this two lens system produces an inverted image

Question 6

light microscopes (

Answer 6

Most student microscopes are light microscopes (Figure 4.2a). Visible light passes and bends through the lens system to enable the user to see the specimen. Light microscopes are advantageous for viewing living organisms, but since individual cells are generally transparent, their components are not distinguishable unless they are colored with special stains. Staining, however, usually kills the cells.

Question 7

Two parameters that are important in microscopy

Answer 7

magnification and resolving power. Magnification is the process of enlarging an object in appearance. Resolving power is the microscope’s ability to distinguish two adjacent structures as separate: the higher the resolution, the better the image’s clarity and detail. When one uses oil immersion lenses to study small objects, magnification usually increases to 1,000 times. In order to gain a better understanding of cellular structure and function, scientists typically use electron microscopes.

Question 8

electron microscopes

Answer 8

use a beam of electrons instead of a beam of light. Not only does this allow for higher magnification and, thus, more detail (Figure 4.3), it also provides higher resolving power. The method to prepare the specimen for viewing with an electron microscope kills the specimen. Electrons have short wavelengths (shorter than photons) that move best in a vacuum, so we cannot view living cells with an electron microscope.

Question 9

Restrictions of using an electron microscope

Answer 9

we cannot view living cells with an electron microscope.

Question 10

unified cell theory, who created it

Answer 10

By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory, which states that one or more cells comprise all living things, the cell is the basic unit of life, and new cells arise from existing cells.

Question 11

who coined the term cell, who discovered bacteria and protozoa

Answer 11

In the 1665 publication Micrographia, experimental scientist Robert Hooke coined the term “cell” for the box-like structures he observed when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa. Later advances in lenses, microscope construction, and staining techniques enabled other scientists to see some components inside cells.

Question 12

Cytotechnologists

Answer 12

Cytotechnologists (cyto- = “cell”) are professionals who study cells via microscopic examinations and other laboratory tests. They are trained to determine which cellular changes are within normal limits and which are abnormal. Their focus is not limited to cervical cells. They study cellular specimens that come from all organs. When they notice abnormalities, they consult a pathologist, a medical doctor who interprets and diagnoses changes that disease in body tissue and fluids cause.

Question 13

chharachetristics all cells have

Answer 13

All cells share four common components: 1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like cytosol within the cell in which there are other cellular components; 3) DNA, the cell’s genetic material; and 4) ribosomes, which synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.

Question 14

prokaryote

Answer 14

A prokaryote is a simple, mostly single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes.

Question 15

Where is Prokaryotic DNA

Answer 15

is in the cell’s central part: the nucleoid

Question 16

what kind opf cell wall and capsule do bacteria have and what are their functions?

Answer 16

Most bacteria have a peptidoglycan cell wall and many have a polysaccharide capsule
The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment.

Question 17

Flagellla, pili, fimbriae

Answer 17

fimbriae. Flagella are used for locomotion. Pili exchange genetic material during conjugation, the process by which one bacterium transfers genetic material to another through direct contact. Bacteria use fimbriae to attach to a host cell.

Question 18

bioremediation technologies.

Answer 18

Environmental microbiologists may look for new ways to use specially selected or genetically engineered microbes to remove pollutants from soil or groundwater, as well as hazardous elements from contaminated sites. We call using these microbes bioremediation technologies. Microbiologists can also work in the bioinformatics field, providing specialized knowledge and insight for designing, developing, and optimizing specificity of computer models of, for example, bacterial epidemics.

Question 19

prokarytic cell size and why this is advanatageous

Answer 19

At 0.1 to 5.0 μm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10 to 100 μm (Figure 4.6). The prokaryotes’ small size allows ions and organic molecules that enter them to quickly diffuse to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly diffuse.

Question 20

why is a small size nessecary for cells?

Answer 20

/3. Thus, as the radius of a cell increases, its surface area increases as the square of its radius, but its volume increases as the cube of its radius (much more rapidly). Therefore, as a cell increases in size, its surface area-to-volume ratio decreases.

Question 21

would the idea of the cell surface area inreasing as the square of its radius , but its volume increasing as the cube of its radius (more fast) hold true if it was a cube?

Answer 21

decreases. This same principle would apply if the cell had a cube shape (Figure 4.7).

Question 22

why is small size needed?

Answer 22

If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume. In other words, as a cell grows, it becomes less efficient. One way to become more efficient is to divide. Other ways are to increase surface area by foldings of the cell membrane, become flat or thin and elongated, or develop organelles that perform specific tasks. These adaptations lead to developing more sophisticated cells, which we call eukaryotic cells.

Question 23

charachteristics of eukaryotic cells

Answer 23

cells, eukaryotic cells have: 1) a membrane-bound nucleus; 2) numerous membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others; and 3) several, rod-shaped chromosomes.

Question 24

why do eukaryotic cells have a “true nucleaus?”

Answer 24

eukaryotic cells have: 1) a membrane-bound nucleus; 2) numerous membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others; and 3) several, rod-shaped chromosomes.

Question 25

peroxisome

Answer 25

houses oxidative metabolism: Peroxisomes are small, round organelles enclosed by single membranes. They carry out oxidation reactions that break down fatty acids and amino acids. They also detoxify many poisons that may enter the body. (Many of these oxidation reactions release hydrogen peroxide, H2O2, which would be damaging to cells; however, when these reactions are confined to peroxisomes, enzymes safely break down the H2O2 into oxygen and water.)

Question 26

a plasma membrane

Answer 26

Like prokaryotes, eukaryotic cells have a plasma membrane (Figure 4.9), a phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment. A phospholipid is a lipid molecule with two fatty acid chains and a phosphate-containing group. The plasma membrane controls the passage of organic molecules, ions, water, and oxygen into and out of the cell. Wastes (such as carbon dioxide and ammonia) also leave the cell by passing through the plasma membrane.

Question 27

glyco protein vs glycolipid

Answer 27

protien: protein with carbohydrate attached Glycolipid: lipid with carbohydrate attached

Question 28

microvilli

Answer 28

The plasma membranes of cells that specialize in absorption fold into fingerlike projections that we call microvilli (singular = microvillus); (Figure 4.10). Such cells typically line the small intestine, the organ that absorbs nutrients from digested food. This is an excellent example of form following function. People with celiac disease have an immune response to gluten, which is a protein in wheat, barley, and rye. The immune response damages microvilli, and thus, afflicted individuals cannot absorb nutrients.

Question 29

cytoplasm; consistency

Answer 29

The cytoplasm is the cell's entire region between the plasma membrane and the nuclear envelope (a structure we will discuss shortly). It is comprised of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals (Figure 4.8). Even though the cytoplasm consists of 70 to 80 percent water, it has a semi-solid consistency, which comes from the proteins within it. However, proteins are not the only organic molecules in the cytoplasm.

Question 30

nuclear envelope

Answer 30

is a double-membrane structure that constitutes the nucleus' outermost portion (Figure 4.11). Both the nuclear envelope's inner and outer membranes are phospholipid bilayers.

Question 31

nucleoplasm

Answer 31

is the semi-solid fluid inside the nucleus, where we find the chromatin and the nucleolus.

Question 32

chromosomes

Answer 32

To understand chromatin, it is helpful to first explore chromosomes, structures within the nucleus that are made up of DNA, the hereditary material.

Question 33

structure of chromosomes in prokaryotes vs eukaryotes

Answer 33

You may remember that in prokaryotes, DNA is organized into a single circular chromosome. In eukaryotes, chromosomes are linear structures. Every eukaryotic species has a specific number of chromosomes in the nucleus of each cell.

Question 34

chromatin

Answer 34

When the cell is in the growth and maintenance phases of its life cycle, proteins attach to chromosomes, and they resemble an unwound, jumbled bunch of threads. We call these unwound protein-chromosome complexes chromatin

Question 35

The Nucleolus

Answer 35

We already know that the nucleus directs the synthesis of ribosomes, but how does it do this? Some chromosomes have sections of DNA that encode ribosomal RNA. A darkly staining area within the nucleus called the nucleolus (plural = nucleoli) aggregates the ribosomal RNA with associated proteins to assemble the ribosomal subunits that are then transported out through the pores in the nuclear envelope to the cytoplasm.

Question 36

Ribosomes

Answer 36

Ribosomes are the cellular structures responsible for protein synthesis. When we view them through an electron microscope, ribosomes appear either as clusters (polyribosomes) or single, tiny dots that float freely in the cytoplasm.

Question 37

two subunits of ribosomes

Answer 37

Electron microscopy shows us that ribosomes, which are large protein and RNA complexes, consist of two subunits, large and small

Question 38

mRna

Answer 38

Ribosomes receive their “orders” for protein synthesis from the nucleus where the DNA transcribes into messenger RNA (mRNA). The mRNA travels to the ribosomes, which translate the code provided by the sequence of the nitrogenous bases in the mRNA into a specific order of amino acids in a protein. Amino acids are the building blocks of proteins.

Question 39

Mitochondria

Answer 39

Scientists often call mitochondria (singular = mitochondrion) “powerhouses” or “energy factories” of both plant and animal cells because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule.

Question 40

ATP

Answer 40

represents the cell's short-term stored energy.

Question 41

Cellular respiration

Answer 41

respiration is the process of making ATP using the chemical energy in glucose and other nutrients. In mitochondria, this process uses oxygen and produces carbon dioxide as a waste product. In fact, the carbon dioxide that you exhale with every breath comes from the cellular reactions that produce carbon dioxide as a byproduct.

Question 42

which type of cells have a very high mitochondria concentration?

Answer 42

In keeping with our theme of form following function, it is important to point out that muscle cells have a very high concentration of mitochondria that produce ATP. Your muscle cells need considerable energy to keep your body moving. When your cells don’t get enough oxygen, they do not make much ATP. Instead, producing lactic acid accompanies the small amount of ATP they make in the absence of oxygen.

Question 43

structure/charachteristics of mitchondria

Answer 43

Mitochondria are oval-shaped, double membrane organelles (Figure 4.14) that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded with proteins. The inner layer has folds called cristae. We call the area surrounded by the folds the mitochondrial matrix. The cristae and the matrix have different roles in cellular respiration.

Question 44

peroxisomes/alcohol processing

Answer 44

Peroxisomes are small, round organelles enclosed by single membranes. They carry out oxidation reactions that break down fatty acids and amino acids. They also detoxify many poisons that may enter the body. (Many of these oxidation reactions release hydrogen peroxide, H2O2, which would be damaging to cells; however, when these reactions are confined to peroxisomes, enzymes safely break down the H2O2 into oxygen and water.) For example, peroxisomes in liver cells detoxify alcohol.

Question 45

Glyoxysomes

Answer 45

which are specialized peroxisomes in plants, are responsible for converting stored fats into sugars. Plant cells contain many different types of peroxisomes that play a role in metabolism, pathogene defense, and stress response, to mention a few.

Question 46

Vesicles and vacuoles

Answer 46

Vesicles and vacuoles are membrane-bound sacs that function in storage and transport. Other than the fact that vacuoles are somewhat larger than vesicles, there is a very subtle distinction between them. Vesicle membranes can fuse with either the plasma membrane or other membrane systems within the cell. Additionally, some agents such as enzymes within plant vacuoles break down macromolecules. The vacuole's membrane does not fuse with the membranes of other cellular components.

Question 47

Animal Cells versus Plant Cells

Answer 47

cells. While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC: a complex we call the centrosome. Animal cells each have a centrosome and lysosomes; whereas, most plant cells do not. Plant cells have a cell wall, chloroplasts and other specialized plastids, and a large central vacuole; whereas, animal cells do not.

Question 48

centrosome

Answer 48

The centrosome is a microtubule-organizing center found near the nuclei of animal cells. It contains a pair of centrioles, two structures that lie perpendicular to each other (Figure 4.15). Each centriole is a cylinder of nine triplets of microtubules.

Question 49

why is the centriole's function in cell division not clear?

Answer 49

The centrosome (the organelle where all microtubules originate) replicates itself before a cell divides, and the centrioles appear to have some role in pulling the duplicated chromosomes to opposite ends of the dividing cell. However, the centriole's exact function in cell division isn’t clear, because cells that have had the centrosome removed can still divide, and plant cells, which lack centrosomes, are capable of cell division.

Question 50

lysosomes and pH

Answer 50

Animal cells have another set of organelles that most plant cells do not: lysosomes. The lysosomes are the cell’s “garbage disposal.” In plant cells, the digestive processes take place in vacuoles. Enzymes within the lysosomes aid in breaking down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles. These enzymes are active at a much lower pH than the cytoplasm's. Therefore, the pH within lysosomes is more acidic than the cytoplasm's pH. Many reactions that take place in the cytoplasm could not occur at a low pH, so again, the advantage of compartmentalizing the eukaryotic cell into organelles is apparent.

Question 51

prokaryotic cell walls' chief component is

Answer 51

is peptidoglycan,

Question 52

the major organic molecule in the plant (and some protists') cell wall

Answer 52

cell wall is cellulose a polysaccharide comprised of glucose units.

Question 53

Chloroplasts

Answer 53

Like the mitochondria, chloroplasts have their own DNA and ribosomes, but chloroplasts have an entirely different function. Chloroplasts are plant cell organelles that carry out photosynthesis.

Question 54

autotrophs vs heteroautrophs

Answer 54

Photosynthesis is the series of reactions that use carbon dioxide, water, and light energy to make glucose and oxygen. This is a major difference between plants and animals. Plants (autotrophs) are able to make their own food, like sugars used in cellular respiration to provide ATP energy generated in the plant mitochondria. Animals (heterotrophs) must ingest their food.

Question 55

thylakoids

Answer 55

Like mitochondria, chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplast’s inner membrane is a set of interconnected and stacked fluid-filled membrane sacs we call thylakoids

Question 56

granum and stroma

Answer 56

Each thylakoid stack is a granum (plural = grana). We call the fluid enclosed by the inner membrane that surrounds the grana the stroma.

Question 57

chlorophyll,

Answer 57

The chloroplasts contain a green pigment, chlorophyll, which captures the light energy that drives the reactions of photosynthesis. Like plant cells, photosynthetic protists also have chloroplasts. Some bacteria perform photosynthesis, but their chlorophyll is not relegated to an organelle.

Question 58

Endosymbiosis

Answer 58

Symbiosis is any type of close and long term relationship between two organisms from different species depend on each other for their survival. In some cases both organisms benefit from the relationship. Endosymbiosis (endo- = “within”) is a mutually beneficial relationship in which one organism lives inside the other. Endosymbiotic relationships abound in nature. We have already mentioned that microbes that produce vitamin K live inside the human gut. This relationship is beneficial for us because we are unable to synthesize vitamin K. It is also beneficial for the microbes because they are protected from other organisms and from drying out, and they receive abundant food from the environment of the large intestine.

Question 59

evolutionary role of endosymbiosis

Answer 59

Scientists have long noticed that bacteria, mitochondria, and chloroplasts are similar in size. We also know that bacteria have DNA and ribosomes, just like mitochondria and chloroplasts. Scientists believe that host cells and bacteria formed an endosymbiotic relationship when the host cells ingested both aerobic and autotrophic bacteria (cyanobacteria) but did not destroy them. Through many millions of years of evolution, these ingested bacteria became more specialized in their functions, with the aerobic bacteria becoming mitochondria and the autotrophic bacteria becoming chloroplasts.

Question 60

central vacuole plays

Answer 60

Previously, we mentioned vacuoles as essential components of plant cells. If you look at Figure 4.8b, you will see that plant cells each have a large central vacuole that occupies most of the cell's volume. The central vacuole plays a key role in regulating the cell’s concentration of water in changing environmental conditions. Have you ever noticed that if you forget to water a plant for a few days, it wilts? That’s because as the water concentration in the soil becomes lower than the water concentration in the plant, water moves out of the central vacuoles and cytoplasm. As the central vacuole shrinks, it leaves the cell wall unsupported. This loss of support to the plant's cell walls results in the wilted appearance.

Question 61

central vacuole and cell expansion

Answer 61

The central vacuole also supports the cell's expansion. When the central vacuole holds more water, the cell becomes larger without having to invest considerable energy in synthesizing new cytoplasm.

Question 62

endomembrane system

Answer 62

The endomembrane system (endo = “within”) is a group of membranes and organelles (Figure 4.18) in eukaryotic cells that works together to modify, package, and transport lipids and proteins.

Question 63

What is included in the endomembrane system?

Answer 63

nuclear envelope lysosomes vesicles endoplasmic reticulum golgi apparatus

Question 64

why is the plasma membrane still included in the endomembrane system, even though it is not technically within the cell?

Answer 64

Although not technically within the cell, the plasma membrane is included in the endomembrane system because, as you will see, it interacts with the other endomembranous organelles. The endomembrane system does not include either mitochondria or chloroplast membranes.

Question 65

endoplasmic reticulum (ER)

Answer 65

The endoplasmic reticulum (ER) (Figure 4.18) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesizes lipids. However, these two functions take place in separate areas of the ER: the rough ER and the smooth ER, respectively.

Question 66

lumen/cisternal space

Answer 66

We call the ER tubules' hollow portion the lumen or cisternal space. The ER's membrane, which is a phospholipid bilayer embedded with proteins, is continuous with the nuclear envelope.

Question 67

rough endoplasmic reticulum (RER)

Answer 67

Scientists have named the rough endoplasmic reticulum (RER) as such because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewing it through an electron microscope

Question 68

RER's lumen

Answer 68

Ribosomes transfer their newly synthesized proteins into the RER's lumen where they undergo structural modifications, such as folding or a These modified proteins incorporate into cellular membranes—the ER or the ER's or other organelles' membranes. The proteins can also secrete from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.cquiring side chains.

Question 69

transport vesicles

Answer 69

If the phospholipids or modified proteins are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER’s membrane

Question 70

smooth endoplasmic reticulum (SER)

Answer 70

The smooth endoplasmic reticulum (SER) is continuous with the RER but has few or no ribosomes on its cytoplasmic surface (Figure 4.18). SER functions include synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storing calcium ions.

Question 71

the sarcoplasmic reticulum,

Answer 71

In muscle cells, a specialized SER, the sarcoplasmic reticulum, is responsible for storing calcium ions that are needed to trigger the muscle cells' coordinated contractions.

Question 72

Golgi apparatus

Answer 72

Before reaching their final destination, the lipids or proteins within the transport vesicles still need sorting, packaging, and tagging so that they end up in the right place. Sorting, tagging, packaging, and distributing lipids and proteins takes place in the Golgi apparatus (also called the Golgi body), a series of flattened membranous sacs

Question 73

The side of the Golgi apparatus that is closer to the ER

Answer 73

cis face.

Question 74

The side of the Golgi apparatus that is The opposite side of the ER

Answer 74

The opposite side is the trans face.

Question 75

what is the most frequent modification carried out by the golgi apparatus?

Answer 75

As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted. The most frequent modification is adding short sugar molecule chains. These newly modified proteins and lipids then tag with phosphate groups or other small molecules in order to travel to their proper destinations.

Question 76

what happens after oproteins are modified and tagged in the golgi apparatus?

Answer 76

Finally, the modified and tagged proteins are packaged into secretory vesicles that bud from the Golgi's trans face. While some of these vesicles deposit their contents into other cell parts where they will be used, other secretory vesicles fuse with the plasma membrane and release their contents outside the cell.

Question 77

which cells have an abundance of Golgi?

Answer 77

In another example of form following function, cells that engage in a great deal of secretory activity (such as salivary gland cells that secrete digestive enzymes or immune system cells that secrete antibodies) have an abundance of Golgi.

Question 78

Lowe disease.

Answer 78

One such disease is Lowe disease (or oculocerebrorenal syndrome, because it affects the eyes, brain, and kidneys). In Lowe disease, there is a deficiency in an enzyme localized to the Golgi apparatus. Children with Lowe disease are born with cataracts, typically develop kidney disease after the first year of life, and may have intellectual disabilities.

Question 79

What causes Lowe disease?

Answer 79

A mutation on the X chromosome causes Lowe disease. The X chromosome is one of the two human sex chromosomes, as these chromosomes determine a person's sex. Females possess two X chromosomes while males possess one X and one Y chromosome. In females, the genes on only one of the two X chromosomes are expressed. Females who carry the Lowe disease gene on one of their X chromosomes are carriers and do not show symptoms of the disease. However, males only have one X chromosome and the genes on this chromosome are always expressed. Therefore, males will always have Lowe disease if their X chromosome carries the Lowe disease gene.

Question 80

Lysosomes

Answer 80

cells, lysosomes are part of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell.

Question 81

phagocytosis or endocytosis,

Answer 81

A good example of this occurs in macrophages, a group of white blood cells which are part of your body’s immune system. In a process that scientists call phagocytosis or endocytosis, a section of the macrophage's plasma membrane invaginates (folds in) and engulfs a pathogen.

Question 82

hoow does phagocytosis destroy a pathogern with the lysosomes?

Answer 82

The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome. The lysosome’s hydrolytic enzymes then destroy the pathogen

Question 83

cytoskeleton

Question 84

If you were to remove all the organelles from a cell, would the plasma membrane and the cytoplasm be the only components left?

Answer 84

No. Within the cytoplasm, there would still be ions and organic molecules, plus a network of protein fibers that help maintain the cell's shape, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable cells within multicellular organisms to move. Collectively, scientists call this network of protein fibers the cytoskeleton

Question 85

There are three types of fibers within the cytoskeleton:

Answer 85

microfilaments, intermediate filaments, and microtubules

Question 86

Microfilaments

Answer 86

Of the three types of protein fibers in the cytoskeleton, microfilaments are the narrowest. They function in cellular movement, have a diameter of about 7 nm, and are comprised of two globular protein intertwined strands, which we call actin (Figure 4.23). For this reason, we also call microfilaments actin filaments.

Question 87

why are microfilaments also called actin filaments?

Answer 87

Of the three types of protein fibers in the cytoskeleton, microfilaments are the narrowest. They function in cellular movement, have a diameter of about 7 nm, and are comprised of two globular protein intertwined strands, which we call actin (Figure 4.23). For this reason, we also call microfilaments actin filaments.

Question 88

What powers actin to assemble its filamentous form?

Answer 88

ATP powers actin to assemble its filamentous form, which serves as a track for the movement of a motor protein we call myosin. This enables actin to engage in cellular events requiring motion, such as cell division in eukaryotic cells and cytoplasmic streaming, which is the cell cytoplasm's circular movement in plant cells.

Question 89

What causes muscle contraction?

Answer 89

When your actin and myosin filaments slide past each other, your muscles contract.

Question 90

Other functions of microfilamentss

Answer 90

Microfilaments also provide some rigidity and shape to the cell. They can depolymerize (disassemble) and reform quickly, thus enabling a cell to change its shape and move. White blood cells (your body’s infection-fighting cells) make good use of this ability. They can move to an infection site and phagocytize the pathogen.

Question 91

cytoskeleton intermediate Filaments

Answer 91

Several strands of fibrous proteins that are wound together comprise intermediate filaments (Figure 4.24). Cytoskeleton elements get their name from the fact that their diameter, 8 to 10 nm, is between those of microfilaments and microtubules.

Question 92

Role of intermediate filaments

Answer 92

Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the cell's shape, and anchor the nucleus and other organelles in place. Figure 4.22 shows how intermediate filaments create a supportive scaffolding inside the cell. The intermediate filaments are the most diverse group of cytoskeletal elements. Several fibrous protein types are in the intermediate filaments. You are probably most familiar with keratin, the fibrous protein that strengthens your hair, nails, and the skin's epidermis.

Question 93

Microtubules

Answer 93

microtubules are small hollow tubes.

Question 94

Widest components of the cytoskeleton and their function

Answer 94

With a diameter of about 25 nm, microtubules are cytoskeletons' widest components. They help the cell resist compression, provide a track along which vesicles move through the cell, and pull replicated chromosomes to opposite ends of a dividing cell. Like microfilaments, microtubules can disassemble and reform quickly.

Question 94

What makes up the microtubule's walls?

Answer 94

Polymerized dimers of α-tubulin and β-tubulin, two globular proteins, comprise the microtubule's walls (

Question 95

What are the structural elements of flaagella, cilia, and cnetrioles?

Answer 95

Microtubules are also the structural elements of flagella, cilia, and centrioles

Question 96

What organizes microtubules in animal cells?

Answer 96

bodies). In animal cells, the centrosome is the microtubule-organizing center.

Question 97

Flagella

Answer 97

The flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and enable an entire cell to move (for example, sperm, Euglena, and some prokaryotes).

Question 98

cilia (singular = cilium)

Answer 98

many of them extend along the plasma membrane's entire surface. They are short, hair-like structures that move entire cells (such as paramecia) or substances along the cell's outer surface (for example, the cilia of cells lining the Fallopian tubes that move the ovum toward the uterus, or cilia lining the cells of the respiratory tract that trap particulate matter and move it toward your nostrils.)

Question 99

a “9 + 2 array.”

Answer 99

Despite their differences in length and number, flagella and cilia share a common structural arrangement of microtubules called a “9 + 2 array.” This is an appropriate name because a single flagellum or cilium is made of a ring of nine microtubule doublets, surrounding a single microtubule doublet in the center

Question 100

Where do most cells in mutlicellular organisms release materials to, and what are they releasing?

Answer 100

While cells in most multicellular organisms release materials into the extracellular space: The primary components of these materials are proteins, and the most abundant protein is collagen.

Question 101

the extracellular matrix

Answer 101

collagen. Collagen fibers are interwoven with proteoglycans, which are carbohydrate-containing protein molecules. Collectively, we call these materials the extracellular matrix (Figure 4.27). Not only does the extracellular matrix hold the cells together to form a tissue, but it also allows the cells within the tissue to communicate with each other.

Question 102

Not only does the extracellular matrix hold the cells together to form a tissue, but it also allows the cells within the tissue to communicate with each other. How can this happen?

Answer 102

Cells have protein receptors on their plasma membranes' extracellular surfaces. 1. When a molecule within the matrix binds to the receptor, it changes the receptor's molecular structure. 2. The receptor, in turn, changes the microfilaments' conformation positioned just inside the plasma membrane. =These conformational changes induce chemical signals inside the cell that reach the nucleus 4. turn “on” or “off” the transcription of specific DNA sections, which affects the associated protein production, thus changing the activities within the cell.

Question 103

Blood clotting example of the extracellular matrix's role in cell communication.

Answer 103

1. When the cells lining a blood vessel are damaged, they display a protein receptor, which we call tissue factor. 2. When tissue factor binds with another factor in the extracellular matrix, it causes platelets to adhere to the damaged blood vessel's wall 3. stimulates the adjacent smooth muscle cells in the blood vessel to contract (thus constricting the blood vessel) 4. initiates a series of steps that stimulate the platelets to produce clotting factors.

Question 104

intercellular junctions, plant vs animal cells

Answer 104

Cells can also communicate with each other via direct contact, or intercellular junctions. There are differences in the ways that plant and animal and fungal cells communicate. Plasmodesmata are junctions between plant cells; whereas, animal cell contacts include tight junctions, gap junctions, and desmosomes.

Question 105

In general, long stretches of the plasma membranes of neighboring plant cells cannot touch one another because the cell wall that surrounds each cell separates them (Figure 4.8). How then, can a plant transfer water and other soil nutrients from its roots, through its stems, and to its leaves?

Answer 105

Such transport uses the vascular tissues (xylem and phloem) primarily. There also exist structural modifications, which we call plasmodesmata (singular = plasmodesma). Numerous channels that pass between adjacent plant cells' cell walls connect their cytoplasm, and enable transport of materials from cell to cell, and thus throughout the plant

Question 106

tight junction

Answer 106

A tight junction is a watertight seal between two adjacent animal cells (Figure 4.29). Proteins (predominantly two proteins called claudins and occludins) tightly hold the cells against each other.

Question 107

the tight junctions of the epithelial cells lining your urinary bladder

Answer 107

This tight adherence prevents materials from leaking between the cells; tight junctions are typically found in epithelial tissues that line internal organs and cavities, and comprise most of the skin. For example, the tight junctions of the epithelial cells lining your urinary bladder prevent urine from leaking out into the extracellular space.

Question 108

desmosomes

Answer 108

Also only in animal cells are desmosomes, which act like spot welds between adjacent epithelial cells

Question 109

Cadherins,

Answer 109

Cadherins, short proteins in the plasma membrane connect to intermediate filaments to create desmosomes. The cadherins connect two adjacent cells and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles. The cadherins connect two adjacent cells and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles.

Question 110

Gap junctions and similarity to plasmodesmata in plant cells

Answer 110

Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow for transporting ions, nutrients, and other substances that enable cells to communicate

Question 111

how are gap junctions formed, and why are they important for heart muscle contraction?

Answer 111

when a set of six proteins (connexins) in the plasma membrane arrange themselves in an elongated donut-like configuration - a connexon. When the connexon's pores (“doughnut holes”) in adjacent animal cells align, a channel between the two cells forms. Gap junctions are particularly important in cardiac muscle. The electrical signal for the muscle to contract passes efficiently through gap junctions, allowing the heart muscle cells to contract in tandem.