cell structure- chapter 3

Question 1

what is the magnification equation

Answer 1

size of image/size of real object

Question 2

what is the resolution

Answer 2

the minimum distance apart that two objects can be in order for them to appear as separate items

Question 3

what is cell fractionation

Answer 3

the process where cells are broken up and the different organelles that they contain are separated out

Question 4

before cell fractionation, why is the tissue placed in a cold buffered solution of the same water potential as the tissue

Answer 4

cold= reduce enzyme activity that might break down the organelles

same water potential= prevent organelles bursting or shrinking as a result of osmotic gain or loss of water

buffered= so the pH doesn’t fluctuate, as any change in pH could alter the structure of organelles or affect the functioning enzymes

Question 5

what are the two stages to cell fractionation and explain them

Answer 5

homogenation= cells are broken up by a homogeniser (blender) which releases the organelles from the cell. the resultant fluid, known as homogenate, is then filtered to remove any complete cells and large pieces of debris

ultracentrifugation= process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speeds in order to create a centrifugal forces

Question 6

what is the process of ultracentrifugation of animal cells

Answer 6

• the tube of filtrate is placed in the centrifuge and spun at a slow speed
• the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet
• the fluid at the top of the tube (supernatant) is removed, leaving the sediment of the nuclei
• the supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
• the next heaviest organelles, the mitochondria, are forced to the bottom of the tube
• the process is continued this way so that, at each increase in speed, the next heaviest organelle is sedimented and separated out

Question 7

what are two advantages of the electron microscope

Answer 7

• the electron beam has a very short wavelength and the microscope can therefore resolve objects as well- high resolving power
• as electrons are negatively charged the beam can be focused using electromagnets

Question 8

what are the two types of electron microscope

Answer 8

TEM (transmission electron microscope) and SEM (scanning electron microscope)

Question 9

what is a TEM microscope

Answer 9

• consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet
• the beam passes through a thin section of the specimen
• parts of the specimen absorb electrons and therefore appear darker
• other parts allow electrons to pass through and so appear bright
• an image is produced on a screen and this can be photographed to give a photomicrograph

Question 10

why cant the resolving power of the TEM is 0.1nm always be achieved

Answer 10

• difficulties preparing the specimen limit the resolution that can be achieved
• a higher energy electron beam is required and this may destroy the specimen

Question 11

what are the main limitations of TEM

Answer 11

• the whole system must be in a vacuum and therefore living specimens cannot be observed
• a complex ‘staining’ process is required and even then the image is not in colour
• the specimen must be extremely thing
• the image may contain artefacts- theyre things that result from the way the specimen is prepared, artefacts may appear on the finished photomicrograph but are not part of the natural specimen

Question 12

what are the limitations of an SEM

Answer 12

all the same as TEM except that the specimens need to not be extremely thin as electrons do no penetrate

Question 13

explain an SEM

Answer 13

• directs a beam of electrons on to the surface of the specimen from above, rather than penetrating it from below
• the beam is then passed back and forth across a portion of the specimen in a regular pattern
• the electrons are scattered by the specimen and the pattern of this scattering depends on the contours of the specimen surface
• you can build up a 3-D image by computer analysis of the pattern of scattered electrons and secondary electrons produces
• the basic SEM had a lower resolving power than a TEM

Question 14

what is an eyepiece graticule

Answer 14

• can measure the size of objects
• the graticule is a glass disc that is placed in the eyepiece of a microscope
• a scale is etched on the glass disc

Question 15

what is a stage micrometer

Answer 15

needed to calibrate an eyepiece graticule

Question 16

what does the nucleus contain

Answer 16

the hereditary material and controls the cells activities

Question 17

what are 5 structures in the nucleus

Answer 17

nuclear envelope, nuclear pores, nucleoplasm, chromosomes and nucleolus

Question 18

what does the nuclear envelope do

Answer 18

• is a double membrane that surrounds the nucleus
  -Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface
• It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it

Question 19

what do the nuclear pores do

Answer 19

• allow the passage of large molecules, such as messenger RNA, out of the nucleus
• There are typically around 3000 pores in each nucleus

Question 20

what is the nucleoplasm do

Answer 20

the granular, jelly-like material that makes up the bulk of the nucleus

Question 21

what are the chromosomes in the nucleus

Answer 21

consists of protein-bound, linear DNA

Question 22

what is the nucleolus

Answer 22

• a small spherical region within the nucleoplasm
• It manufactures ribosomal RNA and assembles the ribosomes
• There may be more than one nucleolus in a nucleus.

Question 23

what are the 3 functions of the nucleus

Answer 23

• act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
• retain the genetic material of the cell in the form of DNA and chromosomes
• manufacture ribosomal RNA and ribosomes

Question 24

what structures are within the mitochondrion

Answer 24

double membrane
cristae
matrix

Question 25

what is the double membrane of the mitochondria

Answer 25

controls the entry and exit of material inner of the two is folded to form extensions known as cristae

Question 26

what is the cristae

Answer 26

- extensions of the inner membrane, which in some species extend across the whole width of the mitochondrion - These provide a large surface area for the attachment of enzymes and other proteins involved in respiration

Question 27

what is the matrix

Answer 27

- makes up the remainder of the mitochondrion - It contains protein, lipids, ribosomes and DNA that allows the mitochondria to control the production of some their own proteins - Many enzymes involved in respiration are found in the matrix

Question 28

explain what the mitochondrias do

Answer 28

- the sites of the aerobic stages of respiration (the Krebs cycle and the oxidative phosphorylation pathway). -they are responsible for the production of the energy-carrier molecule, ATP, from respiratory substrates such as glucose - Because of this, the number and size of the mitochondria, and the number of their cristae, are high in cells that have a high level of metabolic activity and therefore require a plentiful supply of ATP - Examples of metabolically active cells include muscle and epithelial cells; cells in the intestines require a lot of ATP in the process of absorbing substances from the intestines by active transport

Question 29

what are chloroplasts

Answer 29

the organelles that carry out photosynthesis

Question 30

what structures does the chloroplast have

Answer 30

chloroplast envelope grana thylakoids chlorophyll stroma

Question 31

what is the chloroplast envelope

Answer 31

- a double plasma membrane that surrounds the organelle -It is highly selective in what it allows to enter and leave the chloroplast

Question 32

what is the grana

Answer 32

- are stacks of up to 100 disc-like structures called thylakoids - within the thylakoids is the photosynthetic pigment called chlorophyll - Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana - The grana are where the first stage of photosynthesis (light absorption) takes place

Question 33

what is the stroma

Answer 33

- a fluid-filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place - Within the stroma are a number of other structures, such as starch grains

Question 34

how are chloroplasts adapted to their function of harvesting sunlight and carrying out photosynthesis

Answer 34

- The granal membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. These chemicals are attached to the membrane in a highly ordered fashion - The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis - Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesi

Question 35

what is the endoplasmic reticulum

Answer 35

- 3D system of sheet-like membranes, spreading through the cytoplasm of the cells - It is continuous with the outer nuclear membrane -The membranes enclose a network of tubules and flattened sacs called cisternae - There are two types (RER, SER)

Question 36

what is the RER and its functions

Answer 36

- has ribosomes present on the outer surfaces of the membranes 1. provide a large surface area for the synthesis of proteins and glycoproteins 2. provide a pathway for the transport of materials, especially proteins, throughout the cell.

Question 37

what is the SER and its functions

Answer 37

- lacks ribosomes on its surface and is often more tubular in appearance 1. synthesise, store and transport lipids 2. synthesise, store and transport carbohydrates

Question 38

what are the functions of the golgi apparatus

Answer 38

- add carbohydrate to proteins to form glycoproteins - produce secretory enzymes, such as those secreted by the pancreas - secrete carbohydrates, such as those used in making cell walls in plants - transport, modify and store lipids - form lysosomes

Question 39

what is the golgi apparatus and explain what it does

Answer 39

- in almost all eukaryotic cells - consists of a stack of membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles - the proteins and lipids produced by the ER are passed through the Golgi in strict sequence. - Golgi modifies these proteins often adding non-protein components, such as carbohydrate, to them - ‘labels’ them, allowing them to be accurately sorted and sent to their correct destinations - Once sorted, the modified proteins and lipids are transported in Golgi vesicles which are regularly pinched off from the ends of the Golgi cisternae - These vesicles may move to the cell surface, where they fuse with the membrane and release their contents to the outside

Question 40

what are the functions of lysosomes

Answer 40

-hydrolyse material ingested by phagocytic cells, such as white blood cells and bacteria - release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell - digest worn out organelles so that the useful chemicals they are made of can be re-used - completely break down cells after they have died (autolysis).

Question 41

what are lysosomes

Answer 41

- formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases -contain lysozymes, enzymes that hydrolyse the cell walls of certain bacteria - As many as 50 such enzymes may be contained in a single lysosome - lysosomes isolate these enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell

Question 42

what are ribosomes

Answer 42

- small cytoplasmic granules found in all cells -they may occur in the cytoplasm or be associated with the RER - there are two types, depending on the cells in which they are found: 1. 80S 2. 70S

Question 43

what is the cell wall

Answer 43

-characteristic of all plant cells, the cell wall consists of microfibrils of the polysaccharide cellulose, embedded in a matrix - Cellulose microfibrils have considerable strength and so contribute to the overall strength of the cell wall.

Question 44

what are 2 features of the cell wal

Answer 44

-They consist of a number of polysaccharides, such as cellulose - There is a thin layer, called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together

Question 45

what are the functions of the cell wall

Answer 45

- to provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water -to give mechanical strength to the plant as a whole -to allow water to pass along it and so contribute to the movement of water through the plant.

Question 46

what are the cell walls of algae made up of what are the cell walls of fungi made up of

Answer 46

cellulose or glycoproteins, or a mixture chitin

Question 47

what are the functions of plant vacuoles

Answer 47

- They support herbaceous plants, and herbaceous parts of woody plants, by making cells turgid - The sugars and amino acids may act as a temporary food store -The pigments may colour petals to attract pollinating insects

Question 48

what is the vacuole

Answer 48

-A fluid-filled sac bounded by a single membrane may be termed a vacuole -The single membrane around it is called the tonoplast. -A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins

Question 49

what does mitosis produce what does meiosis produce

Answer 49

two daughter cells that have the same number of chromosomes as the parent cell produces four daughter cells, each with half the number of chromosomes of the parent cell

Question 50

what is mitosis always preceded by (and describe)

Answer 50

interphase - period of considerable cellular activity that includes a very important event, the replication of DNA - The two copies of DNA after replication remain joined at a place called the centromere

Question 51

what are the 4 stages of mitosis

Answer 51

prophase, metaphase, anaphase, telophase and cytokinesis

Question 52

what happens in prophase

Answer 52

- the chromosomes first become visible, initially as long thin threads, which later shorten and thicken -Animal cells contain two cylindrical organelles called centrioles, each of which moves to opposite ends (called poles) of the cell - From each of the centrioles, spindle fibres develop, which span the cell from pole to pole - Collectively, these spindle fibres are called the spindle apparatus - The nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm of the cell - These chromosomes are drawn towards the equator of the cell by the spindle fibres attached to the centromere

Question 53

what happens in metaphase

Answer 53

- the chromosomes are seen to be made up of two chromatids - each chromatid is an identical copy of DNA from the parent cell - The chromatids are joined by the centromere - It is to this centromere that some microtubules from the poles are attached, and the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell

Question 54

what happens in anaphase

Answer 54

- the centromeres divide into two and the spindle fibres pull the individual chromatids making up the chromosome apart - The chromatids move rapidly to their respective, opposite poles of the cell and we now refer to them as chromosomes - The energy for the process is provided by mitochondria, which gather around the spindle fibres - If cells are treated with chemicals that destroy the spindle, the chromosomes remain at the equator, unable to reach the poles

Question 55

what happens in telophase and cytokinesis

Answer 55

- the chromosomes reach their respective poles and become longer and thinner, finally disappearing altogether, leaving only widely spread chromatin - The spindle fibres disintegrate and the nuclear envelope and nucleolus re-form - Finally the cytoplasm divides in a process called cytokinesis

Question 56

what is binary fission

Answer 56

- cell division in prokaryotic cells 1. circular DNA molecule replicates and both copies attach to the cell membrane 2. plasmids also replicate 3. cell membrane begins to grown between the two DNA molecules and begins to pinch inward, dividing cytoplasm into two 4. a new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids

Question 57

how do viruses replicate

Answer 57

- by attaching to their host cell with the attachment proteins on their surface - They then inject their nucleic acid into the host cell - The genetic information on the injected viral nucleic acid then provides the ‘instructions’ for the host cell’s metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins, which are then assembled into new viruses