Foundations in Biology Module 2 > Cell Structure > Flashcards

Cell Structure Flashcards

Topic 1.1 (101 cards)

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1
Q

What is the structure of the nucleus?

A

The nucleus contains genetic information in the form of chromosomes (chromatin - DNA & histone protein).

The nucleus contains a structure called the nucleolus.

The nucleus has a double membrane known as the nuclear envelope, which contains nuclear pores to allow substances to enter or leave the nucleus.

Largest cell organelle (3-10microm)

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2
Q

What is the function of the nucleus?

A

The nucleus controls the activities of the cell - the nucleus contains DNA, which contains the instructions for making proteins. Specific genes from the DNA are copied into mRNA (transcription) and then the ribosomes use that mRNA to make proteins (translation).

The nucleolus is responsible for making ribosomal RNA (rRNA).

The nuclear pores within the nuclear envelope allow the nucleus to exchange substances between the cytoplasm and the nucleus, for example mRNA leaves to enter a ribosome, and proteins enter because of transcription.

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3
Q

What is the structure of the nucleolus?

A

The nucleolus is not surrounded by a membrane.

The nucleolus is made of DNA, RNA and proteins all clustered together.

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4
Q

What is the function of the nucleolus?

A

The nucleolus is the site of ribosome synthesis. The nucleolus creates rRNA. In the cytoplasm, ribosomal proteins are synthesised. The ribosomal proteins enter the nucleus via the nuclear pores, and then enter the nucleolus, where the proteins and rRNA combine. This makes both the large and small subunit of the ribosome. The subunits leave through the nuclear pores, and combine to make a fully functional ribosome. The ribosome remains in the cytoplasm floating freely, or attached to the rough endoplasmic reticulum.

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5
Q

What is the structure of the mitochondria?

A

Spherical / oval shaped.

The mitochondria has a double membrane. The outer membrane is smooth and acts as a barrier, where the inner membrane folds into structures called cristae.

Cristae has a large surface area so that the enzymes involved in aerobic respiration work faster.

There is an enzyme rich layer known as the matrix.

The matrix contains enzymes, mtDNA and ribosomes. This means that mitochondria is able to make its own enzymes and proteins.

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6
Q

What is the function of mitochondria?

A

The mitochondria is the site of aerobic respiration - it produces ATP.

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7
Q

What is the structure of the lysosomes?

A

Lysosomes are surrounded by a membrane to keep the enzymes separate from the cytoplasm of the cell to prevent self digestion.

They contain hydrolytic enzymes. Hydrolytic enzymes break substances down by adding water. They break down lipids, proteins, carbohydrates and nucleic acids, as well as waste and pathogens.

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8
Q

What is the function of the lysosomes?

A

Digest pathogens using the hydrolytic enzymes.

Digest waste material using the hydrolytic enzymes - they digest old or damaged organelles (autophagy) and dead cells, recycling them for the cell to use.

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9
Q

What is autophagy?

A

The process by which a cell digests it’s own damaged or worn out organelles using lysosomes.

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10
Q

What is the cytoskeleton?

A

The cytoskeleton is present throughout the cytoplasm and provides support, structure and strength to the cell.

Helps with movement, transport within the cell and mechanical strength.

It contains 3 components: microfilament, microtubule, intermediate filaments.

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11
Q

What is the structure and function of microfilaments?

A

Made of protein actin.

Cytokinesis

Microfilaments are involved in the cells movement and locomotion (cells’ ability to move) such as crawling and muscle contraction.

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12
Q

What is the structure and function of microtubules?

A

Made of the protein tubulin.

Forms a scaffold-like structure throughout the cell.

Forms the mitotic spindle during cell division.

Acts as tracks for intracellular transport (vesicles, organelles, proteins).

Maintains the shape of the cell.

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13
Q

What is intracellular transport?

A

The movement of organelles or molecules inside the cell.

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14
Q

What is the structure and function of the intermediate filaments?

A

Made of various proteins, depending on the cell type.

Holds organelles in place.

Provides mechanical strength to tissues, like skin or hair.

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15
Q

What are vesicles?

A

Vesicles are tiny sacs that are made of a lipid bilayer membrane. They transport substances around the cell, and sometimes store them temporarily. They travel along the tracks of the microtubule.

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16
Q

What is the structure of the rough endoplasmic reticulum?

A

Contains a network of membranes enclosing a fluid-filled space known as cisternae. Within the cisternae, proteins can be temporarily stored or transported via the microtubules.

Covered with ribosomes, hence why it is called the rough endoplasmic reticulum.

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17
Q

What is the function of the rough endoplasmic reticulum?

A

Synthesis and transport of proteins, made using the many ribosomes. They are transported by moving through the cisternae, and packaged into vesicles.

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18
Q

What is the structure of the smooth endoplasmic reticulum?

A

Contains a network of membranes enclosing a fluid-filled space known as cisternae.

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19
Q

What is the function of the smooth endoplasmic reticulum?

A

Synthesis of lipids, including phospholipids and cholesterol.

Synthesis of carbohydrates

Produce steroid hormones form the cholesterol.

Transporting lipids and carbohydrates by packaging them in vesicles.

Storing lipids and carbohydrates.

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20
Q

What is the structure of ribosomes?

A

Consists of a large and a small subunit.

No membrane surrounding it.

Measured in S - there ate 80S in eukaryotic cells, and 70S in prokaryotic cells.

Made up of ribosomal proteins and rRNA.

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21
Q

What is the function of ribosomes?

A

Protein synthesis (translation).

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22
Q

What is the structure of the Golgi apparatus?

A

Contains cisternae.

Surrounded by vesicles, which carry molecules to and from Golgi.

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23
Q

What is the function of the Golgi apparatus?

A

Process, package and transport the lipids and proteins received from the SER/RER.

Some specialised vesicles become lysosomes (lysosome synthesis).

They can process the lipids and proteins by modifying them, for example adding sugar to a protein.

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24
Q

What is magnification?

A

How many times larger the image is than the object.

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25
What is resolution?
The ability to distinguish between two separate points (or a measure of how detailed an image is).
26
What is the equation for image size?
I = AM
27
What is an eyepiece graticule and what is it used for?
An eyepiece graticule is placed inside the eyepiece lens, and it is a small scale with divisions ranging from 0-100. For each objective lens, it is used to determine a calibrated value to use for measuring the actual length of structures.
28
What is a stage micrometer ?
A micrometer ruler is used alongside an eyepiece graticule to work out the calibrated value for each objective lens. It is attached to the stage. Each division is often 10 micro metres.
29
How is a calibrated value determined?
Count how many divisions of the eyepiece graticule fit into one division of the stage micrometre. Divide the length of one division of the stage micrometre (often 10 micrometres) by the number of divisions of the eyepiece graticule. Repeat this for the different objective lenses to use to measure the actual length of the structures.
30
What is the resolution and maximum magnification of a light microscope?
Resolution - 0.2 micrometres (200nm) Maximum magnification - x1500
31
How do you prepare a slide using the wet mount method?
1. Use a pipette and add a droplet of water into the middle of the slide. 2. Use forceps to place a very thin piece of the specimen into the water droplet. It needs to be thin to allow the light to pass through the specimen. 3. Add a stain (such as iodine from potassium iodide) using a clean pipette to add contrast and highlight the structures. 4. Place a cover slip on top, being careful to avoid any bubbles.
32
What is differential staining?
Using more than one chemical stain that can also be used to distinguish between cells or organelles. Different organelles are stained with one dye whereas another organelle is stained with another to make finding the organelle easier. Can also be used to distinguish between two types of microorganisms.
33
What is a dry mount?
The specimen is placed directly onto the slide and covered with a cover slip. No stain.
34
What is a squash slide?
A wet mount is prepared (either water or oil) and the cover slip is pressed to squash the cells.
35
What is a smear slide?
The edge of a slide is used to smear the sample to create a thin, even coating on a separate slide. Wet mount. Often used for blood samples.
35
How do you use a light microscope?
Clip the prepared microscope slide onto the stage. Select the objective lens with the lowest power. Use the coarse focus to bring the stage just below the objective lens. Look down the eyepiece and use the coarse focus to move the stage downwards until the image is roughly in focus. Use the fine focus to make the image clearer. If a higher magnification is needed, swap to a more powerful objective lens and refocus.
36
What should biological drawings contain?
A clear title of what type of cell it is. Clean lines done with a sharp pencil. Continuous lines. The magnification. The scale used. Labels of the sub-cellular structures.
37
What are artefacts?
Artefacts are things such as dust, fingerprints and air bubbles that can be seen within the image as a result of complex preparation of the specimen, such as dehydrating it or coating it in wax and embedding it in resin. The actual specimen does not have those artefacts, but it is seen only on the image.
38
What do transmitting electron microscope do to view a specimen? (TEMs) How do they work?
They use electromagnets to transmit a beam of electrons through the specimen, which must be thin to allow the electrons to pass through. The denser parts of the specimen absorb more of the electrons, and so the image will appear darker.
39
What do TEMs need to work?
The electrons must be transmitted through a vacuum, so the specimen must be dead.
40
Are TEMs able to view the internal structure of organelles? Why?
Yes. Electrons have a large wavelength, so the resolution of a TEM is 0.5nm, and the magnification is able to go up to x500,000.
40
Why can electron microscopes only work in a vacuum?
Vacuums have no particles. Air particles would scatter the electrons, so because vacuums have no particles the electrons are able to form a clear image.
41
What do scanning electron microscope do to view a specimen? (SEMs) How do they work?
SEMs scan a beam of electrons through the specimen. The reflected electrons are then used to form the 3D image. The specimen can be thicker for the SEM than the TEM. Also done in a vacuum.
42
What is the maximum magnification and the resolution of SEMs?
Magnification - 100,000 Resolution - 3-10nm
43
How do laser scanning confocal microscopes work?
They use a laser beam to scan thin sections of a live specimen and build a high-resolution 3D or 2D image, often with fluorescent stains to highlight structures. A dichroic mirror is used.
44
How do laser scanning confocal microscopes compare with electron microscopes?
LSCM have a lower resolution than electron microscopes. The specimen used can be living.
45
What are eukaryotic cells?
Cells that contain a nucleus and membrane-bound organelles.
46
What are eukaryotes?
They are often multicellular organisms that are made up of eukaryotic cells (animal, plant, fungi)
47
What does multicellular mean?
Multiple cells working together.
48
What are prokaryotes?
These are single-celled organisms made up of prokaryotic cells like bacteria.
49
What is the structure of a cell wall?
Made of cellulose. Contains channels (gaps) called plasmodesmata.
50
What is the function of a cell wall?
Supports the cell - when the vacuole fills with water, it swells. This swelling causes the cytoplasm to move outwards against the cell membrane. The cell membrane therefore pushes against the cell wall. This is called turgor pressure, which keeps the cell firm and rigid. Prevents the cell from bursting - the cell wall can withstand high osmatic pressure. Substances can be exchanged between the plant cells through the plasmodesmata connecting neighbouring cells.
51
Where are chloroplasts found?
Green parts of the plant, like the stem and leaf.
52
What is the structure of chloroplasts?
They contain fluid filled sacs known as thylakoids which stacked up to form grana. They are surrounded by a double membrane which encloses a fluid called stroma. They contain their own DNA and ribosomes.
53
What is the function of a chloroplast?
Site of photosynthesis. The reactions take place in the grana and stroma.
54
What is the structure of the vacuole?
Fluid filled sac that contains cell sap (a weak solution of sugars, salts and dissolved substances). Surrounded by a selectively permeable membrane known as tonoplast, which controls the movement of substances into and out of the vacuole.
54
Describe the structure of algal cells?
Can be either multicellular or unicellular. Contains all of the same organelles found within a a plant cell. Chloroplasts are shaped differently than what they would be within a plant cell.
55
Describe the structure of fungal cells?
Can be either multicellular or unicellular. Contains all of the organelles found within a plant cell except for chloroplasts. Cell wall is made of chitin rather than cellulose.
56
What are prokaryotes?
Prokaryotes are unicellular organisms that are made up of prokaryotic cells. The prokaryotic cells do not have membrane bound organelles, or a nucleus. They are much smaller than eukaryotic cells.
57
Compare eukaryotic cells and prokaryotic cells?
Eukaryotic cells have a cell wall made of cellulose, whereas the cell wall in prokaryotic cells is made of murein. Eukaryotic cells contain a nucleus, whereas prokaryotic cells do not, and instead store most of their genetic material within a circular strand of DNA (nucleoid), with some extra genes in stored in extra loops called plasmids. Ribosomes in prokaryotic cells are much smaller, at S70, where eukaryotic cells are S80.
58
Describe the capsule?
Some prokaryotic cells contain an extra layer called a capsule around its cell wall. The capsule is made of polysaccharides and protects the cell from attack from antibiotics or white blood cells.
59
Describe the flagellum? (short)
Some prokaryotes contain a long, hair-like structure known as a flagellum. This structure is attached to the cell membrane and rotates to push the cell through its environment.
60
Describe pili?
Some prokaryotes contain short, hair-like structures on the cell surface known as pili. Pili are used for attaching prokaryotic cells to other cells or surfaces.
61
How do you work out the total magnification?
Multiply the eyepiece lens magnification (often x10) by the magnification of the selected objective lens.
62
Why should materials that have the same refractive index as glass be used as a wet mount?
It prevents diffraction between liquid and gas, as well as reducing the amount of distortion of the image.
63
What does the fine focus knob do?
Alters the resolution.
64
What happened in 1665 regarding cell theory? (RH)
Robert Hooke observed ‘cells’ in cork.
65
What happened in 1674 - 1683 regarding cell theory? (AvL)
Anton van Leeuwenhoek observes living cells for the first time using powerful objective lenses.
66
What happened in 1832 regarding cell theory? (Dur)
Durmotier observed cell division in plants.
67
What happened in 1833 regarding cell theory? (Bro)
Brown describes the cell nucleus.
68
What happened in 1837 - 1838 regarding cell theory? (SSP)
Cell theory becomes widely accepted after findings from Schleiden, Purkynê and Schwaan.
69
What happened in 1844 regarding cell theory? (Rem)
Cell division in animals is observed by Remak.
70
What happened in 1860 regarding cell theory? (Pa)
Pasteur highlights the importance of external resources for cells.
71
What does the iodine stain do?
Can enter the cell wall of plants, as well as in the nuclear pores of the nuclear envelope, which makes structures more visible under a microscope.
72
What does the methylene blue stain do?
It is a positively charged dye which is attracted to the negative molecules of the cell.
73
What are the two types of differential staining?
Gram Acid fast
74
What does Gram staining do?
Separates bacteria into two groups, Gram positive and Gram negative based on their cell wall.
75
What does Gram positive bacteria look like?
Has a thick peptidoglycan layer with an outer lipid membrane.
76
What does Gram negative bacteria look like?
Has a thinner peptidoglycan layer with no outer lipid membrane.
77
How is Gram bacteria detected?
Place the Gram bacteria onto a Petri dish. Apply crystal violet for 30 seconds. Apply iodine to fix the crystal violet. Use ethanol (alcohol) to decolourise. - If it is Gram positive, the bacteria will retain the crystal violet and will appear blue, violet. - If it is Gram negative, the bacteria will lose the crystal violet and then a counterstain is used called safranin, which will make the bacteria appear pink or red.
78
What is Fast Acid used for?
Used for identifying species of Mycobacterium, such as M. tuberculosis (which causes tuberculosis) and M. leprae (which causes leprosy).
79
Why is Fast Acid used for Mycobacterium instead of Gram?
The Mycobacterium are resistant to Gram staining.
80
What stains are used for Fast Acid?
Carbol Fuchsin (red/purple) Alcohol Methylene blue
81
Why is the resolution for light microscopes 200nm (0.2microm)?
The wavelength of visible light is 400nm, so the resolution is half of the wavelength.
82
What happens to objects at a high resolution?
Two objects that are close together are seen as separate entities.
83
How to prepare the stain used in electron microscopy?
Heavy positively charged metal ions are used to stain the specimens (omnium, lead or uranium). This is to make organelles distinct and for organelles and membranes to absorb negatively charged electrons differentially. Electrons are unable to pass through stained areas, which produces electron shadows that improve contrast.
84
How can the specimen be complexly prepared for electron microscopy?
Fix the specimen using a fixative (omnium tetroxide). Dehydrate it using ethanol. Embed it in resin.
85
Describe features of TEMs?
Forms 2D images that have a higher resolution than SEMs. Only the electrons passing through the structures can be seen. Can see the internal structure of the cell. Dead specimen. Vacuum. Black and white image.
86
Describe the features of SEMs?
Forms 3D, lower resolution images than TEMs. The images are 3D because of the greater depth of field. Cannot observe internal structure of cells. Dead specimen. Vacuum. Black and white image.
87
Why do electron microscopes have a higher resolution than light microscopes?
The short wavelength of the radiation (the electron beam) used to form the images. Light has a longer wavelength.
88
What are the advantages of electron microscopes?
Higher resolution and magnification. Ultrastructure with the TEM. SEM gives depth of field.
89
What are the disadvantages of electron microscopes?
Dead specimens are used. Specimen needs to be dehydrated which can cause artefacts. Vacuum pump required. High voltage so high cost and safety risk.
90
What is a fluorescent dye?
When a chemical absorbs and then emits light but at a longer wavelength and a lower energy.
91
What can laser scanning confocal microscopy be used for?
Because they aren't invasive, they can be used for endoscopy and detecting eye diseases / defects, especially because a thick specimen / tissue is used and scanned with the laser beam
92
What are the advantages of LSCM?
They can use use thick or 3D specimens. They allow external 3D structure of the specimen to be observed. Very clear images. High resolution.
93
What are the disadvantages of LSCM?
Slow process. Laser can cause photodamage to cells..
94
What is the structure and function of centrioles?
Centrioles are organelles that help organise spindle fibres — they don’t make up the fibres themselves. Centrioles are a component of the cytoplasm present in most eukaryotic cells with the exception of flowering plants and most fungi. They are composed of microtubules. Two associated centrioles form the centrosome, which is involved in the assembly and organisation of the spindle fibres during cell division. (The spindle fibres form the mitotic spindle).
95
What is flagella? (long)
Whip-like extensions that protrude from some cell types. They are longer than cilia, but cilia are found in greater numbers. Flagella are primarily used to enable a cell's motility. In some cells, they are used as a sensory organelle detecting chemical changes in a cell's environment.
96
What is the structure and function of cilia?
Cilia can be mobile or stationary. Stationary cilia are present on the surface of many cells and have an important function in sensory organs such as the nose. 9 + 0 arrangement (no two central microtubules). Mobile cilia beat in a rhythmic manner, creating a current, and causes fluids or objects adjacent to the cell to move. Each mobile cilium contains two central microtubules (black circles) surrounded by nine pairs of microtubules arranged like a wheel - this is known as the 9 + 2 arrangement. Pairs of parallel microtubules slide over each other causing the cilia to move in a beating motion.
97
Describe the 5 stages of protein production?
Proteins are synthesised on the ribosomes bound on the RER. They then pass into the RER's cisternae and are packaged into transport vesicles. Vesicles containing the newly synthesised proteins move towards the Golgi apparatus via the transport function of the cytoskeleton. The vesicles fuse with the cis face of the Golgi and the proteins enter. The proteins are structurally modified before leaving the Golgi in vesicles from its trans face. Secretory vesicles carry proteins that are to be released from the cell. The vesicles move towards and fuse with the cell surface membrane, releasing their contents by exocytosis. Some vesicles form lysosomes.
98
What is staining used for?
Identify organelles Increase contrast Make it easier to see organelles
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