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Biology > M2 Cell Structure and Replication > Flashcards

M2 Cell Structure and Replication Flashcards

Virus, Bacteria and Cell Structure and Replication.

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1
Q

What are the differences between a light and electron microscope?

A

Electron:
- Up to around x100,000
- High resolution
- Expensive
- Large
- Requires training to use
- Black and white images
- Specimen dead
etc

Light:

  • Up to around x1000
  • Lower resolution
  • Cheap
  • Small and portable
  • Easy to use
  • Colour maintained
  • Specimen living or dead
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2
Q

What is the equation for magnification?

A

Magnification = Image size / Actual Size (IAM triangle)

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3
Q

How do you convert from mm to micrometres to nm?

A

x1000

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4
Q

Why do light microscopes have a lower resolution than electron microscopes?

A

The wavelength of light is too long.

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5
Q

What are the differences between prokaryotic and eukaryotic cells? (8 structural, 1 functional)

A

Prokaryotic vs Eukaryotic

  • No nucleus but circular DNA vs DNA found in a nucleus
  • DNA not associated with proteins vs DNA is associated with histone proteins
  • Some DNA found in plasmids vs no plasmids
  • No membrane-bound organelles vs contains membrane-bound organelles (e.g. mitochondria)
  • No chloroplasts but chlorophyll associated with the cell surface membrane in some vs plant cells contain chloroplasts
  • Smaller Ribosomes (70s) vs Larger Ribosomes (80s) - also contain 70s in mitochondria and chloroplasts
  • Cell walls made of murein vs cell walls made of cellulose in plant cells
  • May have outer mucilaginous layer (slime capsule) vs no slime capsule

Function:
Binary fission vs mitosis and meiosis

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6
Q

Describe the steps in cell fractionation

A

1) Chop up tissue in ice-cold, isotonic buffered solution.
2) Put the chopped tissue into a blender
3) Filter the mixture
4) Pour the mixture into tubes and spin in a centrifuge
5) The supernatant (liquid layer) is poured into a fresh tube
6) Supernatant spun at a faster speed (medium)
7) Supernatant from second tube spun at a faster speed (high)

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7
Q

In cell fractionation, what will you find in the sediment of tube 1, 2 and 3?

A

1) Nuclei
2) Mitochondria
3) Ribosomes, membranes etc

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8
Q

In step 1 of cell fractionation, why is ice-cold, isotonic, buffered solution used?

A

Ice-cold:
Minimises enzyme activity to prevent damage to organelles.

Isotonic:
Same water potential as inside the organelles so they don’t shrivel/swell and burst due to osmosis.

Buffered:
Maintains pH so proteins are not denatured.

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9
Q

Why do you blend the tissue and filter it in cell fractionation?

A

To break open cells and remove debris (large pieces)

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10
Q

Why is cell fractionation performed?

A

So you can examine the organelles in a cell separately.

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11
Q

Describe the nucleus. What is it’s function?

A

Spherical, consisting of a nuclear envelope with nuclear pores surrounding the nucleoplasm containing genetic material (chromatins or chromosomes) and the nucleolus.

Controls protein synthesis. Retains genetic information. Manufactures rRNA and assembles ribosomes.

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12
Q

Describe Mitochondria. What is it’s function?

A

Rod shaped - consisting of an outer and inner membrane. The inner membrane is highly folded to form cristae. In between membranes is the inter-membrane space. The fluid inside the mitochondria is called the matrix, which also contains a small amount of loose (circular) DNA and small ribosomes (70S).

ATP production.

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13
Q

Describe Chloroplasts. What are their function?

A

Consists of an inner and outer membrane and a fluid filled centre called the stroma. Inside the stroma are parallel flattened sacs of membranes called thylakoids, stacked in places to form grana. Thylakoids contain chlorophyll. In between the grana the membranes are called lamella. Chloroplasts also contain a small amount of loose DNA, small ribosomes and starch grains.

Harvest sunlight and carry out photosynthesis.

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14
Q

Describe the Rough Endoplasmic Reticulum. What is it’s function?

A

An extensive membrane system of flattened sacs (cisternae) which is continuous with the nuclear membrane and may link with the Golgi apparatus. These membranes are covered in ribosomes.

Provides a large surface area for protein synthesis (and synthesis of glycoproteins) and act as a transport system for the products of protein synthesis.

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15
Q

Describe the Smooth Endoplasmic Reticulum. What is it’s function?

A

An extensive membrane system of flattened sacs (cisternae) - not covered in ribosomes, but has a smooth appearance.

Synthesises, stores and transports lipids and carbohydrates.

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16
Q

What is the Golgi apparatus? What is it’s function?

A

A stack of membranes that make up cisternae, similar to SER but more compact and with vesicles.

Has many functions linked to modification and packaging of products of the RER and SER:

e. g.
- Forming glycoproteins (carbohydrates plus proteins)
- Producing secretory enzymes
- Secreting carbohydrates
- Transport, modify and store lipids
- Form lysosomes

17
Q

What are lysosomes? What are their function?

A

Formed from vesicles produced by Golgi apparatus, containing hydrolytic enzymes.

Functions include:

  • Hydrolysing material ingested by phagocytosis
  • Exocytosis to release enzymes outside of cell.
  • Digest worn-out organelles to recycle their contents
  • Breaking down dead cells.
18
Q

What are ribosomes? What are their function?

A

Smallest of cell organelles.
There are 2 types: 80S (larger - found in eukaryotic cells) and 70S (smaller - found in prokaryotic cells, mitochondria and chloroplasts).
They consist of 2 subunits (one smaller, one larger) made from rRNA and proteins.

They are the site of protein synthesis.

19
Q

What is the cell wall? What is it’s function?

A

Found only in plant cells, outside of the cell surface membrane, made mainly of cellulose.

Supports the structure of the cell, withstanding osmotic pressure from within the cell, enabling the cell to remain turgid.

20
Q

What is the large central vacuole? What is it’s function?

A

Only found in plant cells, a large organelle surrounded by a single membrane called the tonoplast. Fluid inside is often referred to as cell sap (containing salts, sugars, amino acids, wastes and pigments).

Used as a storage site, supporting plants by making cell turgid. May also contain pigments which colour petals to attract pollinators.

21
Q

What are the stages of Mitosis called?

A

Prophase, Metaphase, Anaphase, Telophase (and cytokinesis)

PMAT

22
Q

What is the part of the cell cycle where mitosis isn’t taking place called? What are it’s stages?

A

Interphase:

  • G1 (growth)
  • S (DNA replication)
  • G2 (preparation for mitosis - e.g. synthesis of proteins and ATP)

note: chromosomes are not visible during this phase

23
Q

Describe the structure of chromosomes

A
  • composed of DNA and Histone proteins
  • appear as paired chromatids joined at the centromere
24
Q

What is mitosis for?

A

Growth, asexual reproduction and replacing worn out cells

25
Q

What happens in cytokinesis?

A

Occurs by the cleavage of the cell membrane, the cytoplasm then divides forming 2 daughter cells.

Plant cells: cell plate forms across the equator and a new cell wall is laid.

26
Q

What happens in Prophase?

A
  • Chromosomes become shorter and thicker
  • Centrioles divide and move to poles of the cells
  • Spindle fibres form from each centriole, forming across the cell.
  • Nuclear membrane disintegrates and nucleolus disappears.
27
Q

What happens in Metaphase?

A
  • Chromosomes arrange themselves at the equator.
  • They attach to the spindle fibres at the centromere.
28
Q

What happens in Anaphase?

A
  • A very rapid stage
  • Centromere divides, spindle fibres contract and shorten, and pull the separated chromatids to opposite poles.
  • Energy provided by mitochondria around spindle fibres.
29
Q

What happens in Telophase?

A
  • Chromosomes have reached the poles, they uncoil and lengthen to become chromatin.
  • Nucleoli reappear and nuclear membrane reforms
30
Q

What is the equation for mitotic Index?

A

Number of cells in mitosis / total number of cells

(decimal number)

31
Q

Name the structures of prokaryotic cells.

A
  • Murein cell wall
  • Slime Capsule
  • Cell-surface membrane
  • Circular DNA
  • Plasmid
  • Flagella
32
Q

What is the role of the murein cell wall in prokaryotic cells?

A

Protects against physical damage and cell lysis (cell membrane broken down). Prevents entry of certain substances.

33
Q

What is the role of the slime capsule in prokaryotic cells?

A

Protects bacteria from other cells and helps them stick together for further protection.

34
Q

Describe the process of binary fission.

A

1) The circular DNA is copied once.
2) The two DNA loops attach to the membrane.
3) The membrane elongates between the DNA molecules and pinches inwards forming two separate cells.
4) A new cell wall forms, dividing the cell into two identical daughter cells.

35
Q

How do viruses replicate?

A

By attaching to receptors on a host cell with their attachment proteins. They inject their genetic material into the host cell - providing instructions to produce viral components. These then assemble into new viruses and usually burst out of the cell to infect other cells.

36
Q

Name the structures found in Viruses.

A
  • DNA or RNA
  • Enzymes (e.g. Reverse Transcriptase)
  • Capsid (protein coat)
  • Matrix
  • Lipid envelope (sometimes)
  • Attachment proteins (attached to either lipid envelope or capsid)
37
Q

What are the differences between a scanning electron microscope and a transmission electron microscope?

A

SEM: 3D, x100,000 magnification, electrons bounce off surface of sample, lower resolution

TEM: 2D, x500,000 magnification, electrons pass through sample, higher resolution

Biology (17 decks)

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