Cell Structure (complete)

Question 1

Suggest why eukaryotic cells evolved from prokaryotic cells.

Answer 1

• adaptation of circular DNA into enclosed DNA in a nucleus.
• adaptation of organelles without membranes to organelles with membranes.
• the inability of the cell to create it’s own mitochondria/chloroplasts.
• the mitochondria/chloroplasts having their own DNA and ribosomes.

Question 2

Give the overall function of:
- the nucleus
- the mitochondria

Answer 2

Nucleus;
- control centre of the cell through the production of mRNA and tRNA, hence protein synthesis.
- retains cells genetic material in form of DNA and chromosomes.
- manufactures ribosomal RNA and ribosomes.

Mitochondria;
- site of aerobic respiration, therefore responsible for production of ATP from respiratory substances.

Question 3

Give the overall function of:
- the golgi apparatus
- the chloroplasts

Answer 3

Golgi Apparatus;
- modify proteins using carbohydrates to form glycoproteins.
- produce secretory enzymes, and lysosomes.
- secrete carbohydrates.
- transport, modify and store lipids.

Chloroplasts;
- site of photosynthesis.
- manufactured some proteins required for photosynthesis.

Question 4

Give the overall function of:
- lysosomes
- ribosomes

Answer 4

Lysosomes;
- hydrolyse pathogens ingested by phagocytes
- release enzymes outside cells to destroy surrounding materials.
- digest worn out organelles so useful chemicals can be re-used.
- completely break down dead cells.

Ribosomes;
- site of protein synthesis in cells (translation).

Question 5

Give the overall function of:
- smooth endoplasmic reticulum
- rough endoplasmic reticulum

Answer 5

Smooth Endoplasmic Reticulum;
- synthesises, stores and transports lipids and carbohydrates.

Rough Endoplasmic Reticulum;
- provides large surface area for protein and glycoproteins synthesis.
- provides pathway for the transport of material throughout the cell.

Question 6

Explain the different types of electron microscope.

Answer 6

Transmission electron microscope;
- an electron gun shoots a beam of electrons that penetrates the specimen from below, being focused on the specimen by a condenser electromagnet.
- the parts of the specimen that absorb electrons appear dark, others appear light.

Scanning electron microscope;
- a beam of electrons directed onto specimen from above, being passed back and forth in a regular pattern.
-the pattern of the scattering depends on the contours of the specimens surface.

Question 7

Give the limitations of the two types of electron microscope.

Answer 7

TEM -
- whole system must be in vacuum, so no living specimen.
- specimen must be extremely thin, so electrons can pass through.
- complex staining process required, however only black and white image produced.
- image may contain artefacts from preparation.

SEM -
- whole system must be in vacuum, so no living specimen.
- lower resolving power than TEM.
- complex staining process required, however only black and white image produced.
- image may contain artefacts from preparation.

Question 8

What is Cell Fractionation?
Describe the two stages in Cell Fractionation.

Answer 8

• The process where cells are broken up and the different organelles they contain separated.

1 - Homogenation;
- cells are mixed with a cold, isotonic, buffer solution and broken up in a homogeniser, releasing the organelles from the cells, then filtered to remove any whole cells or debris.
2 - Ultracentrifugation;
- filtrate placed in a centrifuge and spun at slow speed. heaviest organelles separated to bottom. supernatant removed. process repeats at higher and higher speeds until all organelles separated.

Question 9

Describe what happens at each of the 5 (1+ 4) stages of mitosis.

Answer 9

Interphase;
- DNA/genetic info replicates.

Prophase;
- chromosomes condense and become visible, the nucleolus disappears and the nuclear envelops disintegrates.
- spindle fibres begin forming.
Metaphase;
- chromosomes line up on equator of cell. spindle fibres begin attaching to chromatids.
Anaphase;
- the spindle fibres attached to chromatids retract to respective poles of the cell, taking chromatids with them.
Telophase;
- spindle fibres disintegrate as chromosomes reach poles and become indistinct.
- nuclear envelope and nucleolus reforms.

Question 10

What is the importance for mitosis in:
- Growth
- Repair
- Reproduction

Answer 10

Growth;
- when two haploid cells fuse together into a diploid cell they contain all the genetic information required to form the new organism. if the new organism is to resemble it’s parents, all the cells grown from the original cell must be genetically identical.
Repair;
- if cells are damaged or die, it is important that the new cells formed have identical structure and function to the ones that have been lost.
Reproduction;
- single celled organisms divide by mitosis to give two new organisms. each new organism is genetically identical to the parent organism.

Question 11

Describe the 4 stages of binary fission.

Answer 11

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

Question 12

Describe the 4 stages of Viral replication.

Answer 12

1 - The virus attaches onto a host cell (T Helper cell) using attachment proteins.
2 - The virus injects nucleic acid contains genetic information into the host cell. (reverse transcriptase and RNA)
3 - The genetic information provides instructions for the host cells metabolic processes to produce viral components.
4 - the viral components are produced and formed into new viruses, which leave the host cell.

Question 13

What are the two types of cancer?
(Name and describe briefly)

Answer 13

Benign - slow growing tumours, that are more compact and less likely to be life threatening.
Malignant - rapidly growing tumours, that are less compact and more likely to be life-threatening as they can produce tumours in other cells, and travel in the bloodstream.

Question 14

What is a common treatment for cancer?

Answer 14

Chemotherapy;
- disrupts the cell cycle, however affects all dividing cells.
- prevents DNA replication.
- Interferes with spindle formation in metaphase.

Question 15

What are the steps in a drug trial?

Answer 15

Pre-clinical;
- Test on isolated molecule
- Test on cell/tissue culture
- Test on small mammal (mouse)

Clinical;
- Test on healthy volunteers (for side effects)
- Test on patients (for optimum doseage)
- Test on large group (>1000) (double-blind trial)

Question 16

How do you calculate mitotic index?

Answer 16

((Number of cells undergoing mitosis) / (total number of cells)) x100

Question 17

Name and describe (if needed) the main points of structure of the nucleus.

Answer 17

• Nucleolus - manufactures ribosomal RNA and assembles the ribosomes. (may be >1 in nucleus)
• Chromatin - ‘stringed’ chromosomes (DNA)
• Nucleoplasm - granular, jelly-like material that makes up the bulk of the nucleus.
• Nuclear envelope - double membrane that surrounds the nucleus, controls entry and exit of materials in and out of the nucleus and contains nuclear reactions within.
• Nuclear pores - control entry/exit of large molecules in and out of the nucleus.

Question 18

Name and describe (if needed) the main points of structure of mitochondria.

Answer 18

• Matrix - contains DNA, lipids, proteins and ribosomes to allow control over production of some of its own proteins, contains many respiration involved enzymes.
• Cristae- provides large surface area for attachment of enzymes and other proteins involved in respiration.
• Double membrane - controls entry/exit of materials in the mitochondria.

Question 19

Name and describe (if needed) the main points of structure of the golgi apparatus.

Answer 19

• Stacks of membranes (cisternae)
• Vesicles (secretory/transport) - Secretory vesicles may move to cell surface after being pinched off from ends of cisternae, to then fuse with the cell membrane and release contents outside of the cell. Transport vesicles transport modified proteins and lipids.

Question 20

Name and describe (if needed) the main points of structure of the chloroplast.

Answer 20

• Stroma - fluid-filled matrix where 2nd stage of photosynthesis occurs. Contains all enzymes needed to make sugars in 2nd stage of photosynthesis, and contains the chromosomal DNA.
• Chloroplast envelope - double plasma membrane that surrounds organelles, highly selective control over entry/exit of materials in and out the chloroplast.
• Grana - stacks of <100 thylakoids, where 1st stage of photosynthesis occurs.
• Granal membranes - provides large surface area for attachment of chlorophyll, electron carriers and enzymes to carry out 1st stage of photosynthesis.
• Thylakoids - some have tubular extensions which join to thylakoids in adjacent grana, contain chlorophyll.

Question 21

Name and describe (if needed) the main points of structure of the lysosomes.

Answer 21

• Membrane
• Enzymes (inside lysosomes)
• Transport proteins (found on outer membrane)

Question 22

Name and describe (if needed) the main points of structure of the endoplasmic reticulum.

Answer 22

• Ribosomes - found on outside of cisterna in rough endoplasmic reticulum.
• Cisternal space (lumen)
• Cisternae - where the ribosomes are found.

Question 23

Name and describe (if needed) the main points of structure of the ribosomes.

Answer 23

• Large and small sub-unit - contains ribosomal RNA and proteins

Question 24

Why is a cold, isotonic, buffer solution used during the blending up of cells before cell fractionation?

Answer 24

• The cells are mixed into the solution before being blended.
  It is:
  > Isotonic - to prevent osmosis into the cells to prevent them from bursting.
  > Cold - to reduce enzyme activity that may affect the organelles.
  > Buffer - so pH doesn’t fluctuate and affect the results.