Topic 3 Cell biology

Question 1

Compare and contrast the structure of the two categories of cell: eukaryotic and prokaryotic cell

Answer 1

eukaryotic has membrane bound organelles, prokaryotic does not.
Eukaryotic has cellulose cell walls, prokaryotic has peptidoglycan cell walls.
Eukaryotic has Linear DNA, Prokaryotic has circular DNA.
Both have cytoplasm
Both are surrounded by a cell membrane.

Question 2

Describe the structure and function of a nucleus

Answer 2

made of nucleolus, nuclear membrane with nuclear pores and chromosomes, contains dna which is used to produce mRNA for protein synthesis

Question 3

Describe the structure and function of a nucleolus

Answer 3

produces ribosomes

Question 4

Describe the structure and function of a ribosome

Answer 4

used for protein synthesis for reading mRNA codons. Found on the rough endoplasmic reticulum

Question 5

State the function of the flagellum in sperm cells

Answer 5

Movement of the cell through a fluid

Question 6

State the function of the mitochondria in a sperm cell

Answer 6

Production of ATP energy via aerobic respiration

Question 7

State the function of the acrosome in sperm cells

Answer 7

releases enzymes used to break down the zona pellucida around the egg cell to allow the sperm cell to reach the cell membrane.

Question 8

State the function of the haploid nucleus in sperm cells

Answer 8

Contains half of the dna required to form a diploid nucleus inside an egg cell.

Question 9

State the function of lipid droplets in ovum cells

Answer 9

Provides fuel for respiration to provide energy for cell replication after fertilisation

Question 10

State the function of the cortical granules inside an egg cell

Answer 10

Move into the zona pellucida which causes the zona pellucida to thicken and harden to prevent polyspermy as acrosome reaction cannot occur.

Question 11

State the function of the zona pellucida in ovum cells

Answer 11

releases chemicals to attract sperm cells via chemotaxis, acts as a physical barrier after cortical reaction to prevent polyspermy.

Question 12

State the function of mitochondria in ovum cells

Answer 12

Releases atp energy via aerobic respiration.

Question 13

State the function of a haploid nucleus in ovum cells

Answer 13

Provides half the dna required to produce a diploid nucleus, ready to be paired with the haploid nucleus of a sperm cell.

Question 14

Describe the process and function of the acrosome reaction.

Answer 14

Enzymes are released from the acrosome in vesicles, and are transported to the sperm cell membrane where they are released via exocytosis and digest the zona pellucida around the ovum cell.

Question 15

Describe the process and function of the cortical reaction.

Answer 15

Enzymes released from cortical granules catalyse reactions in the zona pellucida causing it to harden and thicken

Question 16

Give the term to describe when the haploid nuclei of the ovum and the sperm fuse

Answer 16

Fertilisation

Question 17

State the definition of the term locus

Answer 17

A point / location on the chromosome

Question 18

State the definition of the term linkage

Answer 18

Two genes in close enough proximity to one another that crossing over cannot occur between them, so they are linked to each other during meiosis

Question 19

Explain why males are more likely to suffer from X-linked diseases than females

Answer 19

Because males only have one X chromosome, so they only need one diseased allele to show phenotypes, whereas women could need 2 (if it is a recessive phenotype)

Question 20

Explain how a stem cell can differentiate into a specialised cell

Answer 20

Under certain conditions, some genes in a stem cell are activated, whilst others are inactivated

mRNA is transcribed from active genes only

This mRNA is then translated to form proteins

These proteins are responsible for modifying the cell (e.g. they help to determine the structure of the cell and the processes that occur within the cell)
As these proteins continue to modify the cell, the cell becomes increasingly specialised

The process of specialisation is irreversible (once differentiation has occurred, the cell remains in its specialised form)

Question 21

Explain how the lac operon allows differential gene expression in prokaryotes (incl. how the gene is activated and inactivated)

Answer 21

Lac operon is a process. the lactase gene can have a lac repressor bind to it which turns it off when there is no lactose present, when lactose is present and glucose is not
present, lac repressor has a high affinity for lactose and so will bind to lactose instead of lactase gene, freeing the lactase gene allowing mRNA to be transcribed from it.

Question 22

Define the term stem cell

Answer 22

A stem cell is a cell that has not differentiated into a specific function

Question 23

Define the term pluripotency

Answer 23

Pluripotent stem cells can differentiate into any cell type apart from extra embryonic cells.

Question 24

Define the term multipotency

Answer 24

multipotent stem cells can differentiate into a selection of cell types, but not all.

Question 25

Define the term totipotency

Answer 25

a totipotent stem cell can differentiate into any form of cell including extra embryonic cells

Question 26

Explain how pluripotent cells are extracted from an embryo

Answer 26

A syringe is used to extract pluripotent cells from the centre of a blastocyst

Question 27

Give the ethical arguments for and against the use of embryonic stem cells in research/medicine

Answer 27

For: allows development of medicine which could save lives,
embryos have no brain therefore have no feelings.
against: Could be considered killing a child as the embryo has to die for the stem cells to be extracted, essentially prevents a child from coming into existence

Question 28

State what an induced pluripotent stem cell (IPSC) is

Answer 28

An adult stem cell that has been genetically modified to make a pluripotent stem cell.

Question 29

Explain why IPSCs are advantageous over embryonic stem cells

Answer 29

Does not require the killing of an embryo, does not cause rejection of the new cells as the cells are from the person they will be used on so they wont have to take immune suppressants.

Question 30

What effect does methylation of a gene have on its gene expression

Answer 30

Attaches to DNA which attracts proteins which block transcription, therefore reducing its ability to be transcribed, therefore reducing the amount of protein produced in association with the gene, therefore reducing the gene expression.

Question 31

What effect does histone modification have on gene expression

Answer 31

Weakens association with histone, causing DNA to be less tightly packed, allowing it to be transcribed, causing more of that gene’s protein to be produced, therefore increasing the gene expression.

Question 32

Give the definition of a tissue

Answer 32

A collection of identical cells

Question 33

Give the definition of an organ

Answer 33

A collection of different tissues performing a specific function

Question 34

Give the definition of an organ system

Answer 34

a collection of organs which carry out many different functions e.g digestive tract.

Question 35

explain how histone modifications result in a spectrum of gene expression

Answer 35

Genes can be entirely repressed if dna has a strong association with histone as dna will be tightly wound. As histone gets more modifications, it becomes more accessible for transcription as the dna becomes more weakly associated with the histone proteins, until eventually the gene is fully activated as the dna is completely unwound.

Question 36

Explain why genetically identical twins look less similar to eachother with age

Answer 36

Due to epigenetic changes as a result of a change in their environment, causing the switching on and off of certain genes which would affect their phenotype.