Voice of the Genome

Question 1

Compare and contrast prokaryotes and eukaryotes.

Answer 1

Prokaryotes are smaller than eukaryotes.
Prokaryotes do not contain membrane bound organelles whereas eukaryotes do.
Smaller ribosomes in prokaryotes.
Prokaryotes have a flagellum whereas eukaryotes do not.

Question 2

What is the calculation for magnification?

Answer 2

Magnification = image size divided by actual size.

Question 3

Describe protein synthesis.

Answer 3

DNA is transcribed in mRNA. The mRNA leaves the nucleus. Proteins made on ribosomes enter the rough endoplasmic reticulum. Protein moves through the endoplasmic reticulum, becoming 3D en route. Vesicles containing the protein pinch off of the endoplasmic reticulum and fuse to form the sacs of the Golgi Apparatus. Here proteins are modified. The vesicles are pinched off of the Golgi Apparatus and fuse with the cell surface membrane. The proteins are released via exocytosis.

Question 4

Describe fertilisation.

Answer 4

The sperm reach the ovum. Chemicals are released, triggering the acrosome reaction. The acrosome fuses with the membrane and releases enzymes which digest the corona radiata and the zona pellucida. The sperm fuses with the ovum. Enzymes are released from cortical granulez which thicken the zona pellucida, preventing polyspermy. The nuclei fuse.

Question 5

Describe independent assortment.

Answer 5

Either chromosome from each pair could be in any gamete.

Question 6

Describe crossing over.

Answer 6

Homologous chromosomes pair up and the four chromatids come into contact. The chromatids break at the chiasma and rejoin in any variation.

Question 7

Describe fertilisation in plants.

Answer 7

Female gametes are produced in the ovary. In the anther, cells divide to produce pollen grains. Two haploid nuclei are produced in the pollen grain. Fertilisation occurs in the ovule. The pollen grain germinates on the style, forming a pollen tube. The nucleus in the pollen grain divides to form two haploid nuclei which move through the pollen tube. The tube enters the ovule. One nucleus fuses with the egg cell to form a diploid nucleus. The other fuses with two nuclei in the embryo forming a triploid cell. This divides to form the endosperm.

Question 8

Describe what happens in the G phases of the cell cycle.

Answer 8

This is where cells grow.

Question 9

Describe what happens in the S phase of the cell cycle.

Answer 9

Synthesis.

Question 10

Describe what happens in interphase.

Answer 10

Organelles are synthesised and DNA replication occurs.

Question 11

Describe what happens in prophase.

Answer 11

Chromosomes become shorter and thicker. They are joined at the centromere. Microtubules form spindle fibres. Centrioles move to opposite poles. Nuclear envelope breaks down.

Question 12

Describe what happens in metaphase.

Answer 12

Centromeres attach to spindle fibres and the chromosomes line up down the middle.

Question 13

Describe what happens in anaphase.

Answer 13

The centromeres split and the spindle fibres shorten.

Question 14

Describe what happens in telophase.

Answer 14

Chromosomes unravel and the nuclear envelope reforms.

Question 15

Describe what happens in cytokinesis.

Answer 15

Divides into two cells by invagination or constriction.

Question 16

What is mitosis important for?

Answer 16

Growth
Repair
Asexual reproduction.

Question 17

What is the calculation for mitotic index?

Answer 17

(Prophase + Metaphase + Anaphase + Telophase) divided by the total number of cells.

Question 18

Describe sex linkage of genes.

Answer 18

Genes for a certain characteristic are on the sex chromosome.

If the characteristic is on the X chromosome, males will be sufferers as they only need one copy of the allele. In order for females to be sufferers, they would need to have both copies of the recessive allele.

Question 19

Describe totipotency.

Answer 19

Has the potential to give rise to all cell types.

Question 20

Describe pluripotency.

Answer 20

Has the ability to give rise to most cell types.

Question 21

Describe multipotency.

Answer 21

More differentiated buy still has the ability to give rise to cells of their type.

Question 22

Describe the epigenome.

Answer 22

The epigenome influences which genes are transcribed. DNA is wrapped around histones which are surrounded by chemical markers. Modification of histones occurs by methylation or acetylation which affects how tightly the DNA is wrapped. The more tightly wound causes genes to become inactive and switched off.

Question 23

Describe the lac operon experiment.

Answer 23

E. Coli produces beta galactosidase to break down carbohydrate lactose. This converts lactose to its monosaccharides, glucose and galactose.
When lactose is not present, a lactose repressor binds to DNA, preventing the production of beta galactosidase, RNA polymerase is unable to bind to the DNA.

Question 24

Define polygenic inheritance.

Answer 24

More than one gene is involved in the inheritance of a single characteristic.

Question 25

Describe changes around height.

Answer 25

Taller men have more children.
Greater movement.
Less inbreeding.
Better nutrition and improved health.
End of child labour.
Better heating.
Better clothing.

Question 26

Describe the production of melanin.

Answer 26

Made in melanocytes which is activated by melanocyte-stimulating hormones. Melanocytes move melanin into melanosomes which are then transferred into skin and hair cells.

Question 27

Describe colour in animals.

Answer 27

Tyrosinase catalyses tyrosine into melanin. Animals such as Himylayan rabbits and Siamese cats have mutated alleles for tyrosinase. The enzyme is unstable and inactivated at normal body temperature. This results in darker coloured paws, tail and ears.

Question 28

Describe nature and nurture as influences for epigenetic changes.

Answer 28

Nature: environment can trigger changes, such as medicines or drugs.

Nurture: behaviour can have an effect on whether a gene is expressed.
A “good” mother and a “bad” mother switch offspring (baby rabbits). The good mother is high in grooming, which leads to no methylation, which expresses a gene. The bad mother is low in grooming, which results in methylation and the gene is not expressed.

Question 29

Define cancer.

Answer 29

Rate of cell multiplication is faster than cell death.

Question 30

Describe oncogenes.

Answer 30

Oncogenes code for proteins stimulating transition in the cell cycle. Mutations in oncogenes may lead to excessive or quicker cell division.

Question 31

Describe tumour suppressor genes.

Answer 31

Produces suppressor proteins which stop the cycle. Loss of tumour suppressor proteins has been linked with different variations of cancers.

Question 32

Describe general risk factors for cancer.

Answer 32

Genetic predisposition
Smoking
Exposure to UV light
Poor diet
Viral infections
Exposure to asbestos.