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 folding

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, folding into its 3D shape 0en route. Protein is packaged in vesicles at the end of the endoplasmic reticulum and fuse to form the sacs of the Golgi Apparatus. Here proteins are modified. The protein is packaged in secretory vesicles and they are secreted through 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 what happens in the G phases of the cell cycle.

Answer 7

This is where cells grow.

Question 8

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

Answer 8

Synthesis.

Question 9

Describe what happens in interphase.

Answer 9

Organelles are synthesised and DNA replication occurs.

Question 10

Describe what happens in prophase.

Answer 10

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 11

Describe what happens in metaphase.

Answer 11

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

Question 12

Describe what happens in anaphase.

Answer 12

The centromeres split and the spindle fibres shorten.

Question 13

Describe what happens in telophase.

Answer 13

Chromosomes unravel and the nuclear envelope reforms.

Question 14

Describe what happens in cytokinesis.

Answer 14

Divides into two cells by invagination or constriction.

Question 15

What is mitosis important for?

Answer 15

Growth
Repair
Asexual reproduction.

Question 16

What is the calculation for mitotic index?

Answer 16

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

Question 17

Describe sex linkage of genes.

Answer 17

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 18

Describe totipotency.

Answer 18

Has the potential to give rise to all cell types.

Question 19

Describe pluripotency.

Answer 19

Has the ability to give rise to most cell types.

Question 20

Describe multipotency.

Answer 20

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

Question 21

Describe the epigenome.

Answer 21

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 22

Describe the lac operon experiment.

Answer 22

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 23

Define polygenic inheritance.

Answer 23

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

Question 24

Describe the production of melanin.

Answer 24

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 25

Describe nature and nurture as influences for epigenetic changes.

Answer 25

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 26

Define cancer.

Answer 26

Rate of cell multiplication is faster than cell death.

Question 27

Describe oncogenes.

Answer 27

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

Question 28

Describe tumour suppressor genes.

Answer 28

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

Question 29

Describe general risk factors for cancer.

Answer 29

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

Question 30

Sperm cell

Answer 30

Flagellum for movement
Haploid nucleus
Acrosome contains enzymes to digest the outer layer of the egg
Mid regio filled with mitochondria to provide energy for movement

Question 31

Ovum

Answer 31

Haploid nucleus
Follicle cells
Cortical granules - vesicles contains a substance that helps thicken the zona pellucida.

Question 32

Difference between chromosome and chromatin

Answer 32

Chromatin is dna wrapped around histones whereas chromosomes are visible during cell division and they are condensed dna.

Question 33

Differential gene expression

Answer 33

1- chemical stimulus
2- some genes are activated
3- activated gens are translated to form mRNA
4- mRNA is transcribed to form protein
5- protein modifies the cell into specialised form

Question 34

Acetylation

Answer 34

Allows the genes to be switched on, not wrapped around the histone

Question 35

Discontinuous variation

Answer 35

Bar graph
Discrete data
Unaffected by environment

Question 36

Continuous variation

Answer 36

Line graph
No discrete categories
Controlled by a lot of genes and environment

Question 37

Methylation

Answer 37

Wrapped around the histone, switched off a gene.

Question 38

Gene regulation

Answer 38

Is temporary whereas differential gene expression is less temporary.

Question 39

Polygenic Inheritance

Answer 39

More than one gene on more than one locus is involved in a single characteristic of an organism

Question 40

Observing mitosis.

Answer 40

Test tube of HCl placed into 60C water bath. Cut off root tip of garlic. Place in watchglass of acetic alcohol for 12 minutes . Remove then place in watchglass containing ice cold distilled water. Place tips into HCl for 5 minutes. Repeat previous steps. Transfer 1 tip to a microscope slide, add a drop of orcein ethanoic stain. Add coverslip. View under microscope.