Voice of the Genome

Question 1

Approx. how many genes does a human have?

Answer 1

20K - 25K

(thousands)

Question 2

What is the function of genes?

Answer 2

They provide the instruction manual to build the organism from the unspecialised cells to the specialised which make up the systems, etc.

Question 3

What are prokaryotic cells?

give example

Answer 3

E.g., bacteria, cyanobacteria

• cell wall
• no nuclei
• DNA floats in cytoplasm
• no other membrane bound organelles

Question 4

Describe eukaryotic cells?

Answer 4

membrane bound organelles

nucleus

don’t all have a cell wall (have a membrane instead)

Question 5

What is the function of the mitochondria

Answer 5

the site of later stage respiration

Question 6

what do centrioles do?

Answer 6

every cell as a pair of centrioles

these are hollow protein cylinders that assist in the formation of the spindles in cellular division as well as transport within the cell

Question 7

what do lysosomes do?

Answer 7

spherical sacks

break down unwanted structures in the cell

also help to destroy old cells

Question 8

what is the functiono of the Golgi complex?

Answer 8

Modify proteins and packs them up in vesicles for transport

Question 9

Function of smooth endoplasmic reticulum?

Answer 9

Makes lipids and steroids

Question 10

what does the membrane do?

Answer 10

partially permeable barrier allowing some nutrients and gases in/out

Question 11

what do ribsomes do?

Answer 11

Float around the cytoplasm synthesising proteins

Question 12

Rough endoplasmic reticulum

Answer 12

rough - b/c ribosomes attacked on the membrane

proteins are made on the ribosomes to be transported through the ER to other parts of the cell

Question 13

What’s the nucleolus?

Answer 13

Dense body within the nucleus where ribosomes are made

Question 14

What is the function of the nucleus?

Answer 14

Contains the cell’s chromosomes and nucleolus

Chromosomes made of DNA contain gense that control protein synthesis

Question 15

Describe the process of proteins out of a cell

Answer 15

DNA transcribed into mRNA

1. mRNA leaves nucleus
2. Protein made on ribosomes enter rough endoplasmic reticulum
3. proten moves through the ER forming 3D shape
4. proteins packaged in vesicles off the ER
5. the vesicles fuse to form flattened sacs of the Golgi complex
6. proteins are modified within the Golgi
7. vesicles pinched off Golgi
8. vesicles fuse with cell surface and release protein out of cell

Question 16

What are gametes?

Answer 16

The sex cells - sperm, ova

Question 17

What does an ovum contain?

Answer 17

protein and lipid food reserves for the developing embryo

it is surrounded by the zona pellucida (jelly-like covering)

Question 18

Explain fertilisation of sperm and ova

Answer 18

1. Sperm use flaggelum to swim to ovum powered by their mitochondria
2. Sperm are attracted by the ovum’s chemicals it releases
3. On oval contact: the acrosome in the head of a sperm swells and releases digestive enzymes to break down the ovum’s zona pellicida (the acrosome reaction)
4. Once the sperm fuses and penetrates the ovum, the zona pellucida then thickens to prevent other wannabee babies - ‘corticol reaction’

Question 19

What are homologous chromosomes?

Answer 19

A pair of chromosomes with the same gene sequence, loci, chromosomal length, and centromere location.

Question 20

What is special about gametes?

Answer 20

They contain only 1/2 the normal full set of chromosomes

(23 in humans)

AKA - haploid, rather than diploid

Question 21

How are gametes formed?

Answer 21

During meiosis, occuring in ovaries and testes

In meiosis cell division there is

independent assortment

only one chromosome from each pair ends up in a gamete

this is a source of genetic variation, a random process

b/c either chromosome could be in the gamete

hence in fertilisation the possible combination of chromosomes is large (three homologous pairs could form 2³ combinations)

and crossing over

when homologous chromosomes join together as pairs, all four chromatids come into contact

at the contact points, the chromatids break (at a chiasma, cross) and rejoin exchanging sections of DNA creating a wide range of variation

Question 22

What is genetic linkage?

Answer 22

The idea that certain characteristics tend to be inherited together as the genes have a locus on the same chromosome and will hence tend to be passed on as a pair to the same gamete

e.g., hair colour and eye colour

Question 23

What are sex-linked conditions?

Answer 23

genetic conditions passed on via the two sex chromosomes

(XX female, XY male)

E.g., red-green colour and haemophilia blindness afffects mainly men

Question 24

How is red-green colour blindness passed on?

Answer 24

The gene loci for the three colour cone cells in the eye are found on the X sex chromosome

During meiosis, there can be a mutation of one of the cone pigment genes

E.G.> Emily is heterozygous for colour blindness, X^NXⁿ

• X^N= X chromosome with a normal allele for cone pigment
• Xⁿ= X chomosome with a mutant allele for cone pigment
• Emily has normal vision, but mates with Greg who has X^NY; (Y does not have a place for the cone pigment, so is empty)
• PUNNET SQUARE analysis
• Emily offers: X^NXⁿ
• Greg offers: X^NY
• or (X^NXⁿ)(X^NY) = X^NX^N; X^NXⁿ; X^NY, XⁿY
• Leaving us with 50% chance of full vision in offspring
• 25% chance of a boy with full colour vision (X^NY) and
• 25% chance of a boy who is colour blind (XⁿY)

Question 25

What is the process of plant fertilisation?

Answer 25

Ova are produced in an ovary but only one of the four nuclei at the end of meiosis forms an ovum

Inside the anther, cells divide to produce pollen grains containing male gamete nuclei

In male plants, the four haploid cells produced in meiosis undergo another mitosis division in which each nucleus divides to give two haploid nuclei in a pollen grain

Fertilisation takes place in the ovule - pollen germinate on the style and grown down towards the ovary, a process controlled by one of its haploid cells, while the other haploid nucleus divides to form two new haploid nuclei that move down the pollen tube

The tube grows through a microscopic pore into the embryo sac in the ovule, and the two male gametes enter the sac

1 male gamete fuses with the egg cell -> diploid zygote forms

1 male gamete fuses with two nuclei in the embyronic sac called polar nuclei to form a triploid cell, which then divides to form endosperm (the seed’s storage tissue)

Phew.