Genetics

Question 1

What is included in the structure of the nucleus?

Answer 1

Nuclueolus
Nucleoplasm
Chromatin
Nuclear pores

Question 2

How many pairs of homologous chromosomes are there?

Answer 2

23 pairs

46 individual

Question 3

What are the four bases found in DNA

Answer 3

Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)

Question 4

What are the difference between male and female chromosomes?

Answer 4

Female chromosomes - XX
Male chromosomes - XY

Y chromosome is shorter than the X

Question 5

What is the structure of DNA

Answer 5

Double stranded molecule made up of 2 nucleotide chains.
Nucleotides consist of 3 subunits, a sugar, a phosphate group and a base.
In a double helix

The ends of the DNA strand are 5’ at phosphate end and 3’ at the deoxyribose end. They run antiparallel, this causes the twisting of the double helix structure

Question 6

What DNA nucleotides bind together

Answer 6

T - A

G - C

Question 7

What is a genome?

Answer 7

Cells in an organism contains the same genetic information in what is known as the genome.
The genome controls the biochemical activity of the cell in response to multiple stimuli.
The genome contains the inherited traits which are transmitted from generation to generation.

Question 8

Why are genes found in pairs?

Answer 8

The gene on one chromosome is matched at the locus site on the other chromosome

Question 9

How many genes does as genome contains

Answer 9

20,000 to 21,000

Question 10

What sugar is in DNA

Answer 10

Deoxyribose

Question 11

What are bases are purines and what are pyrimidines?

Answer 11

Purines = Adenine + Guanine
Pyrimidines = Thymine + Cytosine

Question 12

What type of bonding occurs between the opposite corresponding nucleotides in DNA strands?

Answer 12

Hydrogen bonding

Question 13

What is a nucleoside? And how does it become a nucleotide?

Answer 13

A sugar and base, they are bonded by the 1’ carbon of the sugar and the nitrogen at position 9 of the purines and the nitrogen at position 1 of the pyrimidines.
By adding a phosphate group it becomes a nucleotide, it is attached to the 5’ carbon of the sugar

Question 14

How are polynucleotides bonded?

Answer 14

The 5’ phosphate of one nucleotide bonds with the 3’ carbon on the next nucleotide (removing OH group in process)
The bond is a 3’-5’ phosphodiester bond

Question 15

Describe the directionality in DNA

Answer 15

The strand run antiparallel

One strand has the oxygen of the ribose above the carbons, and in the other strand, it is below

Question 16

What are histones?

Answer 16

Proteins are found in the nucleus are made up of different subunits. DNA is wrapped around the histones.
Each chromosome contains a long molecule of DNA that must fit into the cell nucleus, to do this the DNA wraps around histone proteins giving the chromosome a more compact shape.

HIstones also play a role in the regulation of gene expression.

Question 17

What is chromatin?

Answer 17

The DNA wrapped around the histones is further processed into chromatin fibres,
Large quantity of histones. Chromatin is condensed even further to chromosomes.

Question 18

What is a gene?

Answer 18

A gene is a discrete segment of DNA that encodes the amino acid sequence of a polypeptide.
A specific section that codes for proteins. This needs to be synthesized to function.
The process is transcription and translation

Question 19

How many genes are in a chromosome?

Answer 19

2x genes - 1 copy of the same from each parent

The genes are heritable factors that control a specific characteristic

Question 20

How can 2 brown eyed parents have a baby with blue eyes?

Answer 20

The two genes that control eye colour are recessive genes. Both parents have given their recessive gene that codes for blue eyes.

Question 21

What is Mitosis?

Answer 21

DNA replication

Question 22

What are the phases in Mitosis? (Cell cycle phases)

Answer 22

G1 phases - Cell growth, duplication of organelles, prep for DNA replication
S phase - DNA replication
G2 phase - Prepare to divide, final cell growth
M phase - cell division

Semi-conservative process - always one copy of DNA of mother in each cell, 50% in daughter cell, 50% newly made. 1 mother cell –> 2 daughter cells

Question 23

What are the checkpoints in mitosis? Where are they and what do they check for?G

Answer 23

G1 checkpoint:

• At end of growth phase
• Checks size and if it has proper proteins for synthesis phases
• If not it goes into resting period (G0) until its ready to divide

DNA synthesis checkpoint:

• Occurs during S phase
• Checks for correct replication

Mitosis checkpoint:

• Occurs in mitosis phase
• Checks if its complete
• If so cell divide and cycle repeats

Question 24

What is the process of transcription

Answer 24

• Transcriptor factors bind to the promoter region of the gene to stimulate the start of transcription.
• Enhancers bind to enhance transcription, they can bind either to the transcription factors or to the gene anywhere before the promotor region.
• DNA polymerase binds to the TATA box which is a region of the gene that is rich A and T bases, these bases only contain 2 hydrogen bonds so are easier to separate.
• DNA polymerase causes the DNA strand to ‘unzip’, from the TATA box it moves along to strand until it reaches the initiation stage (beginning of the part of the gene that is going to be copied)
• DNA polymerase moves along the strand from the 5’ to the 3’ end
• Adding free RNA nucleotides to the corresponding bases, joining the nucleotides with phosphodiester bonds
• When it reaches the stop site of the gene, DNA polymerase zips the DNA dissociates from the strand and the mRNA/ pre-mRNA strand is released
• In eukaryotic cells mRNA needs to undergo splicing, before it can leave the nucleus. This is pre-mRNA, which contains exons and introns. Exons code for proteins and intron do not, so splicing removes the introns and joins the exons together with phosphodiester bonds. Now mRNA is formed and can leave the nucleus into the cytoplasm

Question 25

What is the process of translation?

Answer 25

• mRNA leaves the nucleus and travels in the cytoplasm and binds to ribosomes on the rough endoplasmic reticulum.
• It binds at the start codon, where the ribosome then reads the triplet code of the first three nucleotides on the mRNA strand and a tRNA molecule brings the corresponding bases to the codon, called the anticodon. The tRNA molecule also has the coding amino acid bound to it.
• The process repeats for the next codon and the 2 amino acids break off and join together by a peptide bond, which is an active process requiring ATP and an enzyme.
• The process is repeated, the ribosome moves along the mRNA stand causing tRNA molecules to bring the corresponding bases and the protein, to create the formation of a polypeptide chain.
• The process stops when a stop codon is reached on mRNA.
• Protein synthesis is the complete

Question 26

Describe the process of DNA replication

Answer 26

• Helicase unwinds and unzips the strands and forms a replication fork
• Each strand provide a template for new strand of DNA
• The strands run antiparallel, there is a leading strand which runs in 5’ to 3’ and a lagging strand which runs in 3’ to 5’ direction.
• In replication of the leading strand, the enzyme primase forms an RNA primer on the strand marking the starting point of replication
• DNA polymerase binds to the primer and move along the strand and adds corresponding nucleotides one at a time continuosly
• In replication of the lagging strand, it is done differently as DNA polymerase can only move in the 5’ to 3’ direction. It goes about this by building the new strand in small sections called okazaki fragments
• Each fragment is started with an RNA primer and DNA polymerase adds a short row of corresponding bases to the section
• Another primer is added to the next section, and the process is repeated until the full strand is replicated and DNA polymerase reaches the end
• Exonuclease removes all primers from both strands of DNA
• DNA polymerase fills in the gaps left behind
• DNA ligase seals up the DNA fragments in both strands to form a continuous double strand.
• DNA replication is now complete and there should be 2 identical daughter cells. These cells are semi conservative as the contains 50% of DNA from their mother cell and 50% of new DNA.