Chromosomes, Genes and DNA

Question 0

Describe solenoid structures

Answer 0

Fibres compacted into several hierarchal loops to create highly condensed structures - chromosome visible under light microscope in nucleus during cell division. Genes cannot be expressed when solenoid (heterochromatin)

Question 1

What are histones?

Answer 1

Proteins around which DNA molecules are wrapped. Positively charged in order to be complementary to negative P groups on DNA.

Question 2

Which bonds link nucleotides?

Answer 2

Phosphodiester bonds

Question 3

Distinguish between purines and pyrimidines

Answer 3

Purines - two ring structure e.g. G and A

Pyrimidines - one ring structure e.g. T, C and U

Question 4

Number and type of bonds between nitrogenous bases?

Answer 4

A-T has two bonds, C-G has three bonds, A-U has two bonds. H bonds between them all

Question 5

Which base pairs are responsible for major and minor grooves?

Answer 5

G and C

Question 6

Outline the cell cycle

Answer 6

G1 - cell prepares for DNA replication
S - DNA replication
G2 - cell prepares for cell division (double checking DNA)
M - cell division (mitosis)
G0 - cell just performing its normal function

Question 7

What does dNTP stand for?

Answer 7

Deoxyribonucleoside triphosphate

Question 8

In which direction does DNA replication occur?

Answer 8

5’ to 3’ end

Question 9

What does mitosis result in?

Answer 9

Two genetically identical daughter cells (identical chromosomal content)

Question 10

What does meiosis result in?

Answer 10

Four genetically different haploid cells

Question 12

Describe initiation in DNA replication

Answer 12

Recognition of origin of replication, DNA polymerase recruited alongside some other proteins, kick start by primase

Question 13

Describe elongation in DNA replication

Answer 13

Moving replication forks, helicase unwinds double helix, DNA polymerase extends 3’ end only, DNA ligase joins fragments

Question 13

How does variation arise in meiosis?

Answer 13

Independent assortment of chromosomes and crossing over

Question 14

Describe termination in regards to DNA replication

Answer 14

DNA ligase joins final fragments, chromosome number stays the same, one replicated chromosome consists of the two sister chromatids

Question 15

What is the main difference between spermatogenesis and oogenesis?

Answer 15

Spermatogenesis results in 4 sperm cells whereas oogenesis results in 1 mature ovum and 3 polar bodies

Question 16

Draw out pedigree symbols

Answer 16

Square - male, circle - female, filled - affected, unfilled - unaffected, half filled/dot - carrier, diamond - unknown gender, diagonal line through - deceased

Question 17

Describe characteristics of autosomal recessive traits

Answer 17

Heterozygotes are unaffected, males and females equally affected, 25% chance of affected offspring, two affected individuals will have affected offspring only, can skip generations, both parents have to be carriers e.g. CF

Question 18

Describe the characteristics of autosomal dominant conditions

Answer 18

Heterozygotes are affected, males and females are affected equally, rarely found in homozygous state - too severe and sufferers die, every affected individual will have at least one affected parent, disease cannot skip generations

Question 19

Describe the characteristics of X-linked conditions

Answer 19

Hemizygous males and homozygous females are affected, more common in males, heterozygous female carrier has 50% chance of getting, affected males cannot pass trait onto sons, daughters of affected males are heterozygous

Question 21

What is linkage?

Answer 21

When genes on different chromosomes show independent assortment during meiosis - if two genes are close together then they can become linked and co-segregate

Question 22

What is the RNA stem-loop structure?

Answer 22

Single stranded RNA loops back on itself, thus one side will run anti parallel and H bonds will form between complimentary bases

Question 23

Describe the key features of DNA double helix

Answer 23

2 independent polymers, complementary, anti-parallel, one complete turn in 10 bases, 0.34nm space between base pairs, purine and pyrimidines are planar and unsaturated, major and minor grooves

Question 24

Describe mitotic chromosomes

Answer 24

Highly condensed fibres. Unexpressed genomes - cannot replicate

Question 25

Describe interphase chromosomes (chromatin)

Answer 25

De-condensed. Genomes is expressed therefore can replicate

Question 26

Briefly describe the process of DNA replication

Answer 26

Initiation - recognition of origin of replication, helicase unravels double helix, primase required
Elongation - leading strand replicated from 5’ to 3’. Lagging strand - Okazaki fragments - ligase from OH to P group covalently.
Termination - 2 facing replication forks meet, ligase

Question 27

Outline the cell cycle

Answer 27

G1 - preparation for replication/growth, S - DNA replication, G2 - cell prepares for division, M - cell division (mitosis)