Lecture 1 - Genome Organisation

Question 1

What is the genome size of a virus

Answer 1

1776 base pairs to 1.2 million bp

Question 2

What is the genome size of a prokaryote

Answer 2

112,000 bp to 13.6 million bp

Question 3

What is the genome size of a eukaryote

Answer 3

2.3 million bp - 148.8 billion bp

Question 4

What is the genome size of a human

Answer 4

3.1 billion bp

Question 5

How is a genome organised in a prokaryote

Answer 5

Relatively small - 1-2 micrometers in length
Not contained in a nucleus
Circular DNA with a single origin of replication forms a nucleoid
Typically 500-10,000 genes
Dense - eg. 90% protein coding genes
Also contains plasmid DNA

Question 6

How does bacterial genome replication occur

Answer 6

Starts at single origin of replication (Ori)
Forms replication forks
Splits eventually into 2 loops, each containing one original and one new strand of DNA (Semi-conservative rep)
(Page 13)

Question 7

What are bacterial plasmids

Answer 7

Small circular DNA molecules with a few genes

Question 8

What do plasmids allow bacteria to do

Answer 8

Horizontal Gene transfer (HGT)

Question 9

What is HGT

Answer 9

Exchanging DNA between unrelated bacteria using plasmids - eg. allows the genes for antibiotic resistance to be passed on

Question 10

What is supercoiling of DNA

Answer 10

Amount of twisting in a DNA molecule

Question 11

What are the two types of DNA supercoiling

Answer 11

Overwound and Underwound

Question 12

What are Topoisomerases

Answer 12

DNA unwinding enzymes

Question 13

What do the two Types of Topoisomerase do

Answer 13

Type 1 - Cleave 1 strand of a double helix - unwinds supercoils

Type 2 - Cleaves 2 strands of a double helix, introduces supercoils

Question 14

What is a Nucleoid

Answer 14

Supercoiled DNA held together by Nucleoid Associated Proteins (NAPs) so that it uses less space

Question 15

How is a genome in a eukaryote genome organised

Answer 15

Much larger than prokaryote - 10-100 micrometres
Nuclear envelope
Linear Chromosomes, multiple organs of replication with telomeres at each end
5000-30,000 genes
Large amounts of non-coding DNA (Introns and repeats) eg. 97.5% non-coding DNA
Packed to form Protein-DNA complexes called chromatin

Question 16

Why is there such variation in eukaryotic genome length

Answer 16

Number of non-coding regions

Question 17

What is Polyploidy and what organisms does it occur in

Answer 17

Where the whole genome is copied, meaning an individual can possess more than two complete sets of chromosomes (even 6 copies of the same chromosome)

Occurs in plants, and occasionally fish and amphibians

Question 18

How may origins of replication does a human have

Answer 18

30,000-50,000

Question 19

What advantage does having many origins of replication have for a eukaryote

Answer 19

Allows eukaryotes to be more complex

Question 20

What advantages does having a slow replication time (10x slower than prokaryotes) have for a eukaryote

Answer 20

Allows proof reading of work for high fidelity

Question 21

How big is a eukaryotic nucleus

Answer 21

6 micrometers in diameter

Question 22

What is chromatin formed from

Answer 22

DNA wraps into a histone protein to form a nucleosome (8 histones with 150 bp wrapped round)
(page 24)

Question 23

Lecture Link

Answer 23

https://uniofbath.cloud.panopto.eu/Panopto/Pages/Viewer.aspx?id=3c8b81d1-0b67-4bb4-89b5-b20600794d05

Question 24

How are human chromosomes set out

Answer 24

22 homologous pairs, 1 set of sex chromosomes (46 chromosomes)

Question 25

What does a centromere do in a metaphase chromosome

Answer 25

Contains Alpha Satellite DNA - 171 base pair sequence repeated near each centromere around 18,000 times
Site of a Kinetochore - attaching site for microtubules to pull chromatids apart

Question 26

What are telomeres and what do they do

Answer 26

Repetitive DNA sequences at the end of chromosomes

Acts as a protective cap to protect chromosomes from degradation and fusion by binding to proteins to make structure called shelterin

Question 27

Why do cells age

Answer 27

Telomeres get shorter leading to chromosomal degradation

Question 28

What is some evidence that supports the endosymbiosis theory fro Mitochondria and Chloroplasts

Answer 28

Contains loops of its own DNA
Cyanobacteria looks similar to chloroplasts
mtDNA is similar to prokaryotic DNA
mt segregate randomly among daughter cells

Question 29

Describe the rough process of Endosymbiosis

Answer 29

Anaerobic eukaryotic cell engulfed aerobic eubacteria/cyanobacteria (depending on mitochondria or chloroplast)

Eukaryotes evolved containing eubacteria/cyanobacteria

Forms chloroplast and mitochondria

Question 30

How are chloroplast and mitochondrial genes inherited

Answer 30

Exclusively from maternal line

Question 31

What are the features of mitochondrial genome

Answer 31

16000 bp
no untranslated areas
single promoter per strand (like prok)
Two long transcripts are cleaved
Codes for 13 proteins and 24 RNAs

Question 32

What use does studying Mitochondrial DNA have

Answer 32

mtDNA only inherited from mother
mtDNA is conserved but naturally accumulates mutations over time
Used to trace human maternal lineageW

Question 33

Who was Mitochondrial Eve

Answer 33

Most recent common ancestor found via mtDNA
150,000-200,000 years ago in East Africa
(support the “out of Africa” theory”)