Lecture 1 - Genome Organisation Flashcards
What is the genome size of a virus
1776 base pairs to 1.2 million bp
What is the genome size of a prokaryote
112,000 bp to 13.6 million bp
What is the genome size of a eukaryote
2.3 million bp - 148.8 billion bp
What is the genome size of a human
3.1 billion bp
How is a genome organised in a prokaryote
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
How does bacterial genome replication occur
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)
What are bacterial plasmids
Small circular DNA molecules with a few genes
What do plasmids allow bacteria to do
Horizontal Gene transfer (HGT)
What is HGT
Exchanging DNA between unrelated bacteria using plasmids - eg. allows the genes for antibiotic resistance to be passed on
What is supercoiling of DNA
Amount of twisting in a DNA molecule
What are the two types of DNA supercoiling
Overwound and Underwound
What are Topoisomerases
DNA unwinding enzymes
What do the two Types of Topoisomerase do
Type 1 - Cleave 1 strand of a double helix - unwinds supercoils
Type 2 - Cleaves 2 strands of a double helix, introduces supercoils
What is a Nucleoid
Supercoiled DNA held together by Nucleoid Associated Proteins (NAPs) so that it uses less space
How is a genome in a eukaryote genome organised
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
Why is there such variation in eukaryotic genome length
Number of non-coding regions
What is Polyploidy and what organisms does it occur in
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
How may origins of replication does a human have
30,000-50,000
What advantage does having many origins of replication have for a eukaryote
Allows eukaryotes to be more complex
What advantages does having a slow replication time (10x slower than prokaryotes) have for a eukaryote
Allows proof reading of work for high fidelity
How big is a eukaryotic nucleus
6 micrometers in diameter
What is chromatin formed from
DNA wraps into a histone protein to form a nucleosome (8 histones with 150 bp wrapped round)
(page 24)
Lecture Link
https://uniofbath.cloud.panopto.eu/Panopto/Pages/Viewer.aspx?id=3c8b81d1-0b67-4bb4-89b5-b20600794d05
How are human chromosomes set out
22 homologous pairs, 1 set of sex chromosomes (46 chromosomes)
What does a centromere do in a metaphase chromosome
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
What are telomeres and what do they do
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
Why do cells age
Telomeres get shorter leading to chromosomal degradation
What is some evidence that supports the endosymbiosis theory fro Mitochondria and Chloroplasts
Contains loops of its own DNA
Cyanobacteria looks similar to chloroplasts
mtDNA is similar to prokaryotic DNA
mt segregate randomly among daughter cells
Describe the rough process of Endosymbiosis
Anaerobic eukaryotic cell engulfed aerobic eubacteria/cyanobacteria (depending on mitochondria or chloroplast)
Eukaryotes evolved containing eubacteria/cyanobacteria
Forms chloroplast and mitochondria
How are chloroplast and mitochondrial genes inherited
Exclusively from maternal line
What are the features of mitochondrial genome
16000 bp
no untranslated areas
single promoter per strand (like prok)
Two long transcripts are cleaved
Codes for 13 proteins and 24 RNAs
What use does studying Mitochondrial DNA have
mtDNA only inherited from mother
mtDNA is conserved but naturally accumulates mutations over time
Used to trace human maternal lineageW
Who was Mitochondrial Eve
Most recent common ancestor found via mtDNA
150,000-200,000 years ago in East Africa
(support the “out of Africa” theory”)
