chromosome structure

Question 1

at what phase can individual chromosomes be distinguished

Answer 1

metaphase of mitosis

Question 2

in what mitotic phase are subnuclear territories of chromosomes organised

Answer 2

interphase

Question 3

organisation of chromosomes in interphase

Answer 3

• coiled chromatin in 2 forms
  
  • thick fibre = highly coiled
  • beads on string = pre-coil
    
    • made up of nucleosomes with DNA wrapped round

Question 4

what are nucleosomes

Answer 4

DNA coiled round histones
exist in pairs = 8 core subunits
produce cylindrical shape with DNA helix wound round

Question 5

function of histone tails

Answer 5

tailes pretrude out of nucleosome and interact with proteins in free space of nucleus to aid transcription and translation = regulates structure of chromatin

Question 6

features of the linker histone (H1)

Answer 6

• strap shaped
• interacts with helix surrounding nucleosome
• establishes transcriptionally silent regions = not needed for PS
• rich in lysine and arginine = basic
  
  • binds to DNA readily but not sequence specific = binds to phosphate backbone

Question 7

how is DNA packaged by chromatin

Answer 7

DNA is packaged by histone octamers into compact flexible 30nm chromatin scaffold that can be remodelled to accomodate protein complexes

Question 8

role of histones

Answer 8

• keeps DNA packed tightly in chromosomes
• be flexible

Question 9

role of DNA remodelling enzymes

Answer 9

• remove nucleosomes
• opens up DNA sequence allowing transcription or replication proteins can bind

Question 10

what are telomeres

Answer 10

• single stranded 3’ overhangs at end of chromosomes
• protect endochromosomes from multiple replications - genetic info would be lost
• 10-100 nucleotides long

Question 11

what are centromeres

Answer 11

• regions of repeated DNA where chromosomes are connected via mitotic spindle during mitosis
• centromeres bind to kinetochore = stabilisation of spindle = lines up and segregate properly
• contain alpha satellite DNA repeats that form condensed chromatin with histone octamers containing unusual subunits

Question 12

what are kinetochores

Answer 12

complex of proteins associated with centromere, where microtubules attach

Question 13

kinetochore structure

Answer 13

• made up of inner and outer plate
• inner plate proteins bind to chromatin containing alpha-satellite DNA
• outer plate proteins bind to protein components of mitotic spindle = microtubules
• outer plate fits on top of inner plate to allow microtubules to bind

Question 14

role of H3 histone in yeast

Answer 14

binds to inner plate and outer plate forms ring round microtubules to allow specific binding

Question 15

types of transposons

Answer 15

DNA transposons
retroviral-like transposons
non-retroviral polyA transposons

Question 16

what are DNA transposons

Answer 16

• encode transposase = move around genome via cut and paste
• can result in broken chromosomes and insert in important genes = mutagenic

Question 17

what are retroviral-like transposons

Answer 17

• similar mechanism to viral spread
• use reverse transcriptase
• DNA → RNA → DNA

Question 18

what are transposons

Answer 18

• class of genetic elements that can “jump” to different locations within a genome
• most copies of these in genome are defective and ancient versions of formerly functional elements with many mutations that prevent expression of functional proteins

Question 19

how do non-retroviral polyA transposons work

Answer 19

• dont need virus capsid to transcribe rna back to dna so insert into dna
• synthesise rev transcriptase → RNA with poly A tail
• ## cuts DNA then RNA → DNA at that location e.g L1 transcription