Chromosomes

Question 1

LO:
Understand how DNA is packaged into chromatin and describe the structure and function of histones.

Understand that chromosome structure changes at different phases of the cell cycle.

Understand the structure-function relationships of telomeres, centromeres, replication origins and kinetochores.

Understand that non-protein-coding DNA exists in the genome and be able to describe characteristics of repeated DNA elements.

Describe the different types of eukaryotic transposable elements and their replication and transposition mechanisms.

Answer 1

1

Question 2

SIMPLY- what does packing DNA into chromatin fibres enable?

Answer 2

SELECTIVE gene expression
replication and transmission of the genome to progeny cells

Question 3

Each chromosome pair differs in …. and DNA ……..

Answer 3

size and sequence

Question 4

From interphase nuclei, and beyond, how do individual chromosomes occupy the nucleus

Answer 4

with distinct subnuclear territories (google what this means)

Question 5

what is a chromosome in terms of chromatin formation

Answer 5

highly coiled fibre of chromatin

Question 6

using EM, interphase chromatin resembles ‘beads on a string’- what are the beads called

Answer 6

nucleosomes

Question 7

how many histone complexes will make up a nucleosome

Answer 7

~ 8 histones per nucleosome

Question 8

what do the N-terminals from the histones interact with? and what do these interaction facilitate?

Answer 8

1. free to interact with other proteins
2. facilitates REGULATION of chromatin STRUCTURE and FUNCTION.

Question 9

Name of the linker histone that straps DNA onto histone octamers?

Answer 9

H1

Question 10

what do the H1 or linker histones do to DNA thats attached?

Answer 10

limits movement relative to the H1 module

Question 11

what is the result of the H1 histone complex on transcription?

Answer 11

general repressor o transcription

Question 12

what is the size of the chromatin scaffold

Answer 12

30nm

Question 13

definition of chromatin

Answer 13

DNA and proteins packaged together

Question 14

simply what are fractal globules

Answer 14

1. globules within globules
2. they can reversibly condense and decondense without becoming knotted

Question 15

specialised DNA sequences in chromosomes facilitate….
1. simple
2. harder- duplicated parts

Answer 15

1. reliable and complete replication
2. segregation of duplicated chromosomes during division

Question 16

definition of telomeres

Answer 16

specialised repetitive DNA sequences at chromosome ends

Question 17

what are telomeres replicated by
1- simple
2- name of it

Answer 17

1. specialised DNA polymerase
2. called Telomerase

Question 18

Part I
role of Alpha-satellite DNA in cell division
-centromeres

Answer 18

1. centromeres contain A-S DNA repeats, readily form condensed chromatin

Question 19

Part II
Kinetochore, inner and outer plate
inner plate binds to ..
outer plate binds to…

Answer 19

1. inner plate proteins bind to chromatin containing A-S DNA
2. Outer plate proteins bind to components of mitotic spindle- i.e microtubules

Question 20

In yeast-
what does the kinetochore link a single nucleosome of CENTROMERIC chromatin to?

Answer 20

a single microtubule

Question 21

what are transposons and what do they do?

Answer 21

they are mobile genetic elements that ‘jump’ around the genome
- transposable elements

Question 22

3 different types of transposons?
1. simple
2. viral
3. PolyA

Answer 22

1. DNA transposons
2. Retroviral Transposons
3. Non-retroviral PolyA transposons

Question 23

how do DNA transposons ‘jump’

Answer 23

move by a cut-and-paste mechanism w/o self-duplication
req- transposon-encoded enzyme TRANSPOSASE

Question 24

do it
Finnegan DJ (2012) Curr. Biol. 22: R432-R437.

Answer 24

now

Question 25

replication of other transposable elements- like retrotransposons

Answer 25

-using RNA intermediates- producing new DNA copies -They integrate at new genomic locations -USING self-encoded Reverse transcriptase

Question 26

examples of retrotransposons TY TY EVR

Answer 26

Ty1-copia Ty3-gypsy ERV elements

Question 27

what do retrotransposons not fully encode

Answer 27

they don't fully encode ACTIVE infectious viruses

Question 28

sequence of replicating 'other transposable elements' (5) (1. RNA and cell, 2. self-encode role, 3. new DNA, 4/ 5. leading to protein gain

Answer 28

1. Entry of RNA intermediate into the cell-> loss of the envelope 2. Self encoded reverse transcriptase makes RNA-> RNA/ DNA-> DNA/ DNA double helix 3. copy of the DNA integrated into host chromosome 4. transcription- many RNA copies 5. Translation= making specific proteins for new cells- capsid protein, Envelope protein, Reverse transcriptase

Question 29

Non-retroviral

Answer 29

PolyA retrotransposons- abundant in vertebrates

Question 30

integrated PolyA transposon -L1 element- what is the next stage 1,2,3,4

Answer 30

L1 RNA synthesis- obtain a strand of L1 RNA

Question 31

SUMMARY- simple effectiveness of chromatin and nucleosomes

Answer 31

1. reversible unfolding and compaction- allowing gene transcription and DNA rep Package DNA into small volume of nucleus, allow faithful segregation of genome for daughters

Question 32

SUMMARY 2- SIMPLE telomeres centromeres

Answer 32

1. prevent the loss of DNA sequences from chromosomal ends 2. mediate chromosome attachment to the mitotic spindle via kinetochore

Question 33

SUMMARY 3- simple Transposable elements

Answer 33

-Genomes of more complex organisms also have huge numbers of repeated DNA sequence elements CCCAAAGGG etc

Question 34

SUMMARY 4- DNA transposons, retroviral transposons, and polyA retrotransposons

Answer 34

all are mobile genetic transposable elements- repeated sequences- defective versions make up over half of the human genome