CHROMOSOME STRUCTURE

Question 1

Individual chromosomes can be easily distinguished at what phase of mitosis?

Answer 1

Metaphase

Question 2

What method can be used to visualise chromosomes?

Answer 2

Chromosome painting.

Question 3

Each chromosome pair differs in what?

Answer 3

DNA sequence content

Size

Question 4

What is a karyotype?

Answer 4

An organised representation of all of the chromosomes in a eukaryotic cell at metaphase.

Question 5

What can karyotyping be used for?

Answer 5

Can be used to find abnormalities.

Question 6

What does an interphase nucleus look like?

Answer 6

An interphase nucleus is a large mass of chromosomes in an organised manner. Individual chromosomes occupy distinct subnuclear territories.

Question 7

What is a chromosome?

Answer 7

A highly coiled fibre of chromatin.

Question 8

What can chromatin alternate between?

Answer 8

10nm coiled fibre and 30nm coiled fibre

Question 9

What are 10nm fibre chromatin made up of?

Answer 9

DNA wraps around histone proteins -this is euchromatin

Question 10

What are 30nm fibre chromatin made up of?

Answer 10

multiple histones wrap into 30nm conisisting of nucleosome arrays in their most compact form - this is heterochromatin

Question 11

Higher level DNA supercoiling of the 30nm fibre produces what?

Answer 11

The metaphase chromosome.

Question 12

What are the roles of 10nm and 30nm chromatin?

Answer 12

The chromatin can be uncoiled for the molecules of transcription/repairs etc can access the DNA and vice/versa.

Question 13

What is a nucleosome?

Answer 13

A nucleosome is made up of just under two turns of DNA wrapped around a histone octamer (a set of 4 proteins making up two discs.). The N termainal tails of the 8 core histone subunits project out and are free to interact with other proteins, facilitating regulation of chromatin structure and function.

Question 14

What feature of histone octamers means they can interact well with the phosphodiester backbone of DNA?

Answer 14

The histones are highly basic (+ve) and can interact with the
-ve DNA.

Question 15

How do histones and chromatin stay bound?

Answer 15

By electrostatic attractions.

Question 16

What is a linker histone?

Answer 16

They strap DNA onto histone octamers to limit movement of DNA relative to the histone octamer.
Acts like a clip.
Stabilising formation of 30nm fibre.
DNA rich in linker histones such as H1 is transcriptionally inactive.

Question 17

Regions of chromatin where histone octamers are depleted means what?

Answer 17

That region of DNA will be susceptible to DNA interacting proteins.

Question 18

Interphase chromatin comprises of chromatin that can reversibly condense and decondesnse without become knotted. What is this called?

Answer 18

Fractal globules

Question 19

What happens to fractal globules?

Answer 19

They can be pushed around the nucleus to areas where RNA/DNA polymerase are in high concentration for transcription. Usually heterochromatin sits on the periphery of the nucleus and moved to the centre of the nucleus when there is transciptional activation of a gene.

Question 20

Chromosomes contain specialised DNA sequences that facilitate reliable and complete DNA replication and segregation of duplicated chromosomes during cell division. What are some examples of said DNA sequences?

Answer 20

Telomeres
Replication Origins
Centromeres

Question 21

What is a telomere?

Answer 21

repeated DNA sequences at the ends of linear chromosomes that maintain chromosomal integrity
consist of TTAGGG

Question 22

What is a replication origin?

Answer 22

DNA sequence where DNA replication is initiated.

Question 23

What is a centromere?

Answer 23

DNA sequences on which kinetochore assembles and mediates chromosome segregation at mitosis and meiosis.

Question 24

What is a kinetochore?

Answer 24

Protein complex that binds microtubules on the mitotic spindle.

Question 25

What is the role of telomeres?

Answer 25

At the end of DNA replication, there is an overhang due to RNA primer. If this were left, the overhand would be digested and information would be lost. Telomerase adds repeats to preserve integrity.

Question 26

What are centromeres made up of?

Answer 26

Centromeres are alpha satellite DNA repeats for which the inner plate of the kinetochore can bind to.

Question 27

What does outer plate kinetochore bind to?

Answer 27

Kinetochore proteins bind to the microtubules of the mitotic spindle.

Question 28

Microtubules dock onto the outer plate of the kinetochore which is glued to the inner kinetochore plate. How does the inner plate of the kinetochore bind with the centromeric regions?

Answer 28

The centromeric regions contains a specific histone variant called centromeric protein - A that makes a specific series of contacts with the inner kinetochore plate.

Question 29

In yeast, how do the kinetochore like with the centromere?

Answer 29

The kinetochore is in a basket arrangements that holds a single microtubule in one end and attaches to a single nucelosome of centromeric chromatin.

Question 30

How much of the human genome encode information for making cellular proteins?

Answer 30

1.5%

Question 31

50% of the genome is made up of unique coding sequences. What do these sequence for?

Answer 31

1. Protein Coding Regions 2. Introns 3. Non-repetitive DNA that is neither introns nor codons.

Question 32

Out of the 50% of DNA that is made up of unique sequences, approximately 30/50% is made up of non repetitive DNA that is neither codons nor introns. What is it?

Answer 32

It is thought to be cis regulatory DNA that acts on genes nearby. The more protein coding genes there are, the more non coding regulatory DNA there is.

Question 33

The other 50% of the human genome is made up of repeated sequences. What are these made up of?

Answer 33

1. Simple Sequence Repeats 2. Segmental Duplications 3. Transposons

Question 34

Most of the 50% of repeated DNA in the human genome is made up of Transposons. What kinds of Transposons are there?

Answer 34

1. DNA Transposons 2. Retroviral Transposons 3. Non Retroviral PolyA Retrotransposons

Question 35

What are transposons?

Answer 35

Mobile genetic elements that jump around the genome.

Question 36

How do DNA Transposons work?

Answer 36

They move by a cut and paste mechanism without self duplication by transposase. Once cut from the strand it undergoes self repair. The cut transposome randomly inserts elsewhere into the genome.

Question 37

How do retroviral retrotransposons work?

Answer 37

Replicate via RNA intermediates producing new DNA copies that integrate at new genomic locations using self encoded reverse transcriptase.

Question 38

How do non retroviral polyA retrotransposons work?

Answer 38

Replicates via an RNA intermediate using self encoded reverse transcriptase Binds to DNA producing a second strand which is then inserted. These code from SINEs and LINEs.

Question 39

What is the purpose of transposons?

Answer 39

It is not understood, but theoretically, this helps to drive evolution.