MolBio4 - 32

Question 1

What does the word chromosome actually mean?

Answer 1

Coloured body

Question 2

Where is most eukaryotic DNA stored?

Answer 2

Chromosomes

Question 3

Other than linear DNA, what does each chromosome also comprise?

Answer 3

Proteins: packaging and folding; controlling replication, repair and recombination; mainting integrity; regulating gene expression

Question 4

During what phase of mitosis are chromosomes easily distinguished?

Answer 4

Metaphase

Question 5

What is the term given to the organised represenation of all the chromosomes at metaphase?

Answer 5

Karyotype

Question 6

What is the karyotype of an organism?

Answer 6

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

Question 7

Describe chromosome arrangement during interphase

Answer 7

Each occupies a distinct subdomain of the nucleus, and transcriptionally inactive DNA is in the periphery

Question 8

Describe chromosome movement during transcription

Answer 8

Activation is accompanied by movement from the periphery to the centre, indicative of very high order controls

Question 9

Describe the general structure of chromatin

Answer 9

Highly coiled - looks like beads on a string - beads are nucleosomes

Question 10

What are nucleosomes?

Answer 10

Protein core around which DNA coils like cotton on a bobbin

Question 11

What are the protein subunits of nucleosomes called?

Answer 11

Core histones

Question 12

How many subunits form a nucleosome?

Answer 12

8

Question 13

What is special about nucleosome subunits?

Answer 13

Tails that are free to interact with other proteins

Question 14

What are linker histones?

Answer 14

Proteins that strap DNA onto the core histone octamers and limit movement of DNA relative to the nucleosome

Question 15

What packaging effet do histone octamers induce?

Answer 15

DNA packaged into compact, flexible 30nm chromatin scaffold that can be remodelled to accommodate protein complexes for gene transcription/replication

Question 16

What are the two specialised DNA sequences imperative for DNA function?

Answer 16

Telomeres and centromeres

Question 17

What are telomeres?

Answer 17

Specialist overhanding single stranded TTAGGG repeats at ends of chromosomes, protecting the length of the chromosome, that can be several hundred nucleotides long

Question 18

What are centromeres?

Answer 18

Location of attachment of the mitotic spindle during cell division, ensuring faithful segregation of sister chromatids

Question 19

Outline the structure of a centromere

Answer 19

Made up of tandem repeats of alpha-satellite DNA that convey affinity for the kinetochore inner plate proteins. Kineotchore outer plate proteins bind to the inner plate, and then the protein components of the mitotic spindle

Question 20

What is CENP-A?

Answer 20

Gene that encodes the specialist H3 histone that mediates the attachment of chromsome to kineotchore

Question 21

What percentage of DNA sequence encodes cellular proteins?

Answer 21

1.50%

Question 22

What percentage of the human genome is made up of repeated DNA?

Answer 22

50%

Question 23

What is 50% of human DNA?

Answer 23

Repeated copies of retrotransposons known as parasitic DNA

Question 24

What are transposons?

Answer 24

Mobile genetic elements that jump around the genome

Question 25

What are the three types of transposons?

Answer 25

DNA, retroviral and non-retroviral polyA

Question 26

Why are DNA transposons important?

Answer 26

They confer the ability to mass re-arrange DNA

Question 27

How do DNA transposons work?

Answer 27

Mover around by 'cut-and-paste' WITHOUT self-duplication

Question 28

How do retro-viral transposons work?

Answer 28

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

Question 29

Outline the process of retro-viral replication.

Answer 29

Entry into cell > loss of envelope > single RNA > RNA/DNA > DNA double helix > integration > transcription > translation > more virus to infect organism

Question 30

Where are polyA retrotransposons commonly found?

Answer 30

Verterbrate genomes

Question 31

How do polyA retrotransposons replicate?

Answer 31

Via RNA intermediate using retro-transposon-encoded reverse transcriptase

Question 32

Outline the polyA retrotransposon replication mechanism

Answer 32

Element transcribed and translated to produce reverse transcriptase which then binds back onto the element. This then cleaves the first strand of target DNA, and reverse transcribes the RNA into the genome. Multistep process produces second DNA strand with element copy at new position