chromosome structure

Question 1

Diploid eukaryotic cells contain ….

Answer 1

• Diploid eukaryotic cells contain two copies of each chromosome
• Each chromosome pair differs in size and DNA sequence content

Question 2

what is the karyotype

Answer 2

• The organized representation of all the chromosomes in a eukaryotic cell at metaphase (B) is called the karyotype of the parent organism

Question 3

what is the 30nm fibre

Answer 3

• The “30nm” fibre is a supercoiled version Structure: a supercoiled array of nucleosomes
• Biochemical analysis of nucleosomes reveals a protein core around which DNA is wound, like cotton on a bobbin

Question 4

what is histone

Answer 4

• DNA is packaged by histone octamers into a compact, flexible 30nm chromatin scaffold that can be remodelled to accommodate protein complexes involved in gene transcription and DNA replication – if the appropriate proteins are recruited
• Chromatin is engineered to permit flexible responses to altered transcription factor activity caused by changes in cell differentiation status and changes in signalling pathway activities

Question 5

what occurs at the n terminus of histones

Answer 5

• The N-terminal tails of the 8 core histone subunits project out from the nucleosome core and are free to interact with other proteins, facilitating regulation of chromatin structure and function

Question 6

what do linker histones do

Answer 6

• Linker histones such as H1 strap DNA onto histone octamers and limit movement of DNA relative to the histone octamer - stabilizes formation of 30nm fiber and facilitates the establishment of transcriptionally silent heterochromatin

Question 7

in interphase what form does chromatin exist in

Answer 7

• Interphase chromatin comprises a set of dynamic, “fractal globules” that can reversibly condense and decondense without becoming knotted
• The nuclear periphery in interphase cells is is composed of transcriptionally inactive DNA (red)
• RNA transcripts (green) are excluded from the periphery
• Transcriptional activation of a gene is accompanied by movement from the periphery towards the centre of the nucleus

Question 8

What ar telomeres

Answer 8

• specialized DNA sequences at chromosome ends
• Single-stranded 3’ overhanging TTAGGG repeat arrays
• synthesised by the Telomerase enzyme and can be several hundred nucleotides long.
• Telomeres are replicated by a specialised DNA Polymerase called Telomerase.
• Telomeres define chromosome ends and maintain chromosome integrity

Question 9

What are centromeres

Answer 9

• Chromosome segregation during cell division requires attachment of chromosomes to the mitotic / meiotic spindle.
• Centromeres contain specialized proteins and DNA sequences that facilitate chromosome segregation during cell division

Question 10

three types of non coding DNA

Answer 10

• Almost half of the human genome sequence is made up of 3 different types of repeated DNA sequences called Transposons

1. DNA Transposons
2. Retroviral retrotransposons
3. Non-retroviral polyA retrotransposons