GENO- structure and function of the human genome

Question 1

describe the structure of DNA

Answer 1

double stranded - sugar phosphate backbone - deoxyribose sugar
ACGT- A,G- purines, C,T - pyrimidine
2 bonds between A,T
3 bonds between C,G

Question 2

describe the structure of chromosomes

Answer 2

sister chromatids, teleomere at each end, centromere in the middle,
P arm = short arm
q arm = long arm

Question 3

describe the 4 types of chromosome

Answer 3

metacentric - centromere in the centre of the chromosome
sub-metacentric - centromere just off the centre
acrocentric - centromere near the tip
telocentric - centromere joins both at one end - humans dont have these

Question 4

what three key features identify chromosomes

Answer 4

size, banding pattern, centromere position

Question 5

what is the banding pattern of DNA due to

Answer 5

chromosome structure
chromosomes exist as chromatin 
DNA double helix binds to histones
octamer of histones forms a nucleosome 
nucleosomes stack to form a solenoid

banding is due to the fact to euchromatin stains different to heterochromatin

Question 6

what is the difference between euchromatin and heterochromatin

Answer 6

euchromatin - extend state, dispersed through the nucleus
allows gene expression

heterochromatin - highly condense, genes not expressed

Question 7

what is the function of centromeres

Answer 7

keeps sister chromatins together
attach to microtubules during cell division
rich in heterochromatin
normally highly repetitive

Question 8

what are the functions of telomers

Answer 8

protect the ends of the chromosome
telomerase repair telomeres but is only active in certain types of cells
it is switches on in the wrong cells this can lead to cancer

Question 9

what are the functional units of a gene

Answer 9

cistron

Question 10

what is the human genome including the mitochondrial genome

Answer 10

DNA
22 pains of autosomes
1 pair of sex chromosomes
transcribed units = genes - protein coding, RNA only coding

mitochondria genome:
13 coding genes
24 non-coding genes
only ova provide mitochondria so this is maternal inheritance

Question 11

define exome

Answer 11

part of the genome that codes for proteins
exon - codes for amino acids
UTR- contains regulatory elements
introns- non-coding region between exons
promotor region - 5’ end of gene that contains important regulatory elements for transcription

Question 12

what is meant by epigenome

Answer 12

methyl and histone groups

chemical compounds that attach to DNA or histone and can affect gene activity

Question 13

how do methyl / histone groups affect gene activity

Answer 13

alters chromatin structure. recruit histone modifiers . repress transcription / genome-wide pattern established at fertilisation / important for differential gene expression (transcription), response to environmental cues

Question 14

outline an understanding of what is meant by differential gene expression

Answer 14

methyl / histone groups = control gene expression

temporal - in time - development, response to hormones, infections etc.

spatially - different tissues / cells express different genes (e.g., liver vs brain)

Question 15

what happens when there is a failure to regulate gene expression

Answer 15

metabolic diseases, metastasis, congential disorders, cancer