Lecture 2 - Organisation of Genetic Information

Question 1

DNA supercoiling

Answer 1

Compacts DNA packaging

Positive - same way as DNA helix
Negative - opposite way

DNA is usually negatively supercoiled in cells which favour unwinding

Local unwinding is necessary for DNA replication, transcription and recombination

Question 2

DNA packaging

Answer 2

Double helix with paired nucleotides stack on top of each other

Question 3

Chromatin

Answer 3

consist of tightly packed, coiled nucleosomes

Question 4

Nucleosomes

Answer 4

contain DNA wrapped around histone proteins

Eukaryotic supercoiled DNA is stabilised by nucleosomes

Question 5

Euchromatin vs Heterochromatin

Answer 5

Euchromatin is least condensed region of chromatin. Rich in genes

Heterochromatin is the most condensed regions. contain non-coding DNA and very few genes

Question 6

Plasmids

Answer 6

in prokaryotes

genes on plasmids can encode proteins that are beneficial to the cell for example, provide antibiotic resistance or aid growth

Question 7

Organisation in Eukaryotes

Answer 7

individual genes in eukaryotes generally have their own promoter

each gene contains exons (coding) and introns (non-coding)

introns allow for alternative splicing of mRNA resulting in different protein sequences and structures

Question 8

Chromosomes in Prokaryotes

Answer 8

most chromosomes are circular

prokaryotes do not have membrane bound nucleus

proteins involved in DNA replication and recombination, transcription and translation remain closely associated with the prokaryotic chromosome

the region of DNA and is associated proteins in called the nucleoid

Question 9

Chromosomes in Eukaryotes

Answer 9

chromosomes are linear

usually present in pairs, or homologues

eukaryotes have two copies of each gene, alleles, one copy on each homologous chromosome

alleys are located in the same specific place, or locus on homologous chromosomes

chromosomes are visible in prophase due to further condensation of the chromatin

in interphase chromosomes are less tightly packed

in interphase each chromosome is arranged in a defined area of the nucleus, called chromosome territory

Question 10

Genome

Answer 10

The complete set of genetic material in a cell or organism

Question 11

Genome size in Eukaryotes and Prokaryotes

Answer 11

Eukaryotes genomes are large but, in mammals, only around 1% of their genomes encode proteins

Prokaryote genomes are small and genes are situated very close to each other. Most encode proteins

Question 12

Organisation of human genome

Answer 12

~21,000 functional genes in human genome

98% is non-coding DNA

45% is comprised of repetitive sequences from transposable elements

19,000 pseudogenes (non-functional genes)