The Eukaryotic Genome Flashcards
Why is the amount of proteins that can be encoded for in the human genome not close to the expected number, but is for E.coli?
The human genome is more complex and contains a lot of non-coding DNA/RNA.
How many protein coding sequences are in the human genome? What percentage is this of the genome?
30,000. 2%.
What does the human genome consist of?
Regulatory sequences, introns (non-coding RNA that is transcribed but not translated). pseudo genes, non-coding RNA (infrastructural RNA, regulatory RNA), repetitive DNA.
How does non-coding parts of the genome relate to the evolutionary chain?
As we more up the chain we see more non-coding DNA in the genome.
What is the rate of renaturation proportionate to?
Number of times the sequence is present in the genome.
What is a repetitive sequence?
Sequences like telomeres which repeat but don’t have enough information to encode for proteins.
What is the relation to the complexity of DNA and it’s ability to re-anneal.
Hyperchromic effect and Tm. Simple DNA re-anneals quickly and easily, complex take much longer as all sequences are unique.
What are the four classes of eukaryotic genomic DNA?
highly repetitive
moderately repetitive
slightly repetitive
single copy sequences
Explain highly repetitive DNA.
Short sequences arranged in repeats - AGCAGCAGC etc…often found clustered around the centromere or telomere.
Explain moderately repetitive DNA.
Segments of 100 to several thousand base pairs repeated - groups of genes whose products are needed by cells in large quantities e.g histones, ribosomal and tRNA.
Explain slightly repetitive DNA
Most genes in the genome are only represented once. E.g globin family - sometimes clustered together on one chromosome.
Explain single copy genes in DNA.
Most of the genes of the organism are single copy genes. Take the longest time to re-anneal and are the ones encoding for proteins.
Which genes encode for proteins?
Single copy genes.
Why is compaction necessary for genetic information to fit into the nucleus?
Human cell has 3 billion bp of DNA with each having a thickness of 3.4 A - total length of DNA 2m, size of nucleus 10-15 micro metres.
What is responsible for packaging genetic information in human cells?
Chromosomes.
What are the features of a chromosome?
Physical card 17
What is chromosome banding?
Chromosomes can be stained with dyes which give a unique pattern for each chromosome so that the bands can be numbered.
What is the most common stain used for chromosome banding and how is it used?
Giemsa stain. When applied after mild proteolytic treatment gives a light and dark band pattern.
What is chromatin?
The genetic material which makes up the chromosomes - composed of DNA and protein.
What is heterochromatin?
Tightly packaged - isn’t transcribing much.
What is euchromatin?
Euchromatin contains most active genes; actively transcribed.
How much DNA does each chromosome contain?
A single molecule of DNA.
DNA is wound around ______ called ______.
Small proteins. Histones.
Histone proteins have a ____ charge. This allows for association with the ______.
Positive. Negatively charged backbone.
What is a histone octamer? How is it formed? What is the resulting structure?
Physical card 37
What is the major force holding the association of histones to DNA?
Electrostatic.
How can DNA and histones be separated?
Take advantage of electrostatic bond. Chromatin treated with high ionic strength solutions to reduce electrostatic interactions and protein dissociates from the DNA.
What is the role of histones?
Shield negative charges of phosphates.
Allow bending and DNA wrapping.
Restrict access to transcription.
What is histone remodelling?
Influences DNA accessibility for transcription.
What are the ways in which histones can be modified?
Phosphorylation
Methylation
Acetylation
What is Acetylation?
Transferring an acetyl group to the amino acid chain of lysine residues.
What do histone acetyl transferases do?
Histone acetyl transferases (HATs) add acetyl groups, neutralise the lysine positive charge and weaken the electrostatic interactions between phosphates from DNA and histones - loosen the packaging - allows for increased gene expression.
What do histone deacetylases (HDACs) do?
Remove acetyl groups, enhance electrostatic interactions and tighten packaging.
What is the mechanism by which HATs perform?
Associated with transcriptional co-activators - relaxes chromatin and provides binding sites for proteins that stimulate transcription.
