4.92.2 Mb Eukaryotic Genetics 2 - The Maumus Shitstorm Continues

Front 1

Define contour length

Back 1

The maximum possible length of the DNA helix assuming a B-form conformation

Front 2

All Eukaryotes have at least __ chromosomes

Back 2

2

Front 3

The variability in chromosome number is related to genome size and organism's biological features. True or false?

Back 3

False, number of chromosomes is not related to genome size, nor complexity of the organism phenotype. For example, salamanders have genome 30× than human but half the chromosomes

Front 4

Why bother with chromosomes? Why even bother with this lecturer and his blatant plagiarism / lack of effort?

Back 4

Because without chromosomes, DNA would not be able to fit inside the nucleus and remain ordered without getting tangled. Replication is impossible if there are no chromosomes

Front 5

What is the purpose of histones?

Back 5

DNA is wrapped around histones to be compacted

Protects chromatin from endonucleases

Post translational modifications to residues on the histones increases or decreases accessibility of DNA to transcription machinery and therefore gene expression

Front 6

1 nucleosome = an _______ of histones,

how are they arranged?

Back 6

Octamer, stacked on top of each other to make compact coil

Front 7

Draw the structure of 1 nucleosome

Back 7

H1 linker histone

Front 8

Draw the arrangement of 6 nucleosomes

Back 8

Front 9

What is a lampbrush chromosome?

Back 9

Selenoid coiled around protein core made up of histone H1 and other proteins

Front 10

Describe the different forms of chromatin

Back 10

Euchromatin (Open, Transcriptionally Active)

Heterochromatin (Condensed, Less Active)

- ’Facultative’ (can be changed to euchromatin)

- ‘Constitutive’ (condensed throughout cell cycle

Front 11

Where is euchromatin more commonly found in the chromosome?

Back 11

Front 12

What is the function of telomeres? What are they made of?

Back 12

-enable the cells’ machinery to distinguish between “real” ends from double stranded break.

- made up of a repeated motif (5’-TTAGGG-3’ in most eukaryotes).

Front 13

Describe the steps of RNA processing (4)

Back 13

1. Transcription, capping of 5' end

2. Cleavage

3. Polyadenylation of 3' end

4. Splicing

Front 14

Describe the process of RNA capping

Back 14

1. Guanylyl transferase - removes diphosphate from GTP and α phosphate from the guanosine monophosphate

2. Guanine methyltransferase adds methyl group to N7 with SAdenoMet.

3. Methylguanosine, 5' phosphate and PPi joined together

Front 15

What is the purpose of polyadenylation? (2)

Back 15

mRNA stability and recognition of transcription finish line, not just DSBs

polyA forms complex with PolyA binding protein (PABP) and prevents degredation

Front 16

Describe the process of polyadenylation (3)

Back 16

1. AAUAAA followed by CA 10-30 bp downstream followed by another GU rich sequence are recognition sites for Cleavage and polyadenylation specificity factor (CPSF) and Cleavage stimulation factor (CstF)

2. CstF recruited by CPSF and cleaves off GU rich region

3. Poly-A polymerase adds 250 A nucleotides, using ATP

Front 17

What is the consensus sequence for an intron? (5)

Back 17

AG at the end of exon

GU at the start of intron

A branch point in the middle of intron (NOT SHOWN)

AG at end of intron

G at the start of the next exon

Front 18

Describe the chemical process of splicing

Back 18

1. Formation of Lariat intron - 2'OH on A performs nucleophilic attack on phosphate at the end of upstream exon to form Intron loop attached to upstream exon, and looped together by phosphoester bond between phosphate and 2' OH. OH group on exon end now exposed.

2. Exposed OH at the end of the exon does an nucleophilic attack on phosphate at the beginning of downstream exon, which then kicks off the lariat intron

Front 19

Describe the topological process of splicing (4)

Back 19

1. Spliceosomes carry out splicing, made of small nuclear snRNAs, proteins and mRNAs to make up the small ribonucleoprotein, which form the complex.

2. U1 binds to upstream GU, and U2 binds to A at branch point U4&6 + U5 displace U1 and form complex with U2

3. U4 & 6 cleaves with upstream exon from the UG point

4. Ligation onto the beginning of downstream exon by U5

Front 20

Define alternative splicing

Back 20

When different proteins can be made by the splicing out of particular exons

Front 21

Give an example of alternative splice mutants

Back 21

Dscam, neural adhesion molecule in Drosophila, has 24 exons, and 4 of them can be spliced out

Front 22

Define group 1 introns

Back 22

Found in pre-rRNA, mRNA and tRNA and is autocatalytically spliced out

Induced by free GTP binding to active site formed by the intron sequence itself

Front 23

Define group 2 introns

Back 23

Found in organelle genomes, can also selp splice, but act differently, using the adenine on the sequence itself.