Lecture 13

Question 1

Eukaryotes:

Answer 1

• very varied, include fungi, insects, alga, protozoan, flowers, animals
• multicellular, different sets of expressed genes depending on the cell type

Question 2

Prokaryotic cell:

Answer 2

• Cell membrane, cell wall, flagellum, ribosomes, DNA in a nucleoide structure
• Genes expressed according to the signals recieved

Question 3

Eukaryotic cell:

Answer 3

• Larger size than prokaryotic cell
• Their DNA is located in a nuclear envelope within a Nucleus. They have a lot more DNA.
• A nucleolus is where the ribosomes are created
• Gene regulation is easy due to selection of transcription factors and entry to the nucleus

Question 4

Chromosomes in the nucleus of eukaryotic cells:

Answer 4

• Metaphase chromosomes are highly structured, as genes aren’t being transcribed
• Interphase chromosomes are slightly less structured

Question 5

DNA packaging in eukaryotes:

Answer 5

• Chromatin packages DNA into histone proteins (DNA double helix, chromatin, nucleosomes, condensed section of chromatin)
• This is dynamic as DNA moves in response to the cell cycles and in response to what genes are being turned on and off in the nucleus.

Question 6

Nuclear localisation:

Answer 6

• A region of non-transcribed genes is found around the outside of the nucleus. Genes found here are usually silenced
• Genes that are transcribed are at the centre of the nucleus.
• This happens in response to signals from the external environment

Question 7

Factors influencing genome size:

Answer 7

• Gene density (intergenic regions)
• Introns (size and number)
• Repeats
• Gene size between eu- and pro- karyotes are pretty similar, but the genome size varies due to each gene having their own regulating sequences.

Question 8

Eukaryotic RNA polymerases:

Answer 8

• 3 DNA dependent RNA polymerases
• ## beta and beta’, alpha, and additional enzyme specific subunits.

Question 9

RNAPI:

Answer 9

• Ribosomal RNAs
• 5.8s
• 18s
• 28srRNA genes

Question 10

RNAPII:

Answer 10

• all protein coding genes, plus snoRNA genes, miRNA genes, siRNA enes, and most snRNA genes

Question 11

RNAPIII:

Answer 11

• tRNA genes, 5S rRNA gnes, some snRNA genes and genes for other small RNAs

Question 12

Eukaryotic RNAs:

Answer 12

• Lots of types!

Question 13

mRNA:

Answer 13

• messenger RNA

- code for proteins

Question 14

rRNA:

Answer 14

• Ribosomal RNA

- Form the basic structure of the ribosome and catalyse protein synthesis

Question 15

tRNA:

Answer 15

• Transfer RNAs

- Central to protein synthesis as adaptors between mRNA and amino acids

Question 16

snRNAs:

Answer 16

• Small nuclear RNAs

- Function in a variety of nuclear processes, including the splicing of pre-mRNA

Question 17

snoRNAs:

Answer 17

• Small nucloelar RNAs

- Used to process and chemically modify rRNAs

Question 18

scaRNAs:

Answer 18

• Small cajal RNAs

- Used to modify snoRNAs and snRNAs

Question 19

miRNAs:

Answer 19

Micro RNAs

- Regulate gene expression typically by blocking translation of selective mRNAs

Question 20

siRNAs:

Answer 20

• Small interfering RNAs
• Turn off gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures

Question 21

3’ modifications:

Answer 21

• Run of Adenines As
• Important for stability and regulation of translation
• Ribosomal endonucleases can’t degrade it

Question 22

5’ cap:

Answer 22

• Protects from degradation

- Involved in when the RNA is expressed/translated

Question 23

Gene organisation in the Drosophila Adh region:

Answer 23

• osp (outspread wings) mutations mapped to both sides of the Adh genes, as it is within an intron of the Adh gene
• Adh, Adhr, two other genes within introns of osp!
• Multiple start sites, multiple poly(A) sites and different splicing

Question 24

Initiation of transcription:

Answer 24

• RNAPII is involved in protein coding genes
• Steps in transcription at Class II (RNAPII) promoters:
  1. Formation of the pre-initiation complex
  2. Separation of the 2 DNA strands
  3. Initiation
  4. Promoter clearance
  5. Elongation
  6. Termination

Question 25

Transcription complexes involve these things:

Answer 25

- Transcription initiation (RNAP starts) - Transcription termination (RNAP falls off) - 5-methyl guanine cap - PolyA tail at 5' end

Question 26

A TATA box is:

Answer 26

- A consensus sequence found in genes that codes for the promoter - The RNAP recognises the TATA box - A sigma factor or GTF recognises the promoter allowing RNAP to bind and transcribe

Question 27

Transcription Factor TFIID:

Answer 27

- TATA binding protein - TBP associated factors - Binds core promoter elements and initiates assembly of the pre-initiation complex on the promoter - Different TFs recognise different sequences so different genes are transcribed by RNAP

Question 28

Phosphorylation steps on the 3' tail after transcription:

Answer 28

- Determine capping, intron splicing, polyadenylation and intron splicing - Important for what happens next for that particular transcript