Lecture 13 Flashcards
Eukaryotes:
- very varied, include fungi, insects, alga, protozoan, flowers, animals
- multicellular, different sets of expressed genes depending on the cell type
Prokaryotic cell:
- Cell membrane, cell wall, flagellum, ribosomes, DNA in a nucleoide structure
- Genes expressed according to the signals recieved
Eukaryotic cell:
- 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
Chromosomes in the nucleus of eukaryotic cells:
- Metaphase chromosomes are highly structured, as genes aren’t being transcribed
- Interphase chromosomes are slightly less structured
DNA packaging in eukaryotes:
- 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.
Nuclear localisation:
- 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
Factors influencing genome size:
- 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.
Eukaryotic RNA polymerases:
- 3 DNA dependent RNA polymerases
- ## beta and beta’, alpha, and additional enzyme specific subunits.
RNAPI:
- Ribosomal RNAs
- 5.8s
- 18s
- 28srRNA genes
RNAPII:
- all protein coding genes, plus snoRNA genes, miRNA genes, siRNA enes, and most snRNA genes
RNAPIII:
- tRNA genes, 5S rRNA gnes, some snRNA genes and genes for other small RNAs
Eukaryotic RNAs:
- Lots of types!
mRNA:
- messenger RNA
- code for proteins
rRNA:
- Ribosomal RNA
- Form the basic structure of the ribosome and catalyse protein synthesis
tRNA:
- Transfer RNAs
- Central to protein synthesis as adaptors between mRNA and amino acids
snRNAs:
- Small nuclear RNAs
- Function in a variety of nuclear processes, including the splicing of pre-mRNA
snoRNAs:
- Small nucloelar RNAs
- Used to process and chemically modify rRNAs
scaRNAs:
- Small cajal RNAs
- Used to modify snoRNAs and snRNAs
miRNAs:
Micro RNAs
- Regulate gene expression typically by blocking translation of selective mRNAs
siRNAs:
- Small interfering RNAs
- Turn off gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures
3’ modifications:
- Run of Adenines As
- Important for stability and regulation of translation
- Ribosomal endonucleases can’t degrade it
5’ cap:
- Protects from degradation
- Involved in when the RNA is expressed/translated
Gene organisation in the Drosophila Adh region:
- 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
Initiation of transcription:
- 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
Transcription complexes involve these things:
- Transcription initiation (RNAP starts)
- Transcription termination (RNAP falls off)
- 5-methyl guanine cap
- PolyA tail at 5’ end
A TATA box is:
- 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
Transcription Factor TFIID:
- 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
Phosphorylation steps on the 3’ tail after transcription:
- Determine capping, intron splicing, polyadenylation and intron splicing
- Important for what happens next for that particular transcript
