Lecture 8: Genes Flashcards
1
Q
genes
- definition
- function
- contains (2)
A
- basic physical and functional unit of heredity
- code for molecules that have a function (proteins or DNA)
- contains regulatory and other non-coding sequence
2
Q
What is the central dogma?
A
- genes flow from DNA to RNA to protein
3
Q
genetic code:
- coding strand
- template strand
- RNA strand
- amino terminus
A
- coding: 5’ –> 3’ (ATG)
- template strand: 3’3’
- expressed amino acids
4
Q
Where does gene expression (transcription and translation) occur in prokaryotes and eukaryotes?
A
- prokaryotes: cytoplasm
- eukaryotes: transcription in nucleus and translation in cytosol
5
Q
Transcription
- describe and what enzyme is involed?
- role of that enzyme
- what binds RNA to DNA
A
- DNA template–> RNA synthesis through RNA polymerase
- RNA polymerase: forms phosphodiester bond to 3’ OH
- H bonds bind RNA to DNA
6
Q
Describe transcription as it occurs in prokaryotes
A
- sigma binds to the promotor and RNA polymerase opens up the DNA helix, sigma is released after transcription begins and RNA synthesis continues (elongation)
- termination signal codes for RNA that forms hairpin, RNA polymerase releases RNA, transcription is terminated
7
Q
define:
- sigma (what is it? what does it bind to?)
- holoenzyme
A
- sigma: cofactor of RNA polymerase; binds to promotor (segment of DNA)
- holoenzyme: complex enzyme + cofactor combined
8
Q
How does transcription differ in eukaryotes vs bacteria?
- RNA polymerase
- promotor structure
- proteins associated with promotor
- termination signal
A
- RNA polymerase: 3 types vs 1
- promotor structure: more variable and usually includes TATA box; bacteria: usually a -35 box and a -10 box
- proteins asssociated with promotor: many vs sigma
- termination signal: mRNA AAUAA vs hairpin
9
Q
How is RNA processed in eukaryotes?
A
- introns are removed by splicing
- a 5’ cap and 3’ poly A tail is added (cap protects against degradation and binds to ribosome; tail houses termination signal)
- mRNA is now processed and released into cytosol
10
Q
How is translation in prokaryotes different from eukaryotes (3)?
A
- occurs while transcription is ongoing
- occurs at start codon
- first aa-tRNA is modified methionine
11
Q
aminoacyl tRNA
A
- tRNA bonded to amino acid by 3’ of acid
12
Q
Translation (eukaryotes)
A
- ribosome small subunit binds to cap and scans mRNA for start codon; initiator aminoacyl tRNA binds to P site
- first aa-tRNA is methionine
- new tRNA joins at A site and amino acids form a peptide bond
- translocation: new trNA joins, old TRNA exits at E site, everything shifts down 1
- termination: release factor binds to stop codon, polypeptide and tRNAs leave , ribosome subunits separate
13
Q
explain each site from translation
A
- P site: houses growing polypeptide attached to tRNA
- E site: holds tRNA that will exit
- A site: holds aa-tRNA
14
Q
explain the difference between a negative and positive gene expression control
A
- negative: repressor proteins inhibit genes and stop transcription (especially when too strongly expressed)
- positive: activator protein stimulates expression especially when gene is weakly expressed (most eukaryotic genes need positive controls)
15
Q
why do chromosomes need to be unpacked
A
- inaccessible genes cannot be expressed and must be partial unpacked
- histones act as spools for DNA to wind around to make compact and turn into nucleosomes
