Unit 3:Transcription and Translation and Unit 4 Flashcards
In translation how many stands are being transcribed?
one-called the template strand-3’ to 5’
What does mRNA code for?
protein
what is rRNA’s function?
form the core of the ribosome and catalyze protein synthesis
what is miRNA’s function?
regulate gene expression
what is tRNA’s function?
serves as adaptors between mRNA and amino acids during protein synthesis
what the other small RNA’s function?
used in RNA splicing, telomere maintenance, and many other processes
What is holoenzyme?
made up of core enzyme, which has ability to synthesize RNA and regulatory subunit (sigma factor)
Where are promoters in prokaryotic Dna.
promoters have two key regions:
-10 box – 10 bases upstream from start site
-35 box – 35 bases upstream
(transcription starts at +1)
typical sequences found at boxes, rest of promoter highly variable
transcription begins when sigma identifies and binds to –10 and –35 boxes, properly orienting the RNA polymerase holoenzyme for transcription at start site
What genes does RNA polymerase 1 transcribe?
most rRNA genes
What genes does RNA polymerase 2 transcribe?
protein-coding genes, miRNA genes, plus genes for some small RNAs
What genes does RNA polymerase 3 transcribe?
-tRNA genes
-55 rRNA gene
-genes for many other small RNAs
Ignition of Transcription in Eukaryotes
TATA box recognized by TBP (TATA binding protein), a subunit of TFIID
binding of TFIID distorts helix, allows other factors (TFIIA, B, C, etc) to pile on to form ‘transcription initiation complex’
TFIIH pries apart double helix at transcription start point …
Who is Francis Crick?
Francis Crick proposed that an ‘adapter molecule’ held amino acids in place while interacting directly and specifically with a codon in mRNA.
What is the wobble hypothesis?
wobble hypothesis: the anticodon of tRNAs can still bind successfully to a codon whose third position requires a nonstandard base pairing
What are the functions of the membranes?
-provide a selectively permeable barrier
-prevent unrestricted exchange of molecules
-transport solutes
-exchange of molecules across the membrane
-respond to external signals - signal transduction
-signals travelling from a distance or from nearby cells
-energy transduction - conversion of one form of energy into another
-compartmentalization (eukaryotes)
-create separate environments for different activities
-scaffold for biochemical activities
What is the movement of phospholipids within the membrane?
phospholipids are constantly moving
spinning in place; travelling laterally within ‘leaflet’
phospholipids are occasionally ‘flipped’ to the opposite leaflet during membrane synthesis but they rarely ‘flop’ back
What effects fluidity of membranes?
-temperature
-changes in lipid composition that affect alignment of phospholipid tails
-tightly packed tails =>membrane more viscous, less fluid
-freely moving tails => higher fluidity
What happens with changes of transition temperature?
-temperature at which a membrane transitions between the fluid phase and gel phase
-above Tm =>membrane ‘melts’ => lipids more freely, rotationally, laterally within leaflets
-below Tm =>hydrophobic tails pack together =>
membrane gels => incompatible with life
What affects transition temperature?
Tm (fluid/gel transition temp) affected by:
1.altering length of fatty acid chains
-longer chains =>
more interactions between fatty acid tails => tighter packing =>
less fluid at a given temp
higher Tm, higher temp to ‘melt’
-range 14-24 carbons in membrane fatty acids
- altering degree of saturation of fatty acids => # double bonds
-more double bonds => less packing =>
more fluid at a given temp
lower Tm, lower temp to ‘melt’
-membrane phospholipids typically have one saturated fatty acid and one with one or more double bonds
Tm (fluid/gel transition temp) in eukaryotic cells also affected by: - altering amount of sterol (eg cholesterol)
-especially animal cells - can be up to 50% of membrane lipid
-cholesterol acts as a ‘buffer’, inhibiting phase transitions when temp changes
-higher cholesterol at cool temps => membrane more fluid
-higher cholesterol at warm temps => membrane less fluid
-cholesterol effects similar to antifreeze/coolant in car engine!
-lowers the freezing point of engine fluid to prevent freezing in winter
-raises the boiling point in summer to prevent overheating
What is A (aminoacyl or acceptor) site?
