Gene Expression - Basic Mechanisms in Transcription Flashcards
What do genes encode?
proteins
What do proteins dictate?
cell function
Do all cells have the same genetic material?
yes
What can determine cell differentiation and identity/function?
differential gene expression regulated by the combination of different transcription factors in that cell
What gene types do red blood cells have?
housekeeping and haemoglobin
What gene types do muscle cells have?
housekeeping and myosin
What gene types do pancreatic cells have?
housekeeping and insulin
What is the initiation of transcription of a gene?
the primary control point for gene expression, usually at the very beginning of the protein production process
Cells have distinct sets of transcription regulators;…
some of these regulators work to increase transcription, whereas others prevent or suppress it, such that only a fraction of the genes in a cell are expressed at any one time.
In prokaryotes, what are regulatory proteins often controlled by?
nutrient availability
Why is nutrient availability a benefit for regulatory proteins in prokaryotes?
allows organisms such as bacteria to rapidly adjust their transcription patterns in response to environmental conditions
What two steps are in gene expression to form a polypeptide?
- transcription
- translation
What does transcription produce?
RNA complementary to one strand of DNA
What does translation convert?
converts RNA sequence to amino acid sequence of a polypeptide
5 ways RNA differs from DNA
- usually one polynucleotide strand
- the sugar is ribose
- bases in RNA can pair with a single strand of DNA
- single strand RNA can fold into complex shapes by internal base pairing
- contains uracil instead of lycine
snRNA:
- small nuclear RNA
- involved in RNA processing(splicing)
miRNA:
- micro RNA
- inhibits translation
tRNA:
- transfer RNA
- adapter between amino acids and mRNA sequence
mRNA:
- messenger RNA
- protein-coding sequence of a gene
rRNA:
- ribosomal RNA
- structural and catalytic component of the ribosome
Which way is RNA synthesised?
5’ –> 3’
Formation of the linkage between nucleotides always occurs by adding what to what?
the 5’-phosphate end of the new nucleotide to the 3’-OH end of the nucleic acid
3 transcription components
- nucleoside triphosphates as substrates
- an RNA polymerase enzyme
- a DNA template for base pairings
Parts of a gene:
- promoter
- transcription initiation site
- RNA coding sequence
- terminator
- transcription termination site
What does RNA polymerize?
synthesis of RNA, complementary to a DNA template strand
RNA polymerases are processive:…
a single enzyme-template binding results in polymerization of hundreds of RNA bases
Do RNA polymerases need primers?
no
Do RNA polymerases need to proofread?
no
3 steps of transcription:
- initiation
- elongation
- termination
Initiation: Sigma factors and transcription factors are proteins that do what?
they bind to the promoter DNA sequences, recruit DNA polymerase to the promoter, and help determine which gens are expressed at particular times
Initiation: What do promoters do?
direct the enzyme where to start and which strand of DNA to transcribe
At which stage of transcription does unwinding of DNA occur?
initiation
What is the initiation site?
where transcription begins (promoters have these)
Elongation: How many base pairs at a time does RNA polymerase unwind DNA?
about 10 base pairs at a time
Elongation: Which direction is DNA unwound?
3’ –> 5’
Elongation: Is the transcript parallel or antiparallel to the DNA template strand?
antiparallel
Elongation: Do RNA polymerases proofread and/or correct mistakes?
no and no
Elongation: What do RNA polymerases use as substrates?
nucleoside triphosphates(NTPs)
Elongation: How many phosphate groups are removed from each substrate molecule?
two
What is termination specified by?
a specific DNA sequence
Termination: What two things may happen?
- the transcript forms a loop and falls away from the DNA
- a protein binds to the transcript and causes it to detach from the DNA
