L12b- Transcription and translation Flashcards
Where do the following take place?
a) Transcription
b) Translation
a) in the nucleus
b) in the cytoplasm
Transcription:
a) What is it?
b) What is the enzyme?
c) What are the 3 stages?
a) Transcription is the process by which DNA is copied (transcribed) to RNA, which carries the information needed for protein synthesis
b) RNA polymerase
c) initiation, elongation and termination
A) What does RNA polymerase do?
B) What direction does it work in?
A) - the main enzyme involved in transcription
- uses single stranded DNA template to synthesise a complementary stand of RNA
B) - builds an RNA strand in the 5’ to 3’ direction (adding a new nucleotide to the 3’ end) = reads in 3-5 direction
Stages of transcription?
- Initiation: Transcription factor binds to promotor, sequence which signal RNA polymerase to come in
RNA polymerase binds to a sequence of DNA called the promoter found near the beginning
- one bound, RNA polymerase separates the DNA strands providing the single stranded template needed for transcription - Elongation:
- One strand of DNA acts as a template for RNA polymerase: template strand
- RNA polymerase reads one base at a time and builds up an rna molecule out of complementary nucleotides making a chain that grows from 5’ to 3’ end
- RNA transcript contains same info as non-template (coding) strand of DNA but contains base uracil (U) instead of thymine (T) - Termination:
- sequences called terminators signal that RNA transcript is complete
- once they are transcribed they cause transcript to be released from RNA polymerase
A) What is the coding strand DNA coding strand?
B) What is the DNA template strand?
A) - strand that is not involved in transcription, it is the same as the new rna except RNA has uracil instead of thymine
B) It is the strand of DNA that acts as a template for rna polymerase, a strand of RNA is made that is complementary to this
What is upstream and downstream in terms of transcription?
Upstream: (5’ end) direction in which the polymerase has come
Downstream: (3’ end) direction of transcription
What is the TATA box?
- a DNA sequence that indicates where a genetic sequence can be read and decoded
- it is a type of promoter sequence which specifies to other molecules where transcription begins
- most commonly TATAAA
- it is able to define the direction of transcription and also indicates the dna strand to be read
- transcription factors can bind to the TATA box and recruit an enzyme called RNA polymerase which synthesise rna from dna
3 things that happen after transcription to form mature mRNA from pre-mRNA?
- this is what happens in eukaryotic RNA
- Capping: at the ends modified with a 5’ end cap to protect against degradation
- Tailing: 3’ poly-a tail to protect against degradation
- Splicing: Introns in the middle are chopped out and Exxon’s are stuck back together (gives the mRNA its correct sequence)
A) What is translation?
B) What enzyme does it use?
C) What template does it use?
A) decoding mRNA to build a protein or polypeptide that contains a specific series of amino acids
B) Enzymes in ribosomes
C) mRNA
What are the different types of RNA?
- rRNA (Ribosomal RNA)
- mRNA (messenger RNA)
- tRNA (transfer RNA)
- miRNA (microRNA)
- non coding rNA
A) What is the genetic code? B) What are the characteristics of it? C) What is the start code? D) what are the stop codes? E) what direction are they read in?
A) relationship between codons and amino acids
B) - Codons: triplet code
- degenerate: an Amino acid may be encoded for by more than one codon
- non-overlapping; adjacent codons do not overlap
C) AUG: marks beginning of protein, encodes: methionine
D) UAA, UAG and UGA
E) mRNA codons are read from 5’ to 3’ and specific protein from N to C terminus
Stages of Translation?
- Initiation: tRNA carrying methionine attaches to small ribosome unit, bind to 5’ of mRNA (recognise the 5’ GTP cap), scans in 5–> 3 direction until they reach the start codon (AUG) and bind to it and large subunit then binds, H bonds formed between codons and anticodon
- Elongation: the next tRNA moves into the next site (A site) and the anticodon binds to codon (via H bonds) the amino acid attached to this tRNA will form a peptide bond with the MET amino acid, then the mRNA is pulled onward through the ribosome by one codon exposing a new codon
- N to C chain growth in aminoacyl tRNAs - Termination; occurs when a stop codon in the mRNA (UAA, UAG or UGA) enters the A site
- stop codons are recognised by proteins called release factors which affect the enzyme that forms peptide bonds by adding a water molecule to the last amino acid chain, the newly made protein is released
A) what is a tRNA?
A) Transfer RNA: contains a set of three nucleotides called an anticodon which binds to mRNA complementary codon (H bonds)
- contains an amino acid which is encoded by the codons that the tRNA binds
What is the wobble hypothesis of tRNA?
- for any AA, the first 2 nucleotides in the codon are always identical, its the 3rd nucleotide that can change
- 3rd nucleotide of the codon doesn’t require the same level of binding specificity as the first 2, the 3rd ‘wobbles’ between several nucleotide possibilities
- this allows for a cell to successfully synthesis proteins without needing all codons present and can also protect against mutations as a mutation at the 3rd nucleotide has a good chance of producing the same AA (silent mutation)
- 5’ base of anticodon and 3’base of codon is the wobble position
How does the right amino acid get linked to the right tRNA ?
- enzymes called aminoacyl-tRNA synthetases recognise the AA and its tRNA
- once the AA and tRNA have attached to the enzyme the enzyme links them together using ATP
