Protein synthesis Flashcards
Explain TranscriptioN
- Complementary base pairing underlies it
- Resembles DNA replication with 2 main differences :
- product = RNA not DNA
- Copies just 1 gene from one DNA strand rather than copying both strands of the entire chromosome
Explain stage 1 of transcription
- Initiation
- Helices unzip the DNA double helix, exposing the template strand
- RNA Polymerase ( enzyme that builds RNA chain ) binds to the promoter
- Promoter = a DNA sequence that signals the genes start
Explain stage 2 of transcription
- Elongation
- RNA polymerase moves along the DNA template strand from3’-5’ direction, adding nucleotides ( in nucleus ) only to the 3’ end of the growing RNA molecule according to the base pairing rules
Explain stage 3 of transcription
- Termination
- Signals the end of the gene
- Upon reaching the terminator sequence the RNA polymerase enzyme separates from the DNA template and releases the newly synthesised RNA
-The DNA molecule then resumes its usual double helix shape
- The RNA molecule is synthesised and it curls into a 3D shape dictated by complementary base pairing rules within the molecule
- Final shape determines the function of the RNA molecule
What happens between transcription and translation
mRNA strand is processed
Explain the processing of mRNA
- mRNA is in nucleus which is surrounded by a membrane which prevents mRNA strand from leaving and being translated immediately
- In eukaryotes the mRNA is usually altered before it leaves the nucleus
Explain 5’cap and poly A tail in mRNA processing
- Add a cap to 5’ end and poly A tail to 3’ end = first step
- enhances translation and allows mRNA molecule to last longer
- Poly A tail = adding 100-200 adenines to 3’ end ( assists in preventing immediate degrading )
Why does the mRNA strand have to be processed in eukaryotic cells
To assist the mRNA during protein synthesis in that it will allow the mRNA strand to be held firmly by ribosome and allows it not to degrade immediately
Explain the intron removal of mRNA processing
- The removal of some parts of mRNA molecule
- In archaea and eukaryotes only part of the mRNA molecule has the info that produces the protein
- An mRNA molecule consists of alternating sequences called introns and exons
- Small catalytic RNAs and proteins remove the introns from the mRNA molecule
Remaining portions, the exons (coding DNA), are (joined) spliced together to form the mature RNA that leaves the nucleus to be translated
What are introns and exons
- Introns = noncoding parts of DNA which are removed before translation
- Exons = coding DNA which helps tell us which amino acids are needed
How does mRNA become a protein
How is mRNA made?
- Codons on mRNA are sets of 3 nucleotides
- Each codon refers to a specific amino acid
- Chains of amino acids make up the proteins
- mRNA tells us in what sequence amino acids must be added to make proteins
What is the genetic code
- Links the codon to a specific amino acid
- Start codon
- Stop codon
- Duplication of codons for the same amino acid.
- Universal
What does translation require
- A physical location ( ribosomes )
- Ribosomes have 3 important sites
- mRNA must attach to the ribosomes
- tRNA - these will bring amino acids to the ribosomes
Explain translations building the protein
- The genetic code is a set of ‘rules’ by which a cell uses the codons on the mRNA to assemble amino acids into a protein
- A codon, serves as the information for each amino acid. Each codon is a group of mRNA bases corresponding either to one amino acid or to a start or stop codon/signal
- Proteins composed of only 20 different amino acids in different sequences
- If a codon codes for amino acids it would mean that we would require a certain number of nucleotides combinations to code for all these amino acids
What are the 3 properties of genetic code
- Degenerate
- Unambiguous / absolute
- Universal
