What is a codon?
A codon is a nucleotide triplet that encodes for a specific amino acid
Why is the genetic code redundant?
Because some amino acid are encoded by more than one codon
Why is the genetic code non ambiguous?
Because one codon can specify only one amino acid
What are the three functions of tRNA?
1) tRNA binds to a particular amino acid to become charged 2)tRNA binds to a mRNA at a region called the anticodon. 3) tRNA interact with ribosomes
What is a ribosome?
A molecule that contain RNA and it's composed of two subunits.
What are the two subunits of the ribosome?
Large subunit and Small subunit
Describe the large subunit
Consists of 3 different molecules of rRNA and 49 different proteins.
Describe small subunit:
Consists of 1 rRNA molecule and 33 different proteins.
Describe A site:
A stands for amynoacil and is where the charged tRNA anticodon binds to the mRNA codon.
Describe the P site:
P stand for peptidyl and is where the tRNA adds its amino acid to the polypeptide chain.
Describe E site:
E stands for exit. After tRNA gave up its amino acids it is released from this site.
What are the three phases of translation?
1) Initiation 2) Elongation 3) Termination
Describe Initiation of translation:
1) The initiation complex is formed. 2) The anticodon and the start codon bind via complementary base pairing. 3) The large subunit join the complex
Describe Elongation of translation:
1) a charged tRNA whose anticodon is complemenary to the second codon of mRNA enters the A site. 2) The large subunits catalyze the peptydil transferase activity. 3)The first tRNA releases its amino acid chain and moves to the E site where it dissociate from the ribosome. 4) The next tRNA is shifter to the P-Site and the ribosome moves one codon along.
Describe termination of translation:
A stop codon enters the A site, it doesn't corresponds to any amino acid and they don-t bind to any tRNA. Instead, they bind a protein release factor that allows the hydrolisis of the bond between the polypeptide chain and the tRNA in the P-site.
What are the two reaction that form the peptidyl transferase activity?
1) It breaks the bond between tRNA and its amino acid in the P-site. 2) It catalyze the formation of a peptide bond between the amino acids on the P and on the A sites.
What are polyribosome:
Several ribosomes that work simultaneously on the same mRNA translating and producing multiple polypeptide at the same time.
What are the two possibile paths that a protein can take when it's synthesised?
It can either complete the trnalsation and being release to an organelle (or remain in the cytosol) or stop translation, go to the endoplasmic reticulum and finish synthesis there.
What are the three different post-translational process
1) Glycolisation 2) Proteolysis 3) Phosphorilation
Cutting of a polypetide chain catalysed by protease.
Additioon of a sugar to protein to make glycoprotein.
Addition of a phosphate group to protein catalysed by kinases.
What are restriction endonucleases?
Enyzmes that cut DNA at specific sequences and create sticky ends.
Describe DNA ligase:
Enzyme that join the 5' end of one polynucleotide to the 3' end of another polynucleotide.
What is recombinant DNA?
A DNA molecule that has been made in laboratory using at least different sources of DNA.
What are plasmids?
Small circualr DNA molecules that replicate autonomously in many prokaryotes.
What are the three characteristics of plasmids?
1) An origin of replication that allow the plasmid to reproduce. 2) Selectable marker genes (usually antibiotics). 3) Unique restriction endonucleases sites for the insertion of a DNA fragment.
What are homopolymers?
Nucleic acids or polypeptides that contain a single type of subunit
What are heteropolymers?
Nucleic acids or polypeptide that contain more tha one class of subunits