week 19 Flashcards
what two factors damage DNA
high energy radiation and chemicals (mutagens)
describe mitochondrial DNA
mtDNA is found near the membrane, is double-stranded and circular and codes for proteins in the respiratory chain. It is passed through generations through maternal lineage.
describe the difference between RNA and DNA
RNA has ribose instead of deoxyribose and uracil instead of thymine.
how is the RNA transcript modified before it leaves the nucleus
A cap (modified form of G) is added to 5’. A polyA tail is added to the 3’. This protects mRNA from degradation, aids export from the nucleus and helps the mRNA to anchor to ribosomes.
what do nuclear ribonucleoproteins (snRNPs) do
splice out the non-coding regions (introns)
what marks the splice sites on introns
short nucleotide sequences at the end of introns
how is DNA replication made to be a rapid and accurate process
specific base pairing (a-t and g-c) and proofreading. All DNA polymerases have proofreading and detect and remove incorrectly added bases.
what catalyses transcription
the enzyme RNA polymerase, which unwinds the double helix structure and makes a complementary copy
what benefit does splicing have
it helps to increase the range of possible protein products from a gene
what are the stages of transcription
initiation, elongation and termination
describe initiation in transcription
initiation is a site known as a promoter containing a particular sequence of bases. RNA polymerase binds to the promoter.
describe elongation in transcripton
unwinding of the DNA as nucleotides are added and rewinding of DNA after added nucleotides.
describe termination of transcription
appears to be signalled by a sequence of the RNA transcript. after the termination sequence is transcribed, proteins bind to the transcript and cut it from the polymerase. the transcript is released, and the RNA polymerase detaches from the DNA.
what are the types of RNA
mRNA (mitochondrial), rRNA (ribosomal), tRNA (transfer) and small nuclear RNA
what does tRNA do
transfers amino acids to the site of protein synthesis, a ribosome. there are different types of tRNA for each of the 20 amino acids.
describe initiation of translation
30 S subunit of ribosome binds to mRNA at the start codon. an initiator tRNA carrying amino acid Met binds to start codon on mRNA. 50 S ribosome subunit binds forming initiation complex. protein initiation factors + energy are required.
describe elongation of translation
amino acids added one at a time, peptide chain grows from amino towards carboxyl end.
1. codon recognition- bringing correct aminoacyl-tRNA
2. peptide bond formation- new amino acid is joined to growing peptide chain, catalysed by rRNA
3. translocation- ribosome moves tRNA in A site to the P site
what is translocation is translation
stage in elongation. ribosome moves tRNA in A site to the P site. discharged tRNA in P site is moved to E site to leave ribosome requiring energy (GTP)
describe termination of translation
elongation continues until a stop codon appears in A site of the ribosome. the peptide chain is released.
what is the composition of ribosomes
2 subunits- large (50 S) and small (30 S). The two subunits only join when mRNA is present. rRNA is a key component of ribosomes.
what are the binding sites on ribosomes used for translation.
- mRNA binding site (30 S)
- P site (50 S)= binds the growing peptide chain
- A site (50 S)= binds tRNA bound to an amino acid
- E site (50 S)= exit site which discharges the tRNA to leave ribosome
what is aminoacyl- tRNA synthase
required enzyme to load the correct amino acid onto the correct tRNA.
what do polyribosomes do
multiple ribosomes bound to one mRNA allowing multiple copies of polypeptide chains to be made simultaneously from the same mRNA transcript.
what is the genetic code
used for translating nucleotide language into amino acid language, showing the different amino acid possibilities which could be produced from each mRNA sequence
what are post-translational modifications
- protein folding- chain has to fold to its correct 3D structure required for its function.
- other components e.g. sugars or lipids may be added or some amino acids may be removed.
- protein may have to move to its required location (proteins that leave the cell, membrane proteins)
what is proteolytic cleavage
process of breaking/ cleaving peptide bonds between amino acids in proteins. this is a form of post translational modification.
what three main bonds hold a proteins shape
hydrogen bonds, ionic bonds and hydrophobic bonds
what is the primary structure of proteins
the amino acid sequence
what is the secondary structure of proteins
the way the backbone folds, stabilised by hydrogen bonds. these form alpha helices and beta sheets
what is the tertiary structure of proteins
ways the polypeptide folds into a 3D shape stabilised by hydrogen and ionic bonds, hydrophobic interactions and disulfide bonds involving backbone and sidechain groups
what is the quaternary structure of proteins
the arrangement of subunits in proteins containing two or more polypeptide chains
how is the peptide bond formed
condensation (loss of water) between the amino acid and the carboxyl group
what are oligopeptides
polypeptide chains of less than 20 amino acids
what bonds do non-polar, charged and polar sidechains of polypeptides form
non-polar side chains- hydrophobic interactions
charged side chains- ionic bonds
polar side chains- hydrogen bonds
how do proteins usually fold in relation to side chains
hydrophobic groups fold inside while charged and polar groups fold outside.
what is de novo protein synthesis
creating proteins designed for specific purpose
what do weak interactions which hold protein shape imply
- protein conformation is flexible- structure can change often conformational change is essential for function.
- protein conformation can be easily destroyed e.g. denatured
- function of many proteins can be regulated by events that cause conformational change of the protein.
what are chaperone proteins
proteins which help proteins in the cell to fold up properly
what are protein domains
independently stable parts of the polypeptide which serve a specific function for the protein. evolution of new proteins can occur via domain-swapping
what is induced fit
enzymes active site changes shape when it binds to its substrate
what is the structure of antibodies
two heavy and two light polypeptide chains joined by disulphate bridges.
what is the epitope of an antigen
a small part of the antigen which an antibody recognises
