replication
DNA copying
transcription
DNA->RNA
translation
RNA->protein
Steps of protein synthesis Advanced
RNA made from DNA as a template
RNA is spliced into mRNA (introns (nonsense RNA) taken out, exons kept)
mRNA is moved outside the nucleus to the ribosome
Codons on mRNA is matched up with anticodons on tRNA
tRNA codons carry an amino acid based on its triplets
The amino acid is added to the growing chain of amino acids creating a protein
When finished the amino acid chain leaves the ribosome and is moved to its target area.
Mutation
A change in the DNA code that changes the protein being made
Can be beneficial, detrimental or neutral
Spontaneous mutations = natural reaction in the organism (no cause)
Induced mutation = due to exposure to UV-light, chemicals or other environmental agent
Are normally permanent
Can be inherited, but not always
Point mutation
Change in one single base in the DNA sequence
Also known as single substitution
mutation
Substitution mutation
Can be a single point mutation (previous slide)
Can be several bases
Inversion
When a part/segment of a mutation is reversed
Insertion
When a new base or segment is added in
Causes a frameshift, which
makes the protein different
Deletion
When a base or a segment is removed
Causes a frameshift
Silent mutation
No change in the amino acids/proteins being produced
Missense mutation
The amino acid sequence changes
Nonsense mutation
Creates a STOP in the amino acid sequence, which gives a change in function
Frameshift mutations
changes where the reading of the code starts and ends and can change the amino acid chain/protein dramatically
Steps of Protein synthesis simplified
Transcription: the DNA sequence/gene is copied, substituting T for U
Translation: the mRNA sequence is matched in the ribosome with tRNA carrying an amino acid. Bases are read as triplets.
mRNA
Messenger RNA, is the copy of the gene, produced/found in the nucleus, flat shape
tRNA
Transfer RNA, is the link between mRNA and amino acids, carried one amino acid, found in cytoplasm, hairpin shape
rRNA
Ribosomal RNA, found in the ribosome, part of the ribosome’s structure, globular
RNA modification
Before going on to the ribosome the RNA needs to be modified.
Introns are being spliced out, exons are expressed so they are kept.
Spliceosome is responsible for splicing.
Alternative splicing: gives a single gene an option to make several different proteins.
mRNA Protection
The mRNA has to be protected from digestive enzymes in the cytoplasm. Does this in two ways:
Capping: addition of modified guanine, protects from digestive enzymes, helps attach to the ribosome
RNA Messaging Key
Introns removed- REFINES MESSAGE!
Alternative Splicing -MAXIMIZE MESSAGE -to create different protein recipes from same mRNA.
Capping and Tailing – PROTECTS THE MESSAGE!
Translation Stages
Initiation: tRNA starts the coding based on the start codon - AUG
Elongation: amino acids are joined together one-by-one with covalent bonds
Termination: a stop signal is reached on the mRNA and the new polypeptide chain detaches.
Stop codons: UAA, UAG, UGA
Codes that starts with a U it is most likely a stop codon
Codons
a mechanism where the message is read in triplets – what we call “codons”
Codon – the triplet of bases on the mRNA that correspond to a particular amino acid
Anti-codon – the complimentary triplet of bases on tRNA that brings a specific amino acid to the ribosome
Gene Regulation
Only 2% of the human genome actually codes for something, as far as we know
A lot of DNA seems to have come from viruses
This explains the need for splicing
Promoters and enhancers
Promoter sequences: non-coding DNA, longer
“Shows” where transcription for RNA starts
Very often known as the TATA box
Located 25-35 bases away from the start of the actual gene
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Enhancer sequence: non-coding DNA, shorter
Enhances the rate of transcription = makes transcription faster