Protein Synthesis Flashcards
A, P, and E Sites
A Site: Aminoacyl site, where the new tRNA carrying an amino acid binds which adds amino acid to the growing polypeptide chain
P Site: Peptidyl site, which holds the tRNA during peptide bond formation
E Site: Exist site, where tRNA that lost their amino acid leaves the ribosome
Proteasomes
An enzyme that breaks down cells that no longer function or aren’t needed
Structure of Ribosomes
Made of proteins and rRNA
Has large and small subunit, large subunit has three binding sites for tRNA molecules (A, P, E). Small subunit has a binding site for mRNA
Sickle Cell Anemia Altered RBC
DNA sense strand is GTG
DNA template strand is CAC
mRNA is GUG
Valine which is hydrophobic and makes hemoglobin less soluble
Sickle Shaped
Transcription
The process of copying DNA into mRNA in the nucleus
Alternative Splicing
A process during gene expression where a single gene codes for multiple proteins
Amino Acid and Bases
There are 20 amino acids, and only 4 bases. Since the bases are read in groups of 3, this gives 4^3 or 64 combinations which is more than enough to code for 20 amino acids
Before Initiation
tRNA activating enzyme links amino acid to the specific tRNA with the matching anticodon
Differences with Coding and Non-Coding RNA
Coding is identical to RNA
Non-coding is complementary to RNA
Coding serves as a reference for mRNA formation
Non-coding doesn’t participate in protein synthesis
Coding is 5’ to 3’
Non-coding is 3’ to 5’
Post-transcriptional Modification
In eukaryotes, the mRNA has to undergo modification in order to become mature mRNA before it exits the nucleus
The non-coding introns are removed from the mRNA through RNA splicing, therefore having mature mRNA
mRNA gets addition of methyl group at the 5’ end called capping which provides protection against degradation by enzymes
mRNA gets addition of long chain of adenine bases at the 3’ end called polyadenylation which stabilizes RNA and facilitates its export outside the nucleus
Consequences of Sickle Cell Anemia
Insoluble hemoglobin can’t effectively carry oxygen, so less respiration
Hemoglobin tends to crystalize which causes them to be less flexible and get stuck in capillaries to restrict blood flow
Sickle cells get destroyed more rapidly than normal RBC”s
Susceptible to infections
Non-coding Sequences in DNA
Promotors and Enhancers and Silencers
Introns
Telomeres
Stop Codons
UAA
UAG
UGA
Post-translational Modification
Polypeptides get modified to make them fully function. Examples of modification include
Removal of methionine from 5’ end
Changes to side chains of amino acids
Folding of polypeptide or combining two or more polypeptides
Genetic Code
A set of rules by which information encoded in mRNA sequences is converted into proteins
Sickle Cell Anemia Normal RBC
DNA sense strand is GAG
DNA template strand is CTC
mRNA is GAG
Glutamic acid which is hydrophilic which helps hemoglobin be soluble
Biconcave Disc
Process of Transcription
RNAP binds to promotor site which separates DNA into 2 strands, and exposing DNA bases for pairing
Only 1 strand will be used for replication
RNAP slides along the template strand and synthesizes the new RNA strand by complementary base pairing
A = U, C = G
RNAP then links the nucleotides together through covalent bonds, then ends transcription when it reaches terminator region of the gene
RNA breaks away from the DNA template strand, and DNA strands rejoin to form a double helix, then the RNA strand diffuses through the nuclear pore into the cytoplasm
Process of Translation
Consists of 3 stages: Initiation, Elongation, and Termination
Initiation is where the mRNA binds to the small subunit of the ribosome at the 5’ end, and slides across the mRNA to the start codon. The tRNA binds to the small subunit of the ribosome and binds to mRNA through complementary base pairing. Large ribosome then binds to smaller one.
Elongation is where the second tRNA pairs with the next codon at the A site. The two amino acids join by a peptide bond. This causes a shift, making the first tRNA go to the E site and exiting the ribosome, and the second tRNA to go to the P site. Another tRNA pairs with the mRNA at the A site, and the process continues and the polypeptide becomes longer until a stop codon is reached.
Termination is when a stop codon is reached, which triggers the termination of translation as no tRNA have a complementary anticodon. A protein called the release factor fills up the A site to forcefully shift the last tRNA into the E site thus releasing it, and the mRNA detaches from the small sub-unit, and the small and large sub-unit separate
Activators and Repressors
Activators bind to Enhancers to increase transcription
Repressors bind to Silencers to decrease transcription
Translation
The synthesis of polypeptides with a specific amino acid sequence that is determined by their base sequence on the mRNA molecule
Occurs in cytoplasm and requires tRNA, mRNA and ribosomes
Transcriptome
The full range of RNA types made in a cell, and changes based off the activity of the cell
Role of tRNA
Carries amino acids to the large subunit of the ribosome and matches them to the coded mRNA nucleotides to be assembled into proteins
Role of mRNA
Has a site that can bind to the small subunit of the ribosome with a star and stop codon to indicate where translation begins and ends
Role of Ribosomes
Use the sequence of codons in mRNA to assemble amino acid into polypeptide chains
Transcription and Translation in Prokaryotes VS Eukaryotes
DNA is found in the cytoplasm
DNA is found in the nucleus separated from the cytoplasm
Both transcription and translation take place in the cytoplasm
Transcription takes place in the nucleus and translation in the cytoplasm
Transcription and translation are continuous
Transcription and translation are discontinuous
No modifications occur
Post transcriptional modifications occur
Genes do not have introns
Genes have non-coding regions called introns which are removed to produce mature mRNA
Translation in Prokaryotes and Eukaryotes
In prokaryotes. translation occurs immediately after transcription due to the absence of a nucleus
In eukaryotes, translation occurs after the mRNA transports from the nucleus to the ribosome
Types of Genetic Code
Linear: Read in one direction
Degenerate: More than one codon for an amino acid
Universal: The same base sequence always codes for the same amino acid
Punctuation: Start and Stop codons which initiate and end translation
Transcription VS Translation
DNA gets transcribed
RNA gets translated
Takes place in nucleus
Takes place in cytoplasm (ribosome)
mRNA is produced
Polypeptide is produced
