Protein Synthesis Flashcards
What are the 4 nitrogenous base pairs in RNA?
A & U
C & G
Which base does Adenine pair with in RNA?
Uracil
Which base does Guanine pair with?
Cytosine
Which base does Uracil pair with in RNA?
Adenine
Which base does Cytosine pair with?
Guanine
What does RNA stand for?
Ribonucleic acid
What are the 4 types of RNA?
- mRNA
- tRNA
- rRNA
- Ribozymes
What are the 3 basic steps of making a protein?
- DNA is transcribed to mRNA
- mRNA travels to the cytoplasm
- mRNA is translated by ribosomes
Where does transcription occur in eukaryotes?
in the nucleus
Where does the mRNA travel to in eukaryotes?
the cytoplasm
Where do all the steps of protein synthesis occur in prokaryotes?
the cytoplasm
T or F: most genes code for a polypeptide
True
Which direction does DNA polymerase make new DNA strands and which way does it read DNA strands?
MAKES: 5’-3’
READS: 3’-5’
Define transcription
The synthesis of RNA using information in DNA
Which enzyme transcribes DNA?
RNA Polymerase
How does transcription occur?
- RNA polymerase binds to DNA at gene’s promoter
- RNA polymerase unwinds DNA and separates strands
- RNA polymerase makes RNA in the 5’-3’ direction
- Synthesizes RNA by pairing complementary RNA nucleotides with the template DNA
Define promoter
Specific DNA sequence where RNA polymerase attaches and initiates transcription
Define transcription factors
A collection of proteins in eukaryotes that help RNA polymerase bind to promoters and start transcription
What happens if there are no transcription factors present?
No transcription of genes = no proteins synthesized
How does RNA polymerase bind to DNA in eukaryotes?
Transcription factors help RNA polymerase bind to promoters and start transcription
Do prokaryotes have transcription factors?
No, they do not need help binding RNA polymerase to DNA
T or F: RNA is made in the 5’-3’ direction
TRUE
What type of bond forms between the nucleotides when RNA is being synthesized?
Phosphodiester bonds
When does RNA Polymerase detach?
When it hits a specific sequence in the DNA that signals transcription is finished
What happens when transcription is finished?
The DNA strands will rebond and recoil (hydrogen bonds) will reform between the nitrogenous bases of the ladder
What bonds reform when transcription is finished?
Hydrogen bonds between the nitrogenous base pairs
How many hydrogen bonds between G and C?
three
How many hydrogen bonds between A and U?
two
What is the product of transcription?
RNA
Either rRNA, tRNA, or mRNA
What are the final products of transcription and which product will continue on the process of translation?
FINAL: tRNA and rRNA
if mRNA is produced, it will need to be translated
Define translation
The production of a polypeptide by a ribosome reading the information encoded in an mRNA
Which form of RNA is translated?
mRNA
Essentially, what does translation mean?
It changes mRNA from the language of nucleotides to the language of amino acids
T or F: all species use the same genetic code
True
What is the genetic code?
All bases are read in groups of 3 (codon)
read by ribosomes in a 5’-3’ order
What reads the mRNA and in which direction?
ribosomes, in the 5’-3’ direction
Define gene expression
making the product (protein or RNA) that is encoded by a gene
Define codon
3 nitrogenous bases in mRNA specifying an amino acid or terminating the assembly of a polypeptide
How many different codons are there?
64 different combinations of the three bases
How many codons are there for amino acids?
61
How many stop codons are there?
3
How many amino acids exist?
20
Describe why the genetic code is degenerate?
Because most amino acids are specified by more than one codon
ie, there are 20 amino acids and 61 codons for amino acids
What is the universal start codon and which amino acid does it code for?
AUG, codes for methionine amino acid
What are the 3 stop codons?
UAA
UGA
UAG
Define start codon
Place where translation starts on mRNA.
It sets the reading frame for the codons
it is AUG (methionine amino acid) for all polypeptides
Define reading frame
The part of mRNA that is translated
It sets which groups of three nitrogenous bases are read together (ie how the codons are read)
Define anticodon
A nucleotide triplet which base-pairs wth a complementary codon on mRNA
ex. mRNA codon GGC = anticodon CCG
What is aminoacyl-tRNA synthetase?
An enzyme that attaches the correct amino acids to tRNAs
What does charging the tRNA mean?
When an amino acid is put onto the tRNA it becomes charged
How many aminoacyl-tRNA synthetases are there?
one for each amino acid = 20
What are ribosomes composed of?
two subunits made of proteins and rRNAs
What is the function of ribosomes?
to add each amino acid to the polypeptide chain
What form of RNA do ribosomes have binding sites for?
mRNA and tRNA
How many binding sites do ribosomes have for charged tRNA and what are they called?
3:
EPA
Describe the P site
The peptidal binding site on ribosomes that holds charged tRNAs that carry the growing polypeptide chain
Describe the A site
The aminoacyl-tRNA binding site on ribosomes that holds tRNA that carries the next amino acid to be added to the polypeptide chain
Describe the E site
the exit site on ribosomes where discharged tRNAs leave
What are the 3 steps of translation?
- Initiation
- Elongation
- Termination
What occurs during the initiation step of translation?
- small ribosomal subunit binds to mRNA at start codon
- tRNA charged with methionine (AUG) binds to mRNA at P site
- large ribosomal unit attaches
this is all powered by the hydrolysis of GTP (Guanosine triphosphate)
What occurs during the elongation step of translation?
Amino acids are added one by one to the growing chain in a three step cycle
- appropriately charged tRNA comes into A site and forms H-bond between codon and anticodon
- peptide bond is formed between growing chain and incoming amino acid
- polypeptide is transferred to tRNA in A site
What occurs during the translocation step of translation?
- mRNA moves down three bases so that
- tRNA that was in the P site moves to the E site where it is released
- tRNA that was in A site is now in P site
- next codon is now in A site
When does translation end?
When the stop codons are reached (UGA, UAA, UAG)
What occurs during the termination step of translation?
- UAG, UAA, UGA are stop codons that do not code for an amino acid
- when these codons reach the A site, release factor proteins bind to the stop codon
- polypeptide is released by release factors
- small and large ribosome subunits separate
Define release factors
Proteins in the termination stage of translation that bind to the stop codon by hydrolyzing the bond between the last amino acid and tRNA in the P site to release the polypeptide
