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What are the three types of RNA?
mRNA, rRNA, and tRNA
What does mRNA stand for?
Messenger
What does rRNA stand for?
Ribosomal
What does tRNA stand for?
Transfer
What does mRNA do?
The base sequences of mRNA carries the information for the amino acid sequence of a protein
What does rRNA do?
rRNA combines with proteins to form ribosomes
What does the small subunit of the ribosome bind to?
The 5’ cap of the mRNA
What does the large subunit of the ribosome bind to?
The tRNA
What does the large subunit of the ribosome do?
Catalyzes peptide bond formation between amino acids during protein synthesis
Where is rRNA synthesized?
In the nucleolus
Do the two subunits enter the nucleolus and nucleus separately or already bind together?
Separately
They bind together in the cytoplasm
What does tRNA do?
Transports amino acids to the ribosome
How many types of tRNA are there?
At least one type assigned to carry each of the 20 different amino acids
How many amino acids are there?
20 different AA’s
What does the tRNA bind to?
The anticodon of the tRNA pairs with a codon of mRNA, ensuring that the correct AA is incorporated into the protein
What is the key to the genetic code?
The sequence of bases within a DNA strand
The four bases can be arranged in any order, and this sequence is what codes genetic information
What is an analogy for the genetic code?
The english language, 26 letters, unlimited combinations of words and letters
What does the genetic code translate?
The sequence of nucleotides in mRNA (copied from DNA) into a specific amino acid sequence
What are the bases in mRNA read by?
The ribosome in triplets of bases (codons)
What does a codon specify?
A unique amino acid in the genetic code
What is always the first codon in an amino acid sequence?
The start codon
What is always last in an amino acid sequence?
A stop codon
What is an anticodon?
3 exposed bases on the tRNA
What does the anticodon do?
Pairs with a complementary mRNA codon
Is an amino acid specified by only one codon?
One amino acid can be specified by more than one codon
Why is an amino acid’s ability to be specified by more than one codon beneficial?
Avoids mistakes
Can a codon specify more than one amino acid?
A codon specifies only one amino acid
Do codons stand for the same amino acids in all living things, or are there different codons for different organisms?
The genetic code is universal, which means the codons stand for the same amino acids in all living things
What does the genetic code being universal prove?
All living things come from a common ancestor
What are the steps to translation?
Initiation, elongation, and termination
How does initiation work?
The mRNA binds to the small ribosomal subunit
The mRNA slides through the subunit until AUG is exposed in the P tRNA binding site
The first tRNA containing methionine binds to the mRNA start codon
The large subunit plops on top
mRNA binds to small subunit
mRNA slides until AUG
tRNA with met binds to mRNA
Large subunit binds to everything
What does the P site stand for?
Polypeptide
What does the A site stand for?
Amino acid
What does the E site stand for?
Exit
Why does initiation use GTP?
The cell uses energy to put the large subunit of the ribosome on top of the small subunit and mRNA
What does GTP stand for?
Guanosine triphosphate
What does GTP turn into to be used for energy?
GTP → GDP + Pi + energy
What happens in elongation?
A second tRNA binds to the A binding site next to the first tRNA in the P side
A peptide bond is formed between AA’s through a dehydration reaction
The first AA is released from the first tRNA, and links to the second tRNA
The ribosome moves down the mRNA by one codon (3 nucleotides) from the 5’ to 3’ direction
The frist tRNA is now in the E site and leaves the ribosome
This cycle continues where tRNA enters the A site, pairs with codons, brings an amino acid, grows the polypeptide chain, the ribosome moves, then the tRNA exits
What steps in elongation use GTP?
A peptide bond forming between amino acids
The ribosome moving down the mRNA by one codon
What happens to the tRNA after it hands off it’s amino acid and exits the ribosome?
It is recycled and reloaded with amino acids by enzymes in the cytoplasm
How many tRNA’s can be in the ribosome at one point?
Max 2
What is transrelocation?
The ribosome moving down the mRNA by one codon (3 nucleotides) from the 5’ to 3’ direction
What are the steps to termination?
When a stop codon on the mRNA slides into the ribosome, a stop factor binds to the stop codon and translation stops
The ribosome breaks into separate subunits
The finished protein is released
What is a release factor and what does it do?
A special type of protein that cleaves the peptide off the rRNA by hydrolysis
What happens to the protein after termination?
It continues folding into a final 3D shape, which gives it a function
What part of termination uses energy?
Breaking the ribosome into subunits
What does a gene in DNA do?
Codes for a protein
What does transcription produce?
An mRNA strand complementary to the DNA template strand
What does the mRNA attach to in translation?
The ribosome
What do tRNA’s carry?
Amino acids
What is the order of tRNA based off of?
The pairing of codon and anticodon
What determines amino acid order?
Codon order
If this is the DNA strand, what will the protein? How do you go from a code to a protein?
First ensure you have the template strand
In this example, you must create the template strand (RNA polymerase reads 3’ to 5’ and we were given a strand that is 5’ to 3’ so we must make a complimentary DNA strand first)
We then make the mRNA strand, which is complimentary to the template strand (which should be 3’ to 5’)
Find AUG, then start translating the codons into amino acids
Black is what we were given, red is explained above
