Lecture 11 - test 3 Flashcards
What is a gene?
A sequence of bases in a DNA molecule that carries information for making proteins.
What is a genome?
An organisms complete set of DNA.
Does all DNA contain instructions for making proteins?
No.
How big is human’s genome compared to an amoeba?
Small.
What are introns?
Non-coding DNA within genes.
How does DNA turn into a protein?
DNA is transcribed to RNA and RNA is translated into a protein.
What is transcription?
When the gene’s sequence is copied from DNA to a middleman molecule called RNA. (DNA -> RNA)
What is translation?
When the gene’s sequence is encoded in mRNA, which directs the production of a protein. (RNA -> protein)
What violates the order of central dogma?
Viruses.
What are the steps of transcription?
- Recognize and bind
- Transcribe
- Terminate
- Cap and process
What happens during the first stage of transcription?
The RNA polymerase recognizes a promoter site and binds to one strand of the DNA.
What happens during the second stage of transcription?
The DNA strand goes through the RNA polymerase and it builds a single strand RNA copy of the gene, called mRNA transcript.
What happens during the third stage of transcription?
The RNA polymerase encounters a code that tells it to stop transcribing and releases the mRNA.
What happens during the fourth stage of transcription?
A cap and tail is put on the mRNA for protection and to promote recognition and the non-coding sections are removed.
What are the steps of translation?
- Recognition and initiating protein building
- Elongate
- Terminate
What happens during the first stage of translation?
The start sequence of the mRNA is recognized and the tRNA attaches, with the ribosomal subunits assemble.
What happens during the second stage of translation?
The tRNA molecule binds to the mRNA and then floats away.
What happens during the third stage of translation?
The ribosome encounters the stop sequence and the mRNA is released.
What nitrogen base in DNA is replaced in RNA?
T (thymine) is replaced by U (uracil).
What does RNA polymerase creat?
RNA.
What is RNA made of?
RNA nucleotides.
What are 3 requirements for transcription?
- A promoter
- A start site
- A termination site
Wha is a promoter?
It forms a recognition and binding site for the RNA polymerase and is found in front of the start site. It is not transcribed.
What are 2 forms of RNA polymerase?
- Core polymerase
- Holoenzyme
What is the holoenzyme for?
It is needed to accurately initiate synthesis.
What direction does transcription elongation occur?
5’-3’
What is a transcription bubble?
It contains an RNA polymerase, DNA template, and growing RNA transcript.
What happens after the DNA is transcribed and leaves the transcription bubble?
It rewinds into the double helix.
What nucleotides pair together?
C to G
A to T (or U in RNA)
What happens when transcription is terminated?
A hairpin is formed when the RNA joins with itself and pokes the polymerase to release the RNA.
What is an operon?
A single mRNA that contains multiple genes in prokaryotes.
What is different about transcription and translation in prokaryotes?
They occur at the same time.
What does RNA polymerase I transcribe?
rRNA.
Wat does RNA polymerase II transcribe?
mRNA and some snRNA.
What does RNA polymerase III transcrib?
tRNA and some other small RNAs.
What is the initiation complex?
When the RNA polymerase II associates with the transcription factors.
What are mRNA modifications that occur in eukaryotes?
- A 5’ cap is added
- A 3’ poly-A tail is added
- Introns are removed
What are introns?
non-coding sequences.
What are exons?
Sequences that will be translated.
What are snRNPs?
small ribonucleoprotein particles that form spliceosome and removes introns.
What is pre-mRNA splicing?
When the introns are removed.
What is alternative splicing?
When a single primary transcript is spliced intro different mRNAs by exluding different sets of exons.
What does alternative splicing explain?
How humans have only 20,000 genes, but can encode 93,000 proteins.
How is the order of amino acids determined?
By the order of nucleotides in DNA and RNA.
What is a codon?
A block of 3 DNA nucleotides corresponding to an amino acid.
Are amino acids only specified by one codon?
No there are 64 possible codons and only 20 amino acids, so more than one codon specify only one amino acid.
Can one codon code for more than 1 amino acid?
No.
What are 2 types of special codons?
Stop codons and start codons.
How is tRNA used in the process?
It brings amino acids to be added to a protein.
What do aminoacyl-tRNA synthetases do?
Add amino acids to the acceptor stem of RNA.
How many subunits do ribosomes have?
Large and small.
What are the tRNA-binding sites on ribosomes?
- E site
- P site
- A site
What is the E site on a ribosome?
It binds the tRNA that carries the previous amino acid added.
What is the P site on a ribosome?
It binds the tRNA attached to the growing peptide chain.
What is the A site on a ribosome?
It binds the tRNA carrying the next amino acid site.
What are two primary functions of ribosomes?
- Decode the mRNA
- Form peptide bonds
What is peptidyl transferase?
It forms peptide bonds between amino acids.
What is translation?
The creation of proteins.
What are requirements of translation?
- Ribosomes
- mRNA
- tRNA
- Amino acids
What do ribosomes do in translation?
They decode the mRNA and create the protein.
What do mRNA do in translation?
They code for the amino acid order.
What do tRNA do in translation?
They bring the correct amino acid to be added.
What do amino acids do in translation?
They are the building blocks of proteins.
In prokaryotes, what makes up the initiation complex?
- Initiator tRNA charged with N-formylmethionine
- Small ribosomal subunit
- mRNA strand
What happens in prokaryotic translation?
The ribosome binding sequence of mRNA positions small subunit, the large subunit is added, and the initiator tRNA binds to the P site.
How is eukaryotic translation different from prokaryotic translation?
- The initiating amino acid is methionine
- It is a more complicated process
- Lack of an RBS (ribosome binding sequence)
What is elongation in translation?
When amino acids are added.
What happens in elongation?
The second tRNA binds to the empty A site, EF-Tu bind to tRNA and GTP and a peptide bond is formed. Amino acids are added as the cycle continues.
What is the elongation cycle?
- The tRNA anticodon is matched with the mRNA codon
- The peptide bond is formed
- Ribosomes are translocated
What is wobble pairing?
When there are fewer tRNA’s than codons.
What does wobble pairing accomplish?
It allows less stringent pairing between the 3’ base of the codon and the 5’ base of the anticodon, which allows fewer tRNAs to accommodate all codons.
What is the translation termination?
When the ribosome encounters a stop codon, which releases the polypeptide chain.
