Transcription
In eukaryotes, what must bind to the promoter before RNA polymerase can start transcription?
What are Transcription factors.
The organelle where translation occurs.
What is the ribosome?
What type of mutation changes one nucleotide but does not change the amino acid?
What is a silent mutation?
Operons are a feature of which type of cell?
What are prokaryotic cells?
How do mRNAs allow one gene to make multiple proteins?
Through alternative splicing, which combines exons in different ways.
After transcription, what modifications occur to the pre-mRNA before it leaves the nucleus?
What are:
What happens in the P site of translation in the ribosome?
What is the growing polypeptide chain is formed.
What type of mutation adds or moves nucleotides and shifts the reading frame?
What is a frameshift mutation?
What happens to the TRP operon when tryptophan levels are high?
Tryptophan activates the repressor, which binds the operator and stops transcription.
Describe how chromatin structure impacts transcription initiation
Euchromatin is necessary for transcription. Heterochromatin blocks access.
What's the function of the TATA box?
It's a specific promoter sequence that helps position RNA polymerase correctly to start transcription.
What happens when a ribosome reaches a stop codon?
A release factor binds, translation stops, and the polypeptide chain is released.
What type of mutation changes the amino acid but keeps similar properties of the amino acid?
What is a conservative missense mutation?
What is the function of the operator in an operon?
It is the DNA site where a repressor binds to block transcription Or where the activator binds to increase transcription.
What effect does histone acetylation generally have on transcription?
It loosens chromatin and increases transcription.
What would happen if a eukaryotic cell lacked the ability to add a 5' cap to pre-mRNA?
The mRNA would degrade quickly because it couldn't attach to the ribosome, preventing translation.
Why does it matter that multiple codons can code for the same amino acid?
It reduces the effect of mutations, since many base changes don't alter the amino acid.
If a tRNA's anticodon mutates but the attached amino acid stays the same, what might happen?
The tRNA could pair with the wrong codon, inserting the wrong amino acid, and producing a misfolded protein.
Predict what happens to the lac operon if the gene LacI is deleted.
The operon is always on because no repressor protein is made
What is the purpose of microRNAs and eukaryotic cells?
They bind to mRNA and block translation or cause degradation.
In a eukaryotic gene, the enhancer sequence is located thousands of bases upstream from the promoter. How does it still influence transcription?
DNA can loop so that activator proteins bound to the enhancer interact with transcription factors and RNA polymerase at the promoter, increasing transcription initiation.
What are the distinct roles of the large and small ribosomal subunits during translation?
The small subunit binds to the mRNA and scans for the start codon, aligning the initiator tRNA. The large subunit provides the P-site that catalyzes peptide bond formation.
Explain how a mutation in a regulatory gene, such as one coding for a transcription factor, can have a broader effect than a mutation in a structural gene.
A mutation in a regulatory gene can alter the expression of MANY downstream target genes, disrupting entire pathways or cellular processes. While a structural gene mutation affects only one protein.
Explain how the Lac operon integrates signals from both lactose and glucose to control transcription.
When lactose is present, it inactivates the repressor, allowing transcription.
When there is low glucose, it increases cAMP, which binds to CAP to enhance RNA polymerase binding.
When there is high glucose, there is low cAMP and CAP is therefore inactive, making for low transcription.
This ensures that glucose is the preferred energy source.
How can environmental factors alter gene expression without changing DNA sequence?
Epigenetic modifications like DNA methylation or histone modification that activate or silence genes in response to external signals.