Transcription And Translation Flashcards
What are the two major stages of protein synthesis directed by DNA?
- Transcription: Formation of RNA from a DNA template.
- Translation: Synthesis of a polypeptide using instructions from mRNA.
What are the three major types of RNA and their functions?
- mRNA (messenger RNA): Carries genetic information from DNA to ribosomes.
- rRNA (ribosomal RNA): Combines with proteins to form ribosomes.
- tRNA (transfer RNA): Transfers amino acids to ribosomes during protein synthesis.
What are ribosomes composed of?
Two subunits (small and large) made of rRNA and proteins, which assemble only when attached to mRNA.
Why can proteins not be translated directly from DNA in eukaryotes?
DNA is located in the nucleus, while translation occurs in the cytoplasm. RNA acts as an intermediate.
What is meant by the genetic code being ‘universal’ or ‘almost universal’?
The genetic code is shared by nearly all organisms, meaning the same codons specify the same amino acids across species.
What are the three main steps of transcription?
- Initiation: RNA polymerase binds to the promoter, starting RNA synthesis.
- Elongation: RNA polymerase adds nucleotides to the growing RNA strand.
- Termination: Transcription ends at the terminator sequence, and RNA is released.
What is the product of transcription, and how is it modified in eukaryotes?
• Product: Pre-mRNA.
• Modifications:
1. Addition of a 5’ cap.
2. Addition of a poly-A tail at the 3’ end.
3. Splicing to remove introns and join exons.
What is a mutation?
A change in the sequence of DNA nucleotides.
What is a point mutation?
A mutation involving a single nucleotide pair in DNA.
What are the three major types of point mutations?
Silent mutation- no changes in protein
Misense mutation- change in one amino acid
Nonsense mutation- introduce a stop codon, prematurely ending protein synthesis
Why can the effects of a base pair substitution vary?
• Some substitutions cause silent mutations with no effect.
• Others result in missense mutations (changing the amino acid) or nonsense mutations (introducing a stop codon).
How can a base pair substitution reduce or increase the size of a polypeptide?
• Reduce size: By introducing a premature stop codon (nonsense mutation).
• Increase size: If it alters a stop codon, causing translation to continue.
What causes a frameshift mutation, and why are its effects serious?
• Cause: Insertion or deletion of nucleotides not in multiples of three.
• Effect: Alters the reading frame, disrupting all downstream codons.
What is a mutagen?
A physical or chemical agent that increases the rate of DNA mutations.
What do X-rays and UV light do to DNA?
• X-rays: Cause breaks in the DNA backbone.
• UV light: Induces thymine dimers, disrupting base pairing.
What are base analogs, and how can they cause mutations?
Molecules
Cause: mispairing wrong base, incorporating DNA in wrong place, inserting incorrect nucleotides in replication
Why does protein synthesis occur more quickly in prokaryotes than in eukaryotes?
Transcription and translation occur simultaneously in prokaryotes, while in eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm.
What is the traditional view of how DNA controls a cell or organism?
DNA → RNA → Polypeptide → Protein → Cell structure and function → Organism’s anatomy and physiology (genotype determines phenotype).
