Translation Flashcards
(20 cards)
Compare and contrast translation in prokaryotes and eukaryotes
Prokaryotes: No nucleus, translation begins during transcription, uses Shine-Dalgarno for ribosome binding, and starts with fMet, polycistronic
Eukaryotes: Translation occurs after transcription in cytoplasm, ribosome binds the 5′ cap, starts with Met, monocistronic
Describe the function of the ribosome
They are responsible for synthesizing proteins
by reading messenger RNA (mRNA) to determine the sequence of amino acids, which then form a protein.
Describe the structure of the ribosome
A ribosome is made of RNA and proteins. Each ribosome consists of two separate RNA-protein complexes, known as the small and large subunits. The large subunit sits on top of the small subunit, with an RNA template sandwiched between the two.
Explain the major events that occur during initiation, elongation, and termination of translation
- Initiation involves bringing together the ribosome, mRNA, and the first tRNA.
- Elongation is the process of adding amino acids to the growing polypeptide chain
- Termination occurs when a stop codon is encountered, signaling the release of the completed protein.
What is a codon?
a sequence of 3 nucleotides
What is an anticodon?
a three-nucleotide sequence on transfer RNA (tRNA) that binds to the complementary codon on the mRNA
What is a reading frame?
The way a sequence of nucleotides in mRNA is divided into codons
What is an open reading frame?
a sequence of nucleotides that can be translated into a protein, starting with a start codon and ending with a stop codon
What is the role of the tRNA in the process of translation?
They act as a bridge between mRNA and the ribosome, ensuring accurate translation of the genetic code
(Match an mRNA codon with the amino acid it codes for)
How can mutations affect protein evolution?
They introduce genetic variation that can lead to changes in protein structure, function, and expression, potentially leading to new variations in a population
What is a point mutation?
a change in a single nucleotide base within a DNA sequence:
- substitution
- insertion
- deletion
What is a silent mutation? What effect does it have on the resulting protein?
a change in the DNA sequence that doesn’t alter the resulting amino acid sequence of the protein
What is a missense mutation? What effect does it have on the resulting protein?
a type of point mutation where a single nucleotide change in a DNA sequence results in a different amino acid being incorporated into a protein
What is a nonsense mutation? What effect does it have on the resulting protein?
a genetic change that alters a DNA sequence, causing a premature stop codon (also called a nonsense codon) to appear during protein synthesis
What is a frameshift mutation? What effect does it have on the resulting protein?
a genetic alteration that changes the reading frame of a DNA or RNA sequence
(note: inframe shift if it’s multiples of 3)
How can you predict the anticodon given the mRNA sequence or amino acid associated with the anti codon?
From mRNA: Use base pairing (A–U, G–C) in reverse orientation.
Example: mRNA codon AUG → anticodon 5′-CAU-3′
From amino acid: Use the genetic code to find the codon(s), then write the complement of the codon as the anticodon, in 5′ to 3′ direction.
How can you predict how changing tRNAs or other components of the translation machinery could alter the process and products of translation
tRNA changes:
- Abundance: Alters speed, stalling, or frameshifting.
- Anticodon: Redirects decoding (e.g., nonsense suppression, codon reassignment).
- Modifications: Affects accuracy/wobble.
Ribosomes:
- Mutations increase errors, frameshifting, or enable novel functions.
How do DNA/RNA changes show up on protein gels?
- No band → Gene deleted or mRNA destroyed
- New band → Gene added or mRNA stabilized
- Bigger band → Extra parts added or stop codon ignored
- Smaller band → Protein cut short or mRNA broken
- Darker band → More gene copies or stronger mRNA
- Lighter band → Gene silenced or mRNA blocked
Remember:
- No protein = problem in DNA/RNA
- Wrong size = DNA changed or mRNA edited
- More/less protein = DNA/RNA amount changed
Relate the length of a gene to its primary and mature mRNA
Primary mRNA (pre-mRNA):
- Length ≈ gene length (includes introns + exons)
- Longer than mature mRNA
Mature mRNA:
- Length ≈ only exons (after splicing)
- Shorter than gene due to: Intron removal, 5’ cap addition, 3’ poly-A tail
Relate the number of nucleotides in an open reading frame to the number of amino acids in a protein produced from it
- ORF length (nucleotides) ÷ 3 = # of amino acids
(Each codon = 3 nucleotides → 1 amino acid)
- Subtract 1 for the stop codon (if present)
