CHAPTER 13 Flashcards
(32 cards)
What is the main function of genetic material in cells?
-Encode the production of cellular proteins in the correct cell, at the proper time, and in the correct amount.
What disease did Archibald Garrod study, and what did he propose about it?
He studied alkaptonuria, proposing it was due to a missing enzyme (homogentisic acid oxidase) and that the disease followed a recessive pattern of inheritance.
What hypothesis did Beadle and Tatum’s work with Neurospora crassa lead to?
The “one gene–one enzyme” hypothesis, suggesting each gene controls the synthesis of a single enzyme.
How was the one gene–one enzyme hypothesis modified?
It was refined to “one gene–one polypeptide,” acknowledging that genes also code for non-enzyme proteins and functional RNAs.
Codon
A group of three nucleotides on mRNA that specifies an amino acid.
Which codon is the start codon, and what does it specify?
AUG is the start codon, specifying methionine and setting the reading frame.
What does it mean that the genetic code is degenerate?
Multiple codons can specify the same amino acid, called synonymous codons.
Which amino acids are more likely to be found on the surface of proteins?
Polar and charged amino acids, as they are hydrophilic.
Name the four levels of protein structure.
-Primary (sequence)
-Secondary (α-helix and β-sheet)
-Tertiary (3D folding)
-Quaternary (subunit association).
What are some functions of proteins in cells?
-Transport
-cell signaling
-cell shape
-enzyme activity
-cell surface recognition
What is the function of tRNA in protein synthesis?
It serves as an adaptor molecule, recognizing mRNA codons and carrying the corresponding amino acid.
What enzyme is responsible for attaching amino acids to tRNA?
Aminoacyl-tRNA synthetase, with one specific enzyme for each amino acid.
Why is accuracy in aminoacyl-tRNA synthetase important?
It ensures the correct amino acid is attached to tRNA, preventing nonfunctional polypeptides
Anticodon
A sequence on tRNA that pairs with a complementary codon on mRNA during translation.
What are selenocysteine and pyrrolysine?
Uncommon amino acids encoded by UGA and UAG codons, found in specialized enzymes.
The reading frame begins with a ____________ and is read _____________.
Start codon; in groups of three bases.
Wobble Rule
Explains that the first two positions in codon-anticodon pairing follow strict AU/GC rules, but the third position can “wobble,” allowing for some mismatches.
What are isoacceptor tRNAs?
Isoacceptor tRNAs are tRNAs that can recognize the same codon but differ at the wobble position.
If a tRNA has the anticodon sequence 3’—GAC—5’, which amino acid does it carry?
Leucine
Aminoacyl-tRNA synthetase
Enzyme attaches an amino acid to the 3’ end of a tRNA
What are the two types of ribosomes in eukaryotic cells?
- Cytoplasmic ribosomes
- ribosomes found in organelles (mitochondria and chloroplasts).
What are the three functional sites of a ribosome?
- Peptidyl site (P site)
- Aminoacyl site (A site)
- Exit site (E site)
What stages make up the translation process?
- Initiation
- Elongation
- Termination
What is the Shine-Dalgarno sequence, and where is it found?
The Shine-Dalgarno sequence is a ribosomal binding site in bacteria that helps align the mRNA with the 30S subunit.
