Genetics chapter 18 question

start codon

AUG

Negatively charge amino group (acidic)

Aspartate (Asp) Glutamate (Glu)

Nonpolar, aliphatic amino group

Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) methionine (Met)

Positively charged amino group (basic)

Lysine (Lys) Arginine (Arg) Histidine (His)

difference between translation in bacteria vs eukaryotes

Mehionine of initiator tRNA is formylated ribosome binding site on mRNA has two parts (start codon and Shine dalgarno sequence)

Aromatic Amino group

Phenylalanine (Phe) Tyrosine (Tyr) Tryptophan (Trp)

Polar, uncharged amino group

Serine (ser) Threonine (Thr) Cysteine (cys) Proline (pro) Asparagine (Asn) Glutamine (Gln)

stop codons

UGA, UAA, UAG

what is the difference between a transition and a transversion? which type of base substitution is usually more common?

a transition is a mutation that changes a purine to a different purine (A-G) or a pyrimidine to a different pyrimidine (C-T) . A transversion changes a purine to a pyrimidine or vice versa (A/G-C/T) or vice versa. Transitions are much more common than transversions

A site

accepts charged tRNAs that have the correct anticodon

how do alkylating agents, nitrous acid, and hydroxylamine produce mutations?

alkylating agents donate methyl (or ethyl) to the bases. this results in mispairing and typically leads to transition mutations. Nitrous acid treatment results in the deamination of cytosine, producing uracil, which pairs with adenine. During the next round of replication, a CF to AT transition will occur. deamination of guanine will produce of CG to TA transition if bonded with Thymine. Hydroxylamine will produce CG to AT transitions when paired with Adenine.

role of small ribosomal subunit

binds to mRNA

aminoacyl-tRNA synthetases

catalyze addition of the correct amino acid to tRNAs

silent (synonymous) mutations

change in nucleotide sequence but no change in amino acid

synonymous codons

codons that specify the same amino acid

isoaccepting tRNAs

different tRNAs that accept the same amino acid but have different anticodons

briefly describe expanding nucleotide repeats. How do they account for the phenomenon of anticipation?

expanding nucletids repears occur when DNA insertion mutations result in an increase in the number of copies of a nucleotide repeat sequence. This may occur by errors in replication or unequal recombination.

What are two major mechanisms for the repair of double-strand breaks? how do they differ?

homologous recombination (requires identical DNA molecule) and nonhomologous end joining.

briefly describe two different ways in which intragenic suppressors can reverse the effects of mutation

intragenic suppression is the result of second mutations within an already mutated gene that restore a wild-type phenotype. The suppressor mutations are lovated at different sites within the gene from the orginical mutation. One type of suppressor mutation restores the original phenotype by reverting the meaning of a previously mutated codon to that of the original codon. The suppressor mutation occurs at a different position than the first mutation, which is still present within the codon. Intragenic suppression may also occur at two differnt locations within the same protein. If two regions of a protein interact, a mutation in one of these regions could disrupt that interaction. The suppressor mutation in the other region would restore the interaction. Finally, a freameshift mutation due to an insertion or deletion could be suppressed by a second insertion or deletion that restores the proper reading frame.

list at least three differeny types of DNA repair and briefly explain how each is carried out.

mismatch repair: replication errors that are the result of base-pair mismatch are repaired. mismatch-repair enzymes recognize problem, DNA pol fills the gap, DNA ligase seals it. Direct repair: DNA repair by directly changing damaged nucleotide to original structure Base-excision repair: removal of base, phosphodiester bond, and deoxyribose sugar.

What is the difference between a missense mutation and a nonsense mutation? between a silent mutation and a neutral mutation?

missense mutations change the sequence and meaning of an mRNA codon, resulting in a different amino acid. A nonsense mutation changes the codon to a stop codon. A silent mutation changes the sequence of a codon but not the meaning. A neutral mutation changes the sequence and meaning of a codon, but the different amino acid has little effect on protein function.

role of large ribosomal subunit

peptidyl transferase activity (peptide bond formation)

how do insertions and deletions arise?

strand slippage during replication and unequal crossover due to misalignment.

how do base analogs lead to mutations?

they have structures similar to nucleotides and can be incorporated into DNA during replication. They generally have a higher tendency of mispairing

E site

uncharged tRNA is released from this site

P site

where the amino acid is added to the polypeptide chain and transferred to the A site tRNA