Bio 112 Final exam

A bacterium infected with a phage made of a T2 protein coat and T4 DNA will produce ________.

T4 phages

Viruses use host cells to make ________.

Viral nucleic acids and viral proteins

Hershey & Chase used the fact that DNA contains ________ and protein contains ________.

Phosphorus; sulfur

During the experiment, the T2 phage ________.

Injected its DNA into the host cell

 If G = 19%, thymine = ________.

31%

Most current definition of a gene:

A DNA sequence that codes for a functional product (protein or RNA)

Base-pairing combinations consistent with rules:

A = T and G = C

 The phosphodiester bond forms between the phosphate of the new nucleotide and the ________ of the previous one.

3' hydroxyl (–OH)

A–T and C–G pairing ensures ________.

Uniform width of the DNA helix

If DNA strands were joined by covalent bonds:

They could not separate for replication or transcription.

Semiconservative model supported by ________.

Meselson and Stahl

Template in semiconservative replication:

 Each parent strand

DNA is synthesized by ________.

Semiconservative replication

 Correct order of replication steps:

 Helicase → Primase → DNA polymerase → Ligase

Enzyme that catalyzes phosphodiester bonds:

DNA polymerase

Energy for DNA synthesis comes from ________.

dNTPs (nucleotide triphosphates)

Major difference between eukaryotic and prokaryotic replication:

Eukaryotes have many origins of replication; prokaryotes have one

 ________ unwinds DNA; ________ relieves tension.

 Helicase; Topoisomerase

 DNA polymerase III in E. coli:

Main enzyme that adds nucleotides

Leading vs. lagging strand:

Polymerase can only synthesize 5' → 3'

DNA ligase role:

Connects Okazaki fragments

Proteins that keep DNA strands separated:

 Single-strand binding proteins (SSBs)

 Telomeres replicate differently because ________.

Lagging strand cannot fully replicate the ends

Telomere conservation reflects ________.

Their essential protective function

A telomere is ________.

A repetitive DNA sequence protecting chromosome ends

Lowest telomerase activity occurs in ________ cells.

Somatic cells

Telomere shortening is a problem in ________.

Frequently dividing cells

Gene expression is ________.

Using DNA to make RNA and proteins

One-Gene, One-Polypeptide Hypothesis:

Each gene encodes one polypeptide

Scientists who proposed it:

Beadle and Tatum

Knockout mice have genes ________.

 Inactivated (knocked out)

“DNA → RNA → Protein” is the ________.

 Central dogma

Not synthesized from DNA:

Amino acids

Transcription synthesizes ________.

RNA

In eukaryotes, transcription is in the ________ and translation in the ________.

Nucleus; cytoplasm

Retrovirus enzyme that makes DNA from RNA:

Reverse transcriptase

________ is to transcription as ________ is to translation.

RNA polymerase; ribosome

DNA: TTTTTTT → RNA: ________

AAAAAAA, synthesized in the nucleus

mRNA from 3’ ATG GGC AAT CGC 5’:

5’ UAC CCG UUA GCG 3’

Start codon:

AUG

Stop codons:

UAA, UAG, UGA

Genetic code is unambiguous because ________.

Each codon = 1 amino acid

Genetic code is redundant because ________.

Multiple codons for same amino acid

Bases needed per amino acid:

Three

Code is nearly universal because ________.

Most organisms use the same codons

Two-base codons would allow ________ amino acids.

16

Sickle-cell mutation type:

Missense mutation

Premature stop codon mutation:

Nonsense mutation

Silent mutation:

Base change with no amino acid change

Frameshift mutations occur from ________.

insertion or deletion

Segment inserted into another chromosome:

Translocation

Segment reversed in the same chromosome:

inversion

Chromosome segment copied and added again:

duplication

Without ________, RNA polymerase cannot start transcription at the correct sites.

Sigma factor

To express a eukaryotic gene in bacteria, you must include ________.

A bacterial promoter

 Central to bacterial transcription initiation:

The promoter

Termination occurs when ________.

RNA polymerase reaches a termination sequence

After transcription begins, sigma ________.

Detaches from RNA polymerase

Occurs in prokaryotes but not eukaryotes:

Coupled transcription and translation

Ribosomes can bind prokaryotic mRNA ________.

 Before transcription is complete

Primary purpose of RNA splicing:

Remove introns and join exons

Introns are ________.

 Non-coding sequences removed from pre-mRNA

Adapter molecule in translation:

tRNA

 61 codons, 45 tRNAs explained by ________.

wobble pairing

Anticodon of tRNA is ________.

 Complementary to the mRNA codon

Ribosome binding site in prokaryotes:

Shine–Dalgarno sequence

Site where codon is read:

A site

 After peptide bond forms:

Ribosome shifts; tRNA moves A → P

 Missing ________ prevents translation initiation in eukaryotes.

5’ cap

Translation requires ________.

mRNA, ribosomes, tRNA, amino acids, and energy (GTP)