quiz april 27th

What is the genetic material of all living organisms?

Deoxyribonucleic acid (DNA)

Before the 1940s, many biologists thought ___ was genetic material because it had 20 types of ___.

Protein; amino acids

What happens when living R strain bacteria are mixed with heat-killed S strain bacteria?

R strain transforms into S strain

What is the uptake of DNA from another cell that changes heredity called?

Transformation

What was Griffith’s transforming principle later identified as?

DNA

If protein were hereditary material, what would happen after protease treatment in Avery’s experiment?

The mice would live

Avery, MacLeod, and McCarty used enzymes to break down what molecules?

Protein, DNA, and RNA

Why were bacteria radioactive after infection with 32P-labeled viruses?

They incorporated 32P into DNA

Hershey and Chase concluded DNA enters bacteria because ___ was inside cells.

Radioactive DNA

T2 bacteriophages contain what molecules?

DNA and protein

In Hershey-Chase, 32P labeled ___ and 35S labeled ___.

DNA; protein

After two generations, integrated 32P-labeled DNA would be found in about what fraction of cells?

1/2

Watson, Crick, Franklin, and Wilkins are known for discovering what?

The 3D structure of DNA

Nucleic acids are long chains of what?

Nucleotides

Each DNA nucleotide contains what three parts?

5-carbon sugar, phosphate group, nitrogenous base

Adjacent nucleotides in DNA are linked by what bond?

Phosphodiester bond

If DNA is 47% G+C, then A+T equals what percent?

53%

If a genome has 14% guanine, what are thymine and cytosine percentages?

Thymine 36%, Cytosine 14%

If a genome has 30% adenine, what percent thymine is expected?

30%

Purines and pyrimidines are what type of molecules?

Nitrogenous bases

How do purines differ from pyrimidines?

Purines have 2 rings; pyrimidines have 1 ring

What are the purines in DNA?

Adenine and guanine

What are the pyrimidines in DNA?

Thymine and cytosine

Complementary strand to 5'-GACGTT-3'?

3'-CTGCAA-5'

Franklin and Wilkins used what technique to study DNA?

X-ray diffraction

What holds the two DNA strands together?

Hydrogen bonds

Is DNA helix width constant or variable?

Constant

What does antiparallel DNA mean?

One strand runs 5'→3', the other 3'→5'

The 5' end has a ___ group; the 3' end has a ___ group.

Phosphate; hydroxyl

How many hydrogen bonds connect A-T and G-C?

A-T = 2, G-C = 3

Why is DNA replication called semiconservative?

Each new DNA has one old strand and one new strand

After one generation in Meselson-Stahl, mixed DNA suggested replication was what?

Semiconservative or dispersive

Meselson-Stahl results ultimately supported what model?

One old strand + one new strand

DNA polymerase adds nucleotides to which end?

3' end

What does topoisomerase do?

Relieves twisting strain ahead of replication fork

DNA polymerase active sites are similar in what groups?

Archaea, bacteria, and eukaryotes

DNA ligase joins DNA fragments using what type of bond?

Covalent bond

What does helicase do?

Unwinds DNA double helix

Primase makes RNA primers to provide what for DNA elongation?

3' hydroxyl group

Why is ligase most active on lagging strand?

It joins many short DNA fragments

DNA synthesis always occurs in what direction?

5' → 3'

Okazaki fragments are found on which strand?

Lagging strand

Which strand is synthesized continuously in same direction as unwinding?

Leading strand

Eukaryotic chromosomes are ___ with ___ origins of replication.

Linear; multiple

Energy for new DNA bonds mainly comes from what?

Hydrolysis of pyrophosphate

If primase fails, what happens?

DNA unwinds but no new strands are made

Telomeres are found where?

Ends of chromosomes

What does human telomerase do?

Adds telomere repeats in some cells

Why are chromosome ends not fully copied?

RNA primers at ends cannot be replaced with DNA

Without telomerase in a clone, what happens eventually?

Cell division stops after many generations

Chromatin consists of what?

DNA and protein

What are nucleosomes?

Eukaryotic DNA associated with histones

Nucleosome core particle = ?

DNA wrapped around 8 histone proteins

During replication, nucleosomes must ___ then ___.

Disassemble; reassemble

During DNA replication, histones are also what?

Replicated

Prokaryotic chromosomes are ___ with ___ origin.

Circular; one

What enzyme proofreads replication errors?

DNA polymerase

Without proofreading, error rate is about 1 per how many nucleotides?

1,000 to 10,000

After repair enzymes remove wrong nucleotide, what finishes repair?

DNA polymerase and DNA ligase

Xeroderma pigmentosum causes high risk of what?

Skin cancer from sunlight

Most variability in offspring comes from what?

Mutations

If replication error is never corrected, after two divisions how many daughter cells have mutation?

Four

Cancer cells often maintain what enzyme?

Telomerase

What does the sliding clamp do?

Anchors DNA polymerase to template

Sliding clamp is highly conserved, meaning what?

Similar function across organisms

Increased exercise linked to longer telomeres may suggest increased what?

Telomerase activity

Cancer drugs may target rapidly dividing cells by doing what?

Inhibiting DNA replication or DNA repair enzymes