Chapter 16 (Exam 2: Chap. 13-21)

Question 1

Frederick Griffith (main idea)

Answer 1

used strep bacteria
o Two strands: 1 disease-causing (pathogenic) and 1 harmless (nonpathogenic)
o When he killed pathogenic bacteria with heat and mixed killed bacteria with live unpathogenic bacteria, living cells became pathogenic (harmful)
o All descendants had the trait of pathogenicity

Question 2

transformation

Answer 2

change in genotype and phenotype due to assimilation of external DNA by a cell

Question 3

bacteriophage

Answer 3

viruses that infect bacteria

Question 4

viruses

Answer 4

DNA enclosed by a protective coat

o Often just a protein

Question 5

Hershey Chase Exp- main idea

Answer 5

o ***Proved that nucleic acids (not proteins) are hereditary materials for certain viruses
o The DNA injected in the phage, not protein is what carries the genetic information that makes the cells produce the viral DNA and protein.

Question 6

Rosalind Franklin discoveries

Answer 6

• DNA is helical in shape and consists of 2 strands (double helix)
• Confirmed width of helix and spacing of nitrogenous bases
• Helix makes a full turn every 3.4 nm
• Bases are stacked .34 nm apart
• 10 layers of base pairs (20 rungs on ladder) for each full turn of helix

Question 7

antiparallel

Answer 7

subunits run in opposite directions

Question 8

semiconservative model

Answer 8

when a cell copies a DNA molecule, each strand serves as a template for ordering nucleotides into a new, complementary strand
o Result is 2 double-stranded DNA molecule
o 2 parental strands come together at the end of the process
o Predicted by Watson & Crick’s model
o **THE ACCURATE MODEL

Question 9

conservative model of DNA

Answer 9

2 parental strands reassociate after acting as templates for new strands

Question 10

dispersive model of DNA

Answer 10

Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

Question 11

origin of replication

Answer 11

• short stretches of nucleotides that have a specific sequence of nucleotides
o where replication begins

Question 12

Bacterial chrom. vs. Eukaryotic: how many origins of replication?

Answer 12

o Eukaryotic chromosomes have thousands of origins of replication; whereas bacterial chrom. has 1

Question 13

replication fork

Answer 13

Y-shaped region at the end of a replication bubble where parental DNA strands are unwound

Question 14

helicase

Answer 14

o Enzymes that untwist the double helix and replication forks
o Separate 2 parental strands, making them available as template strands

Question 15

Single-strand binding proteins

Answer 15

bind to unpaired DNA strands, keeping them from re-pairing

Question 16

topoisomerase

Answer 16

relieves the strain caused by the untwisting of the double helix by breaking, swiveling, and joining DNA strands

Question 17

primer

Answer 17

initial nucleotide chain produced during DNA synthesis

o Is actually a short stretch of RNA

Question 18

primase (7 functions)

Answer 18

enzyme which synthesizes the primer
o Slows down the progress of the replication fork
o Coordinates the placement of primers and the rates of replication on the leading and lagging strands
o Synthesizes the RNA primer at 5’ end of leading strand and 5’ end of each Okazaki fragment of lagging strand (bacterial DNA)

Question 19

DNA polymerase

Answer 19

catalyzes the synthesis of new DNA by adding nucleotides to a preexisting chain
o There exist about 11 different DNA polymerases in humans
o Require a primer and a DNA template strand
o Proofread nucleotide against its template. Removes nucleotide if it is incorrect.

Question 20

DNA polymerase I

Answer 20

• Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides`

Question 21

DNA polymerase III

Answer 21

• Remains in the replication fork on the template strand and constantly adds nucleotides
• Uses parental DNA as a template to synthesize new DNA by adding nucleotides to an RNA primer or pre-existing DNA strand

Question 22

Leading strand

Answer 22

o When a complementary strand is synthesized continuously in the 5’→3’ direction
o DNA polymerase III stays in the replication fork on the template strand and constantly adds nucleotides

Question 23

Lagging strand

Answer 23

o When DNA polymerase III works on template strand in direction AWAY from the replication fork
o Synthesized discontinuously with Okazaki fragments

Question 24

Okazaki fragments

Answer 24

segments of lagging strand which are synthesized discontinuously
• Formed by DNA polymerase III
• Each fragment must be primed separately

Question 25

DNA ligase

Answer 25

o On leading strand: joins 3’ end of DNA (which replaces primer) to rest of leading strand of DNA
o On lagging strand: joins Okazaki fragments
o Joins the final nucleotide of the replacement DNA segment to the first DNA nucleotide of the adjacent Okazaki fragment

Question 26

mismatch pair

Answer 26

enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors

Question 27

nuclease

Answer 27

Enzyme which cuts out damaged DNA
o Resulting gap is filled in with nucleotides (using undamaged strand as a template)
o Nucleotide excision repair

Question 28

Nucleotide excision repair

Answer 28

when a DNA polymerase and DNA ligase are responsible for filling in the gap

Question 29

telomeres

Answer 29

o Special nucleotide sequences which prevent the staggered ends of the daughter molecule from activating the cell’s systems for monitoring DNA damage (when cell detects DNA damage, signal transduction pathways can lead to cell death)
o Acts as a buffer zone providing protection against gene’s shortening
o Do not contain genes
o Consists of multiple repetitions of a short nucleotide sequence
o Get shorter and shorter with each round of replication

Question 30

telomerase

Answer 30

catalyzes the lengthening of telomeres in eukaryotic germ cells
• Compensates for shortening that occurs during replication
• Abnormally high in somatic cancer cells
• Common in germ cells

Question 31

chromatin

Answer 31

DNA and protein
o Found in nucleus
o Multilevel system of packing

Question 32

Levels of packaging (increasing in size)

Answer 32

DNA (double helix)–> Histones–> Nucleosomes–> 30-nm fiber–>Looped domains–> Metaphase chromosomes

Question 33

DNA (double helix)

Answer 33

• Ribbonlike part of DNA represents a sugar-phosphate backbone

Question 34

Histones

Answer 34

• proteins responsible for first level of DNA packing in chromatin
• Each contains ~100 amino acids
• Four common types: H2A, H2B, H3, H4

Question 35

Nucleosome

Answer 35

• (10 nm fiber) unfolded chromatin
• 10 nm in diameter
• Resembles beads on a string
• Linker DNA: Is the ‘string’ between the ‘beads’
• Consists of DNA wound around a protein consisting of 8 histones
• Histone types involved: H2A, H2B, H3, H4

Question 36

30-nm fiber

Answer 36

• results from interactions b/t histone tails on a nucleosome and linker DNA and nucleosomes
• Histone types involved: H2A, H2B, H3, H4

Question 37

looped domains

Answer 37

loops formed by 30-nm fiber which are attached to a chromosome scaffold composed of proteins
• Is a 300-nm fiber
• Rich in topoisomerase and H1 molecules

Question 38

metaphase chromosome

Answer 38

looped domains are coiled and folded
• Width is 700 nm
• Packing steps are specific and precise

Question 39

heterochromatin

Answer 39

interphase chromatin
o Visible as irregular clumps with a light microscope
o Inaccessible to parts of cell responsible for transcribing genetic info in DNA

Question 40

euchromatin

Answer 40

less compacted chromatin

o Loose packing makes DNA accessible to machinery responsible for transcribing the genetic info found in DNA