Molecular Basis of the Gene

Question 1

Transformation

Answer 1

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

Think: Griffith and Avery

Griffith did not know in 1928 what the transforming factor was made of!

Avery and team figured it out.

Question 2

phage

Answer 2

Virus that attacks bacteria

Question 3

Chargaff’s rules

Answer 3

DNA base composition varies between species

For each species. the % of A and T are roughly equal

The % of G and C bases are roughly equal.

Question 4

photo 51

Answer 4

Confirmed DNA is a helix

2 strands (not 3)

uniform width (eliminating Watson’s idea that A could pair with A)

Question 5

Antiparallel

Answer 5

subunits run in opposite directions

5’ to 3’ paired to a strand that is running 3’ to 5’

The 5’ end has a phosphate group, the 3’ a -OH

Question 6

semiconservative model of replication

Answer 6

Proposed by Watson and Crick, proven by Meselson and Stahl.

Question 7

origins of replication

Answer 7

sites where DNA replication begins

Question 8

Replication fork

Answer 8

Y shaped region where the parental strands are being unwound by helicase (shown in yello)

Question 9

single-strand binding proteins

Answer 9

bind to unpaired DNA strands to keep them from re-pairing

Question 10

topoisomerase or gyrase

Answer 10

The untwisting of the DNA causes strain ahead of the fork.

Topoisomerase relieves the strain.

Question 11

primer

Answer 11

short stretch of RNA (5 to 10 nucleotides long)

Made by primase.

The primer is shown in green.

Question 12

DNA polymerase

Answer 12

catalyze the synthesis of new DNA by adding nucleotides to the 3’ end of the preexisting chain.

There are several polymerases in E.Coli but 2 you need to know.

DNA polymerase I and DNA polymerase III

There are 11 in eukaryotes!

DNA polymerase can add 500 nucleotides per second in prokaryotes and 50 per second in human cells.

Question 13

leading strand vs. lagging strand

Answer 13

leading: one primer, made continuously by DNA pol III
lagging: many primers, made discontinuously, series of segments called Okasaki fragments.

Fragments are 1000-2000 nucleotides in E. coli and 100-200 nucleotides in Eukaryotes

Question 14

ligase

Answer 14

enzymes the joins the sugar-phosphate backbones of the Okasaki Fragments

We’ll see it again in figure 13.21 and 13.25

Anytime repairs must be made, ligase is used!

Question 15

mismatch repair/change in base repair

Answer 15

Even though DNA polymerase is a great proofreader (there is one error per 10 billion nucleotides) it does happen.

Other enzymes remove (nuclease) and replace incorrectly paired nucleotides.

Ligase seals the backbone together.

One mismatch is associated with a form of colon cancer.

Question 16

telomeres

Answer 16

As a result of many rounds of replication, DNA molecules get shorter.

telomeres protect the ends of DNA-contain no genes.

A buffer zone of repeated TTAGGG to protect genes.

Postpone erosion of genes

The telomerase enzyme lengthens telomeres but is not active in most human cells.

The shortening of telomeres is proposed to play a role in aging.

Short Video: https://www.youtube.com/watch?v=U0fRAr-ZHCo

https://www.healthline.com/health/telomeres#telomere-lengthening

Question 17

purine

Answer 17

2 ring nitrogenous base

Includes A and G

Question 18

pyrimidine

Answer 18

one ring nitrogenous base

includes cytosine, thymine and uracil

Question 19

hydrogen bonds

Answer 19

hold DNA together

3 for G and C

2 for A and T

Question 20

covalent bond

Answer 20

holds:

sugar to phosphate

sugar to nitrogenous base

Question 21

semiconservative replication

Answer 21

one old strand and one new strand.

Meselson-Stahl

Question 22

replication fork

Answer 22

Y shaped region where the parental strands are being unwound

Question 23

primer

Answer 23

short strand of RNA made by primase

5-10 nucleotides long

uses parental strand

Question 24

leading vs. lagging strand

Answer 24

Leading:DNA polymerase continuously adds nucleotides to the new strand as fork progresses.

Lagging: discontinuous, moving away from the fork, series of segments called Okasaki fragments

Question 25

DNA ligase

Answer 25

The enzyme that glues the fragments into a continuous step.

Can glue a plasmid together or when a repair is made to the DNA

Question 26

nuclease

Answer 26

DNA cutting enzyme.

Removes damaged DNA

Question 27

telomerase

Answer 27

an enzyme that elongates telomeres

active in germ cells, not somatic cells

may be overacitve in cancer cells

Question 28

histone

Answer 28

100 amino acids

first level DNA packing

Four types of histones

Question 29

nucleosome

Answer 29

DNA wound twice around a protein core of 8 histones

Question 30

genetic engineering

Answer 30

direct manipulation of genes for practical purposes

agriculture

criminal law

medical research

Question 31

plasmid

Answer 31

a circular molecule of DNA

Question 32

recombinant DNA

Answer 32

a molecule of DNA containing two different sources often different species

Question 33

restriction enzymes

Answer 33

cut up DNA at a specific site, called a restriction site

Question 34

sticky ends vs. blunt ends

Answer 34

unpaired bases

Question 35

PCR

Answer 35

polymerase chain reaction

This technique can make billions of copies of a specific target DNA

Question 36

CRISPR Cas 9

Answer 36

bacterial protein that helps defend bacteriophage infections.

Cas9 works with guide RNA (homing device)

Cas9 cuts specific DNA.

Triggers DNA repair or the DNA can be knocked out