Bio Chap. 14 The Genetic Material

Front 1

Nucleotides
What are they?
3 components

Back 1

Monomers of the nucleic acids DNA and RNA

1) Nitrogenous base
2) Pentose sugar
3) Phosphate group

Front 2

How do DNA and RNA differ?

Back 2

DNA
• Has Thymine, but no uracil
• Pentose = deoxyribose

RNA
• Has Uracil, but no Thymine
• Pentose = ribose

Front 3

Pyrimidines vs. purines

Back 3

Pyrimidines
• smaller 6-membered ring
• Cytosine, Uracil, Thymine (CUT)

Purine
• larger 6-membered ring joined to a 5-membered ring
• Adenine, Guanine (AG)

Front 4

How do nitrogenous bases pair?

By what type of bond and how many?

Back 4

C-G = 3 hydrogen bonds

DNA:
• A-T = 2 hydrogen bonds

RNA:
• A-U = 1 hydrogen bond

Hydrogen bonding

Front 5

Do nucleotides have a positive or negative charge?
Acidic or basic?

Back 5

Negative and acidic due to phosphate group

Front 6

What type of bonds join nucleotides?

Back 6

Phosphodiester bonds

Front 7

What is the structure of a pentose? 1
What is it composed of and where are these components located? 6
What is the growing end and why? 3
By which process does it grow? 1
Draw it!

Back 7

Structure
• 5-membered ring

Composed of
• 1' C is at right, count clockwise
• 5' C branches off of 4' C
• 5th ring member is an O
• hydroxyl at 3'
• phosphate at 5'
• phosphodiester bonds between functional groups and C's

Growing end at 3'!!
• OH polarity = positive
• PO4 polarity = negative
• OH and PO4 are attracted to each other

Process
• Dehydration synthesis

Front 8

What about DNA was discovered through x-ray crystallography?
2

Back 8

1) X-ray beams were diffracted when they hit DNA molecules to show that DNA is a double helix

2) Base pairs discerned from % of each base in the genome seen from the x-ray

Front 9

The orientation of DNA's backbone and bases

Back 9

• Sugar-phosphate backbone is located on the outside towards the aqueous environment
• Nitrogenous bases located on the inside joining the 2 helixes by hydrogen bonds

Front 10

Antiparallel

Back 10

DNA strands are complementary to one another = they run parallel but reverse direction
5' - 3'
3' - 5'

Rather then:
5' - 3'
5' - 3'

Front 11

What are the 3 proposed models of DNA replication?
Which is correct?

Back 11

1) Conservative model = parental strands remain intact (conserved), and daughter strands are all new

2) Semiconservative model = parental strand is a template for replication; daughter contains 1 of the parental strands and 1 made from it

3) Dispersive model = daughter strands contains DNA of both parental and new daughter strand segments

Semiconservative is correct

Front 12

Mutations

What is involved in correcting them?

Back 12

Errors in base pairing during DNA replication/synthesis

Enzymes

Front 13

Bacterial DNA replication
2 sites of importance

Back 13

1) Ori = origin of replication

2) Termination sequences

These are sequences of DNA, not genes

Front 14

Replication bubbles

What would happen if there was just 1 replication bubble?

Back 14

• There are ori's running down the length of each DNA strand
• replication begins at each ori, forming bubbles at each site
• replication proceeds in opposite directions on each side of the bubble all adjacent bubbles meet and form 2 new strands
• If Eukaryote DNA had only 1 replication site the process would take too long; multiple bubble speed things up!

Front 15

To polymerize...

Back 15

is to grow through dehydration synthesis

Monomers → polymers

Front 16

DNA Polymerase III
What it does
By which process
What type of bond

Back 16

Polymerizes DNA by adding nucleotide monomers to the 3' end of a growing strand by dehydration synthesis
The strands are joined by phosphodiester bonds

Front 17

Where do the nucleotides that pair to the parental strand come from?

What are these nucleotides really?

Back 17

They are free nucleotides from the nucleoplasm

Nucleosides

Front 18

Nucleoside triphosphate

Back 18

The free DNA monomers that DNA poly III adds to the 3' end of the growing strand

Consists of:
• sugar
• nitrogenous base
• 3 phosphates

Front 19

Pyrophosphate

Back 19

2 phosphates that are removed from nucleoside triphosphate when nucleoside triphosphate bonds to the growing DNA strand

Front 20

What processes drives the growth of DNA strands?

Back 20

Exergonic removal of pyrophosphate from one nucleoside triphosphate drives endergonic bonding of another nucleoside triphosphate

Front 21

2 daughter strands

Difference in their construction

Back 21

Half of each daughter is a leading strand and half is a lagging strand

Leading strand = adds nucleosides as it proceeds away from ori, into the replication fork

Lagging strand = adds nucleosides as it proceeds towards ori, away from the fork

Leading strand is replicated continuously
Lagging strand is built in fragments

Front 22

Okazaki fragments

Back 22

Short DNA fragments that build the lagging strand

Front 23

Primers
How many are needed?

Primase

Why are they needed?

Back 23

Primers = Short RNA fragments which bond to the parental strand to act as a foundation for the daughter strand to be built upon

Primase = enzyme that joins primers to parental DNA strand
Leading strand needs 1 placed at ori
Lagging strand needs 1 per Okazaki fragment

DNA poly III can only add new DNA nucleotides to preexisting nucleotides

Front 24

DNA Polymerase I
DNA ligase

Back 24

DNA Polymerase I = enzyme that replaces RNA primer with DNA nucleotides

DNA ligase = once the primers are replaced with DNA, this enzyme joins Okazaki fragments at their sugar-phosphate backbones

Front 25

What are the mechanics of the lagging strand?
4

Back 25

1) An RNA primer is placed by primase behind the leading strand
2) An Okazaki fragment is laid down by DNA poly III in front of the primer (between primer and leading strand)
3) The primer is replaced with DNA nucleotides by DNA poly I
4) The Okazaki fragments are joined by DNA ligase

Front 26

Helicase

Back 26

Unwinds the double helix

Front 27

Single-strand binding proteins

Back 27

Prevents single DNA strands from breaking when they have been unwound from the helix

Front 28

Topoisomerase

Back 28

DNA de-tangler
Cuts, unwinds, and reattaches DNA strands at each replication fork

Think of teased hair - this prevents that