Lecture 2: DNA Synthesis and Replication

Question 1

“Beads on a String”

Answer 1

DNA tightly wound to histones. Must be unwound to this form to be usable for DNA replication.

Question 2

Histones

Answer 2

Positively charged protein in chromatin used for condensing DNA.

Question 3

Nucleosomes

Answer 3

Protect DNA from degradation. Made up of 8 histones (80bp between each histone).

Question 4

Histone Acetylation

Answer 4

Acetylated histones- Have a neutral charge that does not interact with DNA. DNA is more unwound (less condensed) and able to have more gene expression.
Unacetylated histones- Have a positive charge and keep DNA condensed and tightly wound.

Question 5

Origin Recognition Complex

Answer 5

Multi-subunit complex that binds to origin site and regulates the start of replication. This occurs during S phase.

Question 6

Epigenetic Inheritance

Answer 6

Heritable traits that occur without changes to DNA sequence. i.e. Methylation of histones is inherited and is not in the genome.

Question 7

Replication

Answer 7

Process by which DNA creates an exact copy of itself.

Question 8

DNA Polymerase

Answer 8

Enzyme that copies template strand and adds complimentary base pairs on new strand. Synthesizes in 5’ to 3’ direction. Also has proofreading mechanisms to ensure correct base pairing.

Question 9

Okazaki Fragments

Answer 9

Small fragments synthesized from the 5’ to 3’ direction on lagging strand. Fragments joined together by DNA Ligase.

Question 10

Leading Strand

Answer 10

5’ to 3’ direction and is synthesized continuously by the DNA Polymerase.

Question 11

Lagging Strand

Answer 11

3’ to 5’ direction and is made up of Okazaki Fragments. DNA Polymerase uses an RNA Primer

Question 12

RNA Primer

Answer 12

Created by DNA Polymerase and Primase. Adds a short strand of RNA for starting point of DNA synthesis. Necessary for DNA polymerase to function (especially on lagging strand).

Question 13

Primase

Answer 13

Builds RNA primers

Question 14

DNA Ligase

Answer 14

Joins together Okazaki fragment and exons. Acts as a “glue”.

Question 15

DNA Helicase

Answer 15

Unzips double-stranded DNA at origin site to begin replication. Uses ATP as motor to slide along DNA.

Question 16

Single-strand DNA Binding Proteins

Answer 16

Aid helicase in unwinding DNA. They bind to single-stranded DNA and help to prevent the DNA from creating hairpin loops.

Question 17

Sliding Clamp

Answer 17

Keeps DNA Polymerase bound to strand of DNA during replication. Without it the polymerase would detach too early.

Question 18

Clamp Loader

Answer 18

Loads a sliding clamp to each primer to aid DNA Polymerase.

Question 19

Telomere

Answer 19

End of linear chromosomes that are composed of tandem repeats. Telomere length is maintained in germ cells by telomerase, but in somatic cells telomeres are shortened and can lead to cell senescence(cell stops dividing) or apoptosis.

Question 20

Telomerase

Answer 20

Recognizes end of telomere and elongates it in 5’ to 3’ direction. Places a primer on lagging strand as well to extend it.

Question 21

Reverse Transcriptase

Answer 21

Synthesizes DNA from RNA. Telomerase has the ability to do this.

Question 22

Telomerase

Answer 22

Recognizes end of telomere and elongates it in 5’ to 3’ direction. Places a primer on lagging strand as well to extend it. In cancer cells, cells express high levels of telomerase which make them immortal. In Progeria, cells do not express telomerase and cells senesce quickly.

Question 23

Reverse Transcriptase

Answer 23

Synthesizes DNA from RNA. Telomerase has the ability to do this.

Question 24

Topoisomerase

Answer 24

Relieve torsional stress in unwound DNA and prevents super coiling

Question 25

Cell Senescence

Answer 25

Cell stops dividing. (Cause of aging)

Question 26

Bloom’s Syndrome

Answer 26

BLM protein is defective and helicase does not work properly. DNA cannot unwind or be repaired. Leads to developmental delays, high risk of cancer, and causes premature aging.

Question 27

Heterochromatin

Answer 27

Highly condensed DNA and genes are silenced (not expressed). This occurs near the nuclear periphery.

Question 28

Euchromatin

Answer 28

Highly expressed regions of DNA not wound tightly. Found in central core of nucleus and is easily accessible for replication.