Exam #4: Structure & Organization of Nucleic Acids

Question 1

What is non-coding DNA?

Answer 1

Non-protein coding sequences

Question 2

List four types of non-coding DNA

Answer 2

1) Spacer Sequences
2) Introns
3) Genes encoding nonprotein-coding RNA
4) Repetitious DNA (most abundant)

Question 3

Exon

Answer 3

Sequence of DNA translated into protein

Question 4

Intron

Answer 4

Sequences of DNA that are spliced out

Question 5

Gene Family

Answer 5

Genes that have a similar nucleotide sequence & encode similar proteins

Question 6

Pseudogenes

Answer 6

Mutation of a gene gives rise to an inactive duplicate

Question 7

How do gene families arise?

Answer 7

Spontaneous mutation and meiotic accidents

Question 8

What is chromatin?

Answer 8

Complex of DNA and protein

Question 9

How many chromosomes are found in a diploid human cell?

Answer 9

46: 2 sex chromosomes & 44 autosomes

Question 10

How is the mitochondrial genome different from the nuclear genome?

Answer 10

• Circular molecule
• Present in multiple copies per organelle
• encodes 13 proteins & 24 RNA molecules
• Not extensively associated with proteins

Question 11

Heterochromatin

Answer 11

• Stained
• Complex with proteins
• Transcriptionally inactive
• Periphery

Question 12

Euchromatin

Answer 12

• Translucent
• Transcriptionally active
• Decondensed

Question 13

What processes occur in the nucleolus?

Answer 13

Assembly of ribosomal subunits

Question 14

Key features of the nuclear pore complex

Answer 14

• Nuclear basket on the nuclear side
• Protein ring anchored to the double membrane
• Central transporter inside protein ring
• Filaments on cytoplasmic side

Question 15

Ran-dependent import into the nucleus

Answer 15

Ran & Importin = Protein & Ribosomal subunits into the nucleus

1) Importin + Cargo enters nucleus
2) Importin/Cargo + Ran-GTP= Cargo released
3) Ran-GTP/Importin= Exported to Cytoplasm
4) GTP hydrolyzed= Ran-GDP + Importin dissociate
5) Ran-GDP re-enters nucleus

Question 16

Ran-dependent export from the nucleus

Answer 16

Ran & Exportin = protein out of the nucleus

1) Cargo + Exportin
2) Cargo/Exportin + Ran-GTP= Exported
3) GTP hydrolyzed= Dissociation in cytoplasm
4) Ran-GDP & Exportin re-enter nucleus

Question 17

Semi-conservative Replication

Answer 17

• Each strand of parental DNA serves as a template for synthesis of a new complimentary DNA strand
• Each daughter DNA contains 1 parental strand and 1 newly synthesized strand

Question 18

Replication Origin

Answer 18

Where replication begins; multiple origins on each chromosome

Question 19

Bidirectional Replication

Answer 19

Replication is bidirectional from each origin

Question 20

What are the nucleotide donors for DNA synthesis?

Answer 20

dATP, dGTP, dCTP, and dTTP

Question 21

What is the significance of the pyrophosphate formed during chain elongation?

Answer 21

• Pyrophosphate is released as each nucleotide is incorporated into DNA
• Hydrolysis of pyrophosphate drives the reaction to the right

Question 22

Key features shared by DNA polymerase

Answer 22

Note, y-DNA polymerase synthesizes mitochondrial DNA

1) Template-directed
2) Primer is required
3) Synthesize 5’–>3’
4) Newly synthesized DNA is anti-parallel to template

Question 23

DNA Helicase

Answer 23

Use ATP-energy to unwind DNA double helix for replication

Question 24

Single stranded DNA binding proteins

Answer 24

bind unwound DNA to prevent re-association

Question 25

Topoisomerase

Answer 25

Relieve the supercoiling created by undwinding by nicking and religating DNA

Question 26

RNA primer

Answer 26

Required for DNA synthesis; synthesized by DNA polymerase alpha

Question 27

Leading Strand

Answer 27

Primer points toward the replication fork and synthesizes continuously

Question 28

Lagging Strand

Answer 28

Primer points away from the replication fork and is synthesized in fragments

Question 29

Okazaki Fragment

Answer 29

Fragments of DNA synthesized on lagging strand

Question 30

Telomeres

Answer 30

End of chromosome with special TTAGGG sequence repeats

Question 31

How are telomeres replicated?

Answer 31

Enzyme Telomerase that contains RNA molecule complimentary to telomere that acts as a template for extension of the 3’ end of DNA

Question 32

Satellite DNA

Answer 32

Simple-sequence DNA i.e. identical repeats of short DNA sequences confined to the centromere & telomere

Question 33

Example of a gene family

Answer 33

B-globin has 5 genes clustered together on chromosome 11: 2x adult globins, 2x fetal globins, and 1x embryonic globin

Question 34

3 Levels of DNA Condensation

Answer 34

1) DNA wrapped around histones to form nucleosome
2) Nucleosomes associated to form 30nm solenoid fiber
3) 30nm solenoid fibers form 300nm loop domains

Question 35

What organelle separates transcription and translation?

Answer 35

Nucleus

Question 36

What does the separation of transcription from translation allow?

Answer 36

Post-transcriptional modification of RNA

Question 37

mRNA Export from Nucleus

Answer 37

Ran-Independent

Question 38

ORC

Answer 38

Origin of Replication Complex: protein that marks origin of replication

Question 39

Primase

Answer 39

DNA Polymerase alpha

Question 40

DNA Ligase

Answer 40

joins Okazaki fragments

Question 41

DNA polymerase gamma

Answer 41

Elongates DNA

Question 42

Topoisomerase Inhibitors

Answer 42

• Topoisomerase: Relieves supercoiling during replcation

- Drugs can inhibit this process and work as anti-cancer drugs or antibiotics

Question 43

Doxorubicin

Answer 43

Human Topoisomerase inhibitor used in cancer chemotherapy

Question 44

Nalidixic Acid & Ciprofloxacin

Answer 44

Bacterial topoisomerase inhibitors that work as anti-biotics