Chapter 5 CMB DNA Replication

Question 1

What is DNA?

Answer 1

• A double-stranded nucleic acid that contains the genetic information for cell growth, division and function.
• Made up of alphabets called bases (A,T,G,C*)
• These bases (arranged in triplets) code for amino acids which make up the proteins

Question 2

Where are chromosomes located?

Answer 2

Located in the nucleus of eukaryotic cells

Question 3

What are chromosomes composed of?

Answer 3

Composed of DNA wrapped around proteins called histones

Question 4

What are chromosomes?

Answer 4

Physical carriers of genes

Question 5

State the structural difference between chromatin and chromosome

Answer 5

Chromatin (decondensed or thread-like) vs chromosome (X-shaped: condensed chromatin)

Question 6

What is a chromatin?

Answer 6

A complex of DNA and proteins in the nucleus, that condense to form chromosomes, in eukaryotic cell division

Question 7

What are genes?

Answer 7

1. Genes are basic physical and functional units of heredity.
2. Genes are a set of instructions that determine what the organism is like, its appearance, how it survives, and how it behaves in its environment.
3. Genes codes for a protein
4. Genes codes for genetic traits that are inheritable

Question 8

Are DNA and Genes same or different?

Answer 8

Functionally they are same, structurally they are different

Question 9

What are Alleles and where are they located?

Answer 9

Alleles are 2 copies of a gene: One derived from the Mother and the other from the Father.
Located on homologous chromosomes

Question 10

What is a locus? (Position)

Answer 10

Position of the allele on a chromosome

Question 11

What are homologous chromosomes?

Answer 11

A pair of chromosomes, one inherited from each parent, that have corresponding gene sequences and that pair during meiosis.

Question 12

What is a genome?

Answer 12

The complete set of genes in an organism

Question 13

What is the structure of a DNA?

Answer 13

Double helix (twisted ladder)
Anti-parallel orientation

Question 14

What is the structure of a right handed double helix?

Answer 14

Sugar phosphate backbone (upright) with bases attached to sugar and lie perpendicular to backbone

Question 15

What is anti-parallel orientation of DNA?

Answer 15

• each sugar-phosphate chain runs in opposite direction
• A = T
• C = G

Question 16

What are the 3 components of DNA?

Answer 16

1. Bases (ATCG)
2. Sugar
3. Phosphate

Question 17

How does DNA serve as the genetic basis for living things? RSVE

Answer 17

1. Replication of information
2. Storage of information
3. Variation by Mutation
4. Expression of information

Question 18

What is storage of information?

Answer 18

Each somatic cell contains a complete set of chromosomes but expresses only part of the genetic information
(eg digestive cells only produce enzymes but not melanin)

Question 19

What is variation of mutation?

Answer 19

Mutation: change in the A, T, G, C sequence of DNA
Beneficial (advantage passed on) vs Bad mutations (disorder & death)

Question 20

What is expression of information?

Answer 20

DNA > transcription > mRNA -> translation > protein

Question 21

What is the structure of a nitrogenous base?

Answer 21

Complex ring structures composed of Carbon and Nitrogen atoms

Question 22

Name the 5 types of bases

Answer 22

Adenine, Thymine, Cytosine, Guanine & Uracil

Question 23

What bases do DNA contain?

Answer 23

Adenine, Thymine, Cytosine & Guanine

Question 24

What bases do RNA contain?

Answer 24

Adenine, Uracil, Cytosine & Guanine

Question 25

What are purines composed of?

Answer 25

Adenine & Guanine

Question 26

What are pyrimidines composed of? (Remember CUT)

Answer 26

Thymine, Uracil & Cytosine

Question 27

How does A pair with T?

Answer 27

2 Hydrogen bonds A === T

Question 28

How does G pair with C?

Answer 28

3 Hydrogen bonds G=_=_=_C

Question 29

What is the ratio of purines and pyrimidines?

Answer 29

1 (same number of adenine and thymine molecules same number of guanine and cytosine molecules)

Question 30

State whether RNA & DNA is oxygenated

Answer 30

RNA: ribose (Oxygenated) DNA: deoxyribose (Not oxygenated)

Question 31

What is the function of phosphoric acid?

Answer 31

Connects adjacent sugars by a phosphodiester bond

Question 32

What is DNA replication?

Answer 32

The process by which DNA makes a copy of itself

Question 33

When does DNA replication occur?

Answer 33

Occurs during interphase, prior to cell division

Question 34

What are involved in DNA replication? dEET

Answer 34

1. deoxyriboNucleosideTriPhosphate (dNTP) 2. Energy source (ATP) 3. Enzyme & proteins 4. Template DNA

Question 35

What does dNTP serve as?

Answer 35

Building blocks for DNA

Question 36

State enzymes & proteins involved in DNA replication

Answer 36

1.DNA polymerases 2.Helicase 3.SSBP (Single-stranded DNA binding proteins) 4.Gyrase/Topoisomerase 5.Primase 6.Ligase.

Question 37

What is template DNA for in DNA replication?

Answer 37

Parent base sequence that specifies the complementary sequence of the new daughter DNA

Question 38

What are the 7 steps of DNA replication?

Answer 38

1. DNA Gyrase:- unwinds the double helix 2. DNA Helicase:- Unzips the double helix 3. SSBP:- Stabilise the phosphodiester bonds between the sugar and phosphate preventing its breaking 4. Primase:- Lays down RNA primer from which nucleotide polymerization can begin 5. DNA Pol III:- Lays down complementary nucleotides in the 5’ – 3’ direction of the growing strand 6. DNA Pol I:- Removes the RNA primers and lays down DNA nucleotides instead, however it leaves phosphodiester gaps towards the 3’ end. 7. DNA Ligase:- Seals the gap in between the sugar-phosphate backbone (Okazaki fragments)

Question 39

What is leading strand?

Answer 39

polymerase travels in the same direction as the helicase.

Question 40

What is lagging strand?

Answer 40

moving away from the helicase

Question 41

What are okazaki fragments joined together by?

Answer 41

Okazaki Fragments are joined together by DNA ligase

Question 42

State the function of Gyrase/Topoisomerase in DNA replication

Answer 42

Topoisomerase/Gyrase creates nicks in DNA ahead of the replication fork to relax the supercoiling induced in the DNA by helicase activity

Question 43

What is the junction between the unwound part and the open part in DNA replication called?

Answer 43

A replication fork.

Question 44

Function of DNA helicase

Answer 44

-Breaks the hydrogen bonds between DNA strands -Helicase unwinds and separates the DNA strands so that replication can continue.

Question 45

Function of Topoisomerase

Answer 45

regulates over winding or under winding of DNA

Question 46

Function of Single-stranded DNA binding proteins (SSBPs)

Answer 46

keeps the parental strands apart

Question 47

Function of primase

Answer 47

synthesizes a RNA primer (beginning of new DNA strand synthesis)

Question 48

Function of DNA polymerase I & III

Answer 48

DNA Polymerase III: Lays down complementary nucleotides in the 5’ – 3’ direction of the growing strand DNA Polymerase I: Removes the RNA primers and lays down DNA nucleotides instead, however it leaves phosphodiester gaps towards the 3’ end.

Question 49

Function of DNA ligase

Answer 49

covalently links the Okazaki fragments together. It plays a role in repairing single-strand breaks in DNA (basically fill gaps).

Question 50

How are chromatids formed?

Answer 50

Result from the chromosome undergoing DNA replication just before cell division

Question 51

Where will a chromatid be distributed in?

Answer 51

A daughter cell

Question 52

What is a centromere and state its function.

Answer 52

Region with attachment sites for microtubules (spindle apparatus) that will move the chromosome during division

Question 53

Why is RNA Primase required before DNA Polymerase is able to synthesize new strand?

Answer 53

-DNA polymerase can only add nucleotide but cannot initiate DNA replication. -To initiate the DNA replication, the enzyme RNA Primase adds a short sequence called PRIMER to the “origin” region so that DNA replication can be started. -DNA polymerase is now able to add nucleotide and continue the DNA replication

Question 54

What can replication errors cause?

Answer 54

can cause a genetic MUTATION

Question 55

How to prevent replication errors?

Answer 55

PROOFREADING by the polymerase prevents mismatches DNA REPAIR ENZYMES can repair damaged DNA also

Question 56

What are DNA binding proteins for?

Answer 56

keep the DNA apart