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Bio 12 (1st half) > DNA Replication > Flashcards

DNA Replication Flashcards

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1
Q

Describe Nucleic Acids

A

macromolecules that encode genetic material and direct gene expression

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2
Q

What are the two nucleic acids used by human cells?

A

Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)

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3
Q

What are the monomers of Nucleic Acids?

A

Nucleotides

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4
Q

What are the three parts a Nucleotide consists of?

A

A phosphate, a pentose sugar and a nitrogenous base

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5
Q

Describe a Pentose sugar

A

It contains 5 carbons, and is used in both DNA and RNA

it is different from most sugars in our diet, which are hexose (6C)

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6
Q

Which sugar is used in DNA?

A

Deoxyribose

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7
Q

Which sugar is used in RNA?

A

Ribose

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8
Q

What is the difference between Deoxyribose and Ribose sugar?

A

Ribose has an -OH on carbon 2

Deoxyribose has an H on carbon 2
(hence de oxy)

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9
Q

Describe Phoshodiester Bonds and what do they result in making?

A

The C5 of each sugar bonds do a phosphate molecule, then react with the OH group on the C3 of another nucleotide sugar

they result in making the Sugar Phosphate Backbone

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10
Q

What are the four nucleotide bases?

A

Adenine (A), Thymine (T), Cytosine (C) and Guanine (G)

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11
Q

Where do the bases bond?

A

they bond to the C1 of the nucleotide sugar and project perpendicular to the backbone

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12
Q

What is the primary structure of DNA?

A

The sequence of nucleotide bases in a single strand of DNA

(think primary as 1D)

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13
Q

What are the two types of bases?

A

Purine and Pyrimidines

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14
Q

Describe Purines

A

The largest bases, containing two rings

adenine and guanine are purines

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15
Q

Describe Pyrimidines

A

contain only in ring, making them smaller than purines

Thymine and Cytosine are pyrimidines

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16
Q

What do all bases contain?

A

Nitrogen, making them nitrogenous

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17
Q

Describe Complimentary Base Pairing

A

The bases of one DNA strand bond to the bases of another strand, however each base can only bond with its compliment

a purine must always bond to a pyrimidine to keep the space constant

A+T and G+ C

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18
Q

What bond are formed between bases and how are they formed?

A

Hydrogen Bonds

formed when an atom (polar positive) of one base is attracted to the nitrogen of oxygen (polar negative) of another base

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19
Q

What makes hydrogen bonds different from ionic and covalent bonds?

A

they are weaker and can be broken easily

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20
Q

Describe the amount of hydrogen bonds in between the bases

A

Adenine and Thymine form 2 hydrogen bonds

Cytosine and Guanine form three hydrogen bonds

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21
Q

What is the secondary structure of DNA?

A

Complimentary Base Pairing

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22
Q

Describe Antiparallel

A

Complimentary DNA strands are antiparallel

this means that the sugar phosphate backbones face opposite directions

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23
Q

Describe the Antiparallel Strands

A

one strand is aligned 5’ to 3’ while the complimentary strand is aligned 3’ to 5’

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24
Q

What part of the DNA is hydrophilic and what part is hydrophobic?

A

The sugar phosphate backbone is hydrophilic (likes water)

the bases are hydrophobic

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25
Q

Why does DNA form a double helix?

A

to keep bases protected in the middle of the helix while the sugar phosphate backbone faces outwards

the phosphates are attracted to the hydrogens of the sugars on the following twist of the helix

26
Q

When does DNA complete one turn of the helix?

A

every 10 base pairs

27
Q

Describe the Minor Groove

A

the smallest groove that occurs where the overlapping backbones are closest together

28
Q

Describe the Major Groove

A

occurs where the gap between backbones is greatest

allows easy access for Protein Attachment

29
Q

What is the Tertiary Structure of DNA

A

the double helix

30
Q

What do DNA attach to that cause supercoiling?

A

Histone Proteins

which spool up DNA like a fishing reel to keep it compact inside the nucleus

31
Q

Describe Chromatin

A

the combination of DNA and histone proteins

32
Q

What is the Quaternary Structure of DNA?

A

Chromatin

(DNA + histones)

33
Q

What are the three steps of DNA Replication?

A

initiation

elongation

termination

34
Q

where does DNA replication occur and what are the three things it requires?

A

occurs in the nucleus

requires
1. pre-resisting DNA
2. free nucleotides
3. enzymes

35
Q

Describe Initiation

A

the first step of DNA Replication

involves unwinding the double helix and breaking hydrogen bonds

36
Q

What does the enzyme Topoisomerase do?

A

unwinds the double helix

which exposes the bases and makes it easier for other enzymes to do their job

37
Q

What does the enzyme Helicase do?

A

breaks apart the hydrogen bonds that are holding the double helix together, separating the two strands

referred to as “unzipping” the DNA

38
Q

Where does Helicase Attach?

A

to specific sites in the DNA called “origins of replication” or “Ori”

39
Q

What does Primer do?

A

after the DNA is unzipped, primers attach

primer is a short sequence of RNA that serves as a starting point for DNA synthesis (making a new strand)

(primer is usually about 20 base long)

40
Q

What is different about Primer compared to other enzymes?

A

Primer is temporary and will be replaced by nucleotides in the next stage of replication

41
Q

Describe Elongation

A

second stage of DNA replication

stage where the new DNA stands are synthesized (made)

42
Q

Describe how DNA replication is semi-conservative

A

the resulting DNA is a combination of Parent strand (pre existing DNA) and Daughter Strands (new DNA)

each copy of DNA has 1 parent strand and 1 daughter strand

43
Q

Where do Free Nucleotides Attach?

A

Free Nucleotides temporarily attach to the open DNA strand using hydrogen bonds

44
Q

What does the enzyme DNA Polymerase do?

A

DNA Polymerase synthesizes the daughter strands by fusing nucleotides together using the sugar phosphate backbone

45
Q

What is the Replication Fork?

A

the opening in the DNA behind helicase

46
Q

Describe the Leading Strand

A

the daughter strand in the replication fork being synthesized in the 5’ to 3’ direction

DNA polymerase follows continuously behind helicase when forming the leading strand

47
Q

Describe the Lagging Strand

A

the daughter strand in the replication fork being synthesized in the 3’ to 5’ direction

48
Q

What is the issue with DNA polymerase and the Lagging Strand?

A

DNA polymerase can only add nucleotides in the 5’ to 3’ direction, which is the opposite of the Lagging strand

This means that DNA Polymerase must synthesize behind the lagging strand in the OPPOSITE direction that helicase works

49
Q

Describe how DNA Polymerase works on the lagging strand

A

DNA polymerase synthesizes roughly 100 nucleotide sequences at a time before detaching and returning to the replication fork to begin a new sequence

50
Q

What are Okazaki Fragments?

A

the short sequences of lagging strand DNA

51
Q

What does the enzyme DNA Ligase do?

A

since DNA polymerase can only add one nucleotide at a time, DNA Ligase is required to fuse the Okazaki Fragments together, forming a continuous Lagging Strand.

52
Q

How do Mutations Occur?

A

When DNA polymerase fails to catch a mis-matched nucleotide pair while proofreading the daughter strands, resulting in an error

53
Q

Describe Termination

A

the third and final stage of DNA Replication

where the DNA copies are finalized and safeguarded from degradation

54
Q

Describe Termination Sites

A

Sites along the parent strands that direct helicase and DNA polymerase to detach, ending the Replication Fork

55
Q

Where do Termination Sites occur?

A

Before the last nucleotide in a DNA Strand

this means that DNA is lost every time DNA replicates

56
Q

Describe Telomeres

A

long sequences of DNA that protect the chromosome from damage

(roughly 15,000 base pairs long at birth)

human telomeres consists of the sequence TTAGGG being repeated

57
Q

What does the enzyme Telomerase do?

A

add telomeres (repetitive sequences of base pairs) after the final replication fork

Telomerase do not code for any proteins and do not contain any hereditary information

58
Q

Describe how genetic information gets lost in Termination

A

once a telomere is used up due to excessive replications, genetic information begins to get lost, severely impacting the health of the organism

59
Q

What happens to chromosomes that no longer possess telomeres?

A

They can’t replicate, meaning that cells can’t heal, grow or reproduce

60
Q

Describe the Hayflick Limit

A

the number of times that DNA can reproduce before using up its telomeres

61
Q

Describe Senescence

A

the process of shortening your telomeres over time

(cellular aging)

Bio 12 (1st half) (5 decks)

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