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Unit 1a & 1b > DNA > Flashcards

DNA Flashcards

1
Q

what is a gene?

A

a section of DNA that codes for a specific protein

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2
Q

where can you find DNA?

A

tightly coiled within a chromosome

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3
Q

what are the 4 bases within DNA?

A

adenine, thymine, guanine, cytosine

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4
Q

how many hydrogen bonds are there between cytosine and guanine?

A

3

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5
Q

how many hydrogen bonds are there between adenine and thymine?

A

2

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6
Q

how do the sugars run in the strands?

A

antiparallel

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7
Q

What is DNA an example of?

A

a polymer

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8
Q

what is DNA made from?

A

nucleotides

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9
Q

what reaction are nucleotides joined together by?

A

condensation

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10
Q

what bonds are between the nucleotides in DNA?

A

phosphodiester

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11
Q

describe the structure of a nucleotide in DNA

A

a deoxyribose sugar, a nitrogenous base and a phosphate group

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12
Q

where are the phosphodiester bonds found in the DNA?

A

in between the nucleotides, they hold them together

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13
Q

describe the structure of DNA

A

a double helix, held together by weak hydrogen bonds between complementary bases

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14
Q

describe the structure of a nucleotide in RNA

A

a ribose sugar, a nitrogenous base and a phosphate group

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15
Q

what is the monomer unit of DNA?

A

nucleotides

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16
Q

what are several nucleotides joined together called?

A

polynucleotide

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17
Q

what bases pair together in DNA?

A

A and T, C and G

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18
Q

what are the bases in RNA?

A

adenine, guanine, uracil, cytosine

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19
Q

what bases pair together in RNA?

A

adenine and uracil, cytosine and guanine

20
Q

who discovered the structure of DNA?

A

discovered by Watson and Crick with the help of X-ray crystallography from Rosalind Franklin

21
Q

name the monomer from which Nucleic Acids are made

A

nucleotides

22
Q

describe the structure of RNA

A

single stranded, the strands are much shorter, contains ribose sugar, thymine is replaced by uracil.

23
Q

describe the role of DNA Helicase in DNA replication

A

separates the 2 strands and breaks the hydrogen bonds between bases.

24
Q

describe the role of DNA Polymerase in DNA replication

A

runs along and joins the sugar phosphate backbone (adjacent nucleotides) by forming phosphodiester bonds.

25
Q

describe the role of DNA ligase in DNA replication

A

joins the Okazaki fragments

26
Q

if a strand of DNA contains 14% T, how much C does it contain?

A

36%

27
Q

why did some scientists doubt that DNA carried the genetic code when it was discovered?

A

the chemical composition was relatively simple

28
Q

describe the basic structure of a DNA nucleotide. How does it differ to an RNA nucleotide?

A

DNA is a nucleotide made of deoxyribose, a phosphate group and either A, T, C or G. RNA contains ribose instead and T is replaced by U

29
Q

why is the semi-conservative replication of DNA so important?

A

this allows genetic continuity between generations since cell division produces an exact copy of the DNA

30
Q

describe the theory of semi-conservative DNA replication

A

the parent DNA molecule separates into its 2 strands, each of which acts as a template for the formation of a new complementary strand. The two daughter molecules therefore contain half the parent DNA and half the new DNA

31
Q

who presented the semi-conservative hypothesis and what did they know?

A

Meselsohn and Stahl knew that all the bases in DNA contain nitrogen and it has 2 forms, light 14N and heavy 15N isotope and that bacteria will incorporate nitrogen from their growing medium into any new DNA they make

32
Q

what is an isotope?

A

same number of protons and electrons but different number of neutrons

33
Q

describe and explain how the structure of DNA results in accurate replication

A

There is 2 strands so semi conservative replication is possible. Hydrogen bonds hold strands together and can be easily broken by DNA helicase. Bases are exposed so they can act as a template

34
Q

why is DNA helicase important in DNA replication?

A

it separates the 2 strands in the DNA and breaks the hydrogen bonds between bases so nucleotides can attach

35
Q

describe the role of the enzyme primate in DNA replication

A

makes a primer so that the enzyme DNA polymerase can bind to the DNA

36
Q

explain the leading strand in DNA replication

A

is made in a continuous strand as free nucleotides bind with their complementary bases

37
Q

explain the lagging strand in DNA replication

A

runs in the opposite direction (5 to 3) to the leading strand so DNA polymerase isn’t complementary so DNA can only be added in small chunks called Okazaki Fragments which are later joined by DNA ligase

38
Q

explain the structure of the end of the DNA strand

A

each end of a DNA strand is slightly different to its structure. One is called the 3’ end and one end is called the 5’ end.

39
Q

which end of DNA is DNA polymerase complementary to?

A

the 3’ end of the original strand

40
Q

describe the process of DNA replication

A

step 1: DNA helicase breaks the H bonds between bases so 2 strands are separated.
step 2: each OG strand acts as a template (replication fork formed). This is SC replication. Free floating nucleotides are attracted to their C base pairing on the OG strands.
step 3: Condensation reactions join the nucleotides together. This is catalysed by DNA polymerase. New H bonds form between bases.
Each new DNA molecule contains one OG strand and one new strand

41
Q

what happens in the growing on 15n stage (step 1)?

A

the E.coli bacterium is grown in a 15n medium. 15n is an isotope so it can be detected when compared to a DNA containing 14n. The original strand of DNA bases only contain 15n which is heavy

42
Q

what happens in the transferring stage (15n to 14n, step 2)?

A

this is the first gen. Some of the bacteria is transferred to a 14n medium and is replicated. The new strands made are now hybrid. Any DNA formed will contain bases with 14n as the bacteria replicate. After the 1st gen, DNA will be made up of 1 strand of 15n and 1 of 14n. This is why the band appears in the middle

43
Q

what happens in generation 2 stage in semi conservative replication?

A

after a second gen, half of the DNA will be hybrid but half will be light 14n only. The proportion of the bands change because with each generation, more and more DNA is light 14n and there’s a lower proportion of hybrid strands

44
Q

describe and explain how the structure of DNA results in accurate replication

A

the weak hydrogen bonds between bases can be easily broken by helicase. There’s 2 strands therefore semi-conservative replication is possible. Hydrogen bonds hold strands together. Bases are exposed so they can act as a template.

45
Q

what type of DNA molecule is present in the first sample in semi conservative replication?

A

DNA with 2 strands of 15n

46
Q

what type of DNA molecule is present in the second sample in semi conservative replication?

A

strands containing 14n and 15n

47
Q

what type of DNA molecule is present in the third sample in semi conservative replication?

A

strands containing 15n and 14n along with strands with only 14n

Unit 1a & 1b (17 decks)

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