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APS 138: Molecular and cell biology > Lecture 4: Molecular basis of inheritance > Flashcards

Lecture 4: Molecular basis of inheritance Flashcards

1
Q

Your genetic endowment is your

A

DNA, contained in the 46 chromosomes you inherited from your parents.

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2
Q

Nucleic acids are

A

unique in their ability to direct their own replication.

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3
Q

The resemblance of offspring to their parents depends on

A

the precise replication of DNA and its transmission from one generation to the next.

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4
Q

It is this DNA program that directs the development of..

A

biochemical, anatomical, physiological, and (to some extent) behavioral traits.

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5
Q

Who used X-ray crystallography to study the molecular structure of DNA

A

Maurice Wilkins and Rosalind Franklin

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6
Q

Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that:

A

– DNA was helical,
– the width of the helix
– the spacing of the nitrogenous bases
– the DNA molecule was made up of two strands, forming a double helix

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7
Q

DNA: in April 1953

A

James Watson and Francis Crick proposed the double-helical model for the structure of DNA

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8
Q

DNA: in 1962

A

Crick, Watson and Wilkins were awarded the Nobel prize in Physiology/ Medicine.

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9
Q

DNA

A

deoxyribonucleic acid

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10
Q

DNA is a polymer of ____ each consisting of

A

NUCLEOTIDES

  • A nitrogenous base, thymine, adenine, cytosine or guanine
  • A sugar, deoxyribose
  • A phosphate group
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11
Q

Nitrogenous bases of DNA

A
  • Thymine
  • Adenine
  • Cytosine
  • Guanine
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12
Q

Structure of DNA;

formation of sugar phosphate backbone

A

The P group of one nucleotide is attached to the sugar of the next to form the ‘backbone’ of the DNA molecule

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13
Q

Structure of DNA directionality:

A

from the 5’ end with the P group to the 3’ end with the OH group of the sugar.

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14
Q

DNA: 5’ refers to

A

the specific carbon of the sugar molecule to which the P group is attached

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15
Q

DNA: 3’ refers to

A

the carbon in the sugar molecule with the OH group.

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16
Q

The double helix of DNA is due to

A

the base pairing rules of the different nitrogenous bases.

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17
Q

Adenine and guanine are

A

purines with 2 organic rings.

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18
Q

Thymine (Uracil) and cytosine are

A

pyrimidines with a single ring

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19
Q

Adenine always pairs with thymine via

A

2 hydrogen bonds

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20
Q

Guanine pairs with cytosine via

A

3 hydrogen bonds

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21
Q

the two strands of DNA run

A

anti parallel to each other

5’ —–3’
3’——5’

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22
Q

The two strands are held together by

A

hydrogen bonds between the bases in the interior of the double helix

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23
Q

Watson and Crick noted that the specific base pairing suggested a

A

possible copying mechanism for genetic material

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24
Q

Each ‘daughter’ DNA molecule consists of

A

one parental strand and one new strand

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25
Q

DNA replication is a

A

Semi-conservative model of replication

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26
Q

Each nucleotide that is added to a growing DNA strand is a

A

Nucleoside triphosphate, adenine, thymine guanine or cytosine triphosphate. (dATP, dTTP, dGTP & dCTP)

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27
Q

DNA polymerases add nucleotides only to the free ___

A

3’ end of a growing strand

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28
Q

A new DNA strand can elongate only in the

A

5’ to 3’ direction

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29
Q

The copying of DNA is

A

remarkably fast and accurate

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30
Q

An E.coli cell has a ____ circular chromosome of about ______ nucleotide pairs which can be replicated to form 2 daughter cells in ~ __ hour.

A

An E.coli cell has a single circular chromosome of about 4.6 million nucleotide pairs which can be replicated to form 2 daughter cells in ~ 1 hour.

31
Q

Humans have __ chromosomes that contain about _______ nucleotide pairs yet one cell take only ___ to replicate all the DNA

A

46

6 billion

a few hours

32
Q

More than a dozen enzyme and other proteins

A

participate in DNA replication

33
Q

DNA replication starts at sites called

A

Origins of replication

34
Q

In circular chromosome of E. coil how many sites of origin of replications are there?

A

only one origin of replication

35
Q

An origin of replication is a

A

short stretch of DNA with a particular sequence of bases

36
Q

What happens at the origin of replication in E.coli

A
  • Parental strands separate at the origin forming a replication bubble.
  • The replication bubble has a fork at each end.
  • Replication proceeds in both directions from each fork until the forks meet resulting in two daughter cells
37
Q

In linear chromosomes of eukaryotes how many origins of replication are there?

A

MANY

38
Q

in Linear chromosome what happens at the origins of replication

A
  • Parental strands separate at the origins of replication forming replication bubbles.
  • The replication bubbles have fork at either end.
  • Replication bubbles expand as replication proceeds in both directions from each fork.
  • Eventually the bubbles fuse resulting in the synthesis of two daughter molecules.
39
Q

Separation of DNA strands at the Replication fork; what happens at the forks?

A

DNA strands are being unwound

40
Q

Separation of DNA strands at the Replication fork; & PROTEINS

A

Several proteins participate in the unwinding of parental DNA strand including topoisomerases, helicases and single strand binding protein

41
Q

Topoisomerase

A

Topoisomerase corrects “overwinding” ahead of replica6on forks by breaking, swiveling, and rejoining DNA strands

42
Q

Helicases:

A

Helicases are enzymes that untwist the double helix at the replica6on forks

43
Q

Single-stranded binding proteins

A

Single-strand binding proteins bind to and stabilize single-stranded DNA

44
Q

The RNA primer is

A

Short and the 3’ end serves as the starting point for the new DNA strand

45
Q

What are the enzymes called that

A

catalyse the synthesis of new DNA at a replication fork.

46
Q

In E.coli there are several different DNA polymerases but ________ are important.

A

DNA polymerase III and I (DNA pol III and DNA pol I)

47
Q

In eukaryotes there are at least ___ different DNA polymerases discovered so far but the general principles are the same

A

11

48
Q

Most DNA polymerases require a

A

Primer and a DNA template strand

49
Q

In E.coli DNA pol ||| adds a

A

DNA nucleotide to the 3’ end of the primer and then continues to add DNA nucleotides

50
Q

DNA polymerases cannot initiate _____ they can only _____

A

synthesis of a polynucleotide; they can only add nucleotides to the 3ʹ end.

51
Q

The initial nucleotide strand is a

A

short RNA primer

52
Q

Primase:

A

is an enzyme that starts an RNA chain from scratch adding RNA nucleotides one at a tie using the parental DNA as a template

53
Q

Synthesis of leading strand:

Along one template strand DNA pol III can synthesize

A

a complimentary strand continuously by elongating the DNA in the mandatory 5’ to 3’ direction.

54
Q

Synthesis of leading strand:

DNA pol lll remains

A

in the replication fork on that template strand continuously adding nucleotides to the new complimentary strand as the fork progresses.

55
Q

Synthesis of lagging strand:

to elongate the new strand

A

called the lagging strand, DNA polymerase must work in the direction away from the replication for

56
Q

The lagging strands synthesised as a series of segments called

A

Okazaki fragments

57
Q

Synthesis of lagging strand:

Primate synthesises short

A

RNA primer

58
Q

Synthesis of lagging strand: DNA pol lll

A

starts DNA synthesis at the 3’ end of the primer and con6nues in the 5’ to 3’ direc6on un6l it reaches the fragment ahead

59
Q

Synthesis of lagging strand:

DNA pol l

A

then replaces the RNA primer with DNA nucleo6des.

60
Q

Okazaki fragments are joined together by

A

DNA ligase

61
Q

DNA replication machine:

A

The proteins that participate in DNA replication form a large complex

62
Q

Recent studies support a model in which DNA polymerase molecules

A

“reel in” parental DNA and “extrude” newly made daughter DNA molecules

63
Q

the DNA replication machine may be

A

stationary during the replication process

64
Q

A chromosome consists of

A

a DNA molecule packed together with proteins

65
Q

The bacterial chromosome is a

A

double-stranded, circular DNA molecule associated with a small amount of protein.

66
Q

In bacterium DNA is

A

“supercoiled” and found in a region of the cell called the NUCLEOID

67
Q

Eukaryotic chromosomes have:

A

Linear DNA molecules associated with a large amount of protein. The complex of DNA and protein is called chromatin, and chromosomes are found in the nucleus of eukaryotic cells.

68
Q

Chromosomes fit into the nucleus through an

A

elaborate, multi-level system of packing

69
Q

Histones:

A

Proteins which are responsible of the first level of picking in chromatin

70
Q

The nucleosome consist of

A

DNA wound twice around a protein core composed of 2

molecules of each of the 4 main histone types.

71
Q

Next level of packing in eukaryotic chromosome results from

A

interactions between the histone tails of one nucleosome and the linker DNA and nucleosomes on either side. A fifthh histone (H1) is involved.
-The interactions cause the fibre to coil forming a chromatin fibre 30 nm thick

72
Q

the 30 nm fibre forms loops called

A

looped domains attached to a chromosome scaffold made of proteins thus making up a 300 nm fibre.

73
Q

In mitotic chromosome the looped domains themselves:

A

coil in a way that is not fully understood compacting the chromatin to produce a characteristic metaphase chromosome (700 nm in width)

74
Q

Histones :

A

H2A, H2B, H3, H4

+ H1 at later stage

APS 138: Molecular and cell biology (15 decks)

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