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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
DNA replication is a
Semi-conservative model of replication
26
Each nucleotide that is added to a growing DNA strand is a
Nucleoside triphosphate, adenine, thymine guanine or cytosine triphosphate. (dATP, dTTP, dGTP & dCTP)
27
DNA polymerases add nucleotides only to the free ___
3' end of a growing strand
28
A new DNA strand can elongate only in the
5' to 3' direction
29
The copying of DNA is
remarkably fast and accurate
30
An E.coli cell has a ____ circular chromosome of about ______ nucleotide pairs which can be replicated to form 2 daughter cells in ~ __ hour.
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
Humans have __ chromosomes that contain about _______ nucleotide pairs yet one cell take only ___ to replicate all the DNA
46 6 billion a few hours
32
More than a dozen enzyme and other proteins
participate in DNA replication
33
DNA replication starts at sites called
Origins of replication
34
In circular chromosome of E. coil how many sites of origin of replications are there?
only one origin of replication
35
An origin of replication is a
short stretch of DNA with a particular sequence of bases
36
What happens at the origin of replication in E.coli
* 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
In linear chromosomes of eukaryotes how many origins of replication are there?
MANY
38
in Linear chromosome what happens at the origins of replication
- 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
Separation of DNA strands at the Replication fork; what happens at the forks?
DNA strands are being unwound
40
Separation of DNA strands at the Replication fork; & PROTEINS
Several proteins participate in the unwinding of parental DNA strand including topoisomerases, helicases and single strand binding protein
41
Topoisomerase
Topoisomerase corrects “overwinding” ahead of replica6on forks by breaking, swiveling, and rejoining DNA strands
42
Helicases:
Helicases are enzymes that untwist the double helix at the replica6on forks
43
Single-stranded binding proteins
Single-strand binding proteins bind to and stabilize single-stranded DNA
44
The RNA primer is
Short and the 3' end serves as the starting point for the new DNA strand
45
What are the enzymes called that
catalyse the synthesis of new DNA at a replication fork.
46
In E.coli there are several different DNA polymerases but ________ are important.
DNA polymerase III and I (DNA pol III and DNA pol I)
47
In eukaryotes there are at least ___ different DNA polymerases discovered so far but the general principles are the same
11
48
Most DNA polymerases require a
Primer and a DNA template strand
49
In E.coli DNA pol ||| adds a
DNA nucleotide to the 3' end of the primer and then continues to add DNA nucleotides
50
DNA polymerases cannot initiate _____ they can only _____
synthesis of a polynucleotide; they can only add nucleotides to the 3ʹ end.
51
The initial nucleotide strand is a
short RNA primer
52
Primase:
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
Synthesis of leading strand: | Along one template strand DNA pol III can synthesize
a complimentary strand continuously by elongating the DNA in the mandatory 5’ to 3’ direction.
54
Synthesis of leading strand: | DNA pol lll remains
in the replication fork on that template strand continuously adding nucleotides to the new complimentary strand as the fork progresses.
55
Synthesis of lagging strand: | to elongate the new strand
called the lagging strand, DNA polymerase must work in the direction away from the replication for
56
The lagging strands synthesised as a series of segments called
Okazaki fragments
57
Synthesis of lagging strand: | Primate synthesises short
RNA primer
58
Synthesis of lagging strand: DNA pol lll
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
Synthesis of lagging strand: | DNA pol l
then replaces the RNA primer with DNA nucleo6des.
60
Okazaki fragments are joined together by
DNA ligase
61
DNA replication machine:
The proteins that participate in DNA replication form a large complex
62
Recent studies support a model in which DNA polymerase molecules
“reel in” parental DNA and “extrude” newly made daughter DNA molecules
63
the DNA replication machine may be
stationary during the replication process
64
A chromosome consists of
a DNA molecule packed together with proteins
65
The bacterial chromosome is a
double-stranded, circular DNA molecule associated with a small amount of protein.
66
In bacterium DNA is
"supercoiled" and found in a region of the cell called the NUCLEOID
67
Eukaryotic chromosomes have:
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
Chromosomes fit into the nucleus through an
elaborate, multi-level system of packing
69
Histones:
Proteins which are responsible of the first level of picking in chromatin
70
The nucleosome consist of
DNA wound twice around a protein core composed of 2 | molecules of each of the 4 main histone types.
71
Next level of packing in eukaryotic chromosome results from
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
the 30 nm fibre forms loops called
looped domains attached to a chromosome scaffold made of proteins thus making up a 300 nm fibre.
73
In mitotic chromosome the looped domains themselves:
coil in a way that is not fully understood compacting the chromatin to produce a characteristic metaphase chromosome (700 nm in width)
74
Histones :
H2A, H2B, H3, H4 | + H1 at later stage

APS 138: Molecular and cell biology (15 decks)

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