Bio Lect8 Flashcards
1
Q
What carries genetic information?
A
DNA
DNA is the molecule that contains the genetic instructions for the development and function of living things.
2
Q
Who conducted experiments on peas in the 1860s that led to the idea of units of inheritance?
A
Mendel
Mendel’s experiments established the fundamental principles of heredity.
3
Q
What term was later used to describe the ‘units of inheritance’ discovered by Mendel?
A
Genes
Genes are segments of DNA that contain the instructions for building proteins.
4
Q
What did Morgan study to understand the location of genes?
A
Drosophila (fruit flies)
Morgan’s work with fruit flies helped establish the chromosomal theory of inheritance.
5
Q
What characteristics did Morgan examine in Drosophila?
A
Eye colour and wing size
These traits were used to track inheritance patterns in his experiments.
6
Q
What substance did Miescher isolate in the 1860s from pus cells?
A
Nuclein (DNA)
Miescher’s discovery was pivotal in identifying DNA as the carrier of genetic information.
7
Q
What were chromosomes known to contain?
A
DNA and proteins
The discovery that chromosomes contained these components was crucial for understanding genetics.
8
Q
What was the initial suspicion about the ‘inheritance factor’ before DNA was understood?
A
Protein
Many scientists believed proteins were responsible for heredity before DNA was identified.
9
Q
Fill in the blank: DNA was isolated from _______ cells by Miescher.
A
pus
Miescher’s work involved analyzing discarded surgical bandages to extract nuclein.
10
Q
What did Griffith’s experiment demonstrate?
A
Bacterial transformation
11
Q
What was the outcome when mice were injected with the virulent S strain?
A
Mouse died
12
Q
What was the outcome when mice were injected with the non-virulent R strain?
A
Mouse survived
13
Q
What happened when mice were injected with heat-killed S strain?
A
Mouse survived
14
Q
What was the result when a mix of heat-killed S strain and live R strain was injected into mice?
A
Mouse died
15
Q
What surprising observation was made in the dead mouse after the injection of heat-killed S strain and live R strain?
A
Live S strain bacteria appeared
16
Q
How did the R strain bacteria become virulent in Griffith’s experiment?
A
R strain absorbed genes from the dead S strain
17
Q
What genetic trait did the R strain gain from the dead S strain?
A
The capsule
18
Q
What conclusion did Griffith’s experiment lead to regarding bacteria?
A
Bacteria can transfer genetic traits
19
Q
What was later confirmed as the genetic material following Griffith’s findings?
A
DNA
20
Q
What is transformation in the context of genetics?
A
A change in genotype & phenotype due to assimilation of external DNA by a cell
Transformation is a key process in molecular biology and genetics, often studied in bacteria.
21
Q
Who carried on Griffith’s work and made significant discoveries about DNA?
A
Avery
22
Q
What substances did Avery systematically destroy in his experiments?
A
Lipids, carbohydrates, proteins, and ribonucleic acid (RNA)
23
Q
What was the result of Avery destroying all components except DNA?
A
Horizontal gene transformation still occurred until DNA was destroyed
24
Q
What substance did Avery use to block transformation, and kill DNA?
A
Deoxyribonuclease
25
What was the first indication that DNA was the inheritance factor?
Transformation was blocked only when DNA was destroyed
26
What happened to the mouse when live S strain was introduced?
Mouse dies
27
What was the outcome when DNA was destroyed in the experiment?
Mouse lives
28
Fill in the blank: Avery's experiments indicated that _______ was the inheritance factor.
DNA
29
What did the Hershey-Chase experiment demonstrate?
DNA is the genetic material, not protein.
30
What were the two groups of phages used in the Hershey-Chase experiment?
Batch 1: labeled with radioactive sulfur (³⁵S) for proteins
Batch 2: labeled with radioactive phosphorus (³²P) for DNA
31
What was the purpose of labeling the phages in the experiment?
To mark their proteins or DNA.
32
What process did the phages undergo to infect bacterial cells?
The phages injected their genetic material into the bacteria.
33
What was used to separate the empty phage shells from the bacterial cells?
A blender.
34
What was the purpose of centrifugation in the experiment?
To separate heavier bacterial cells from lighter phage shells.
35
What was found in the liquid after centrifugation in Batch 1?
Radioactivity, indicating proteins stayed outside the bacteria.
36
What was found in the pellet after centrifugation in Batch 2?
Radioactivity, indicating DNA entered the bacteria.
37
What distinguishes DNA from protein in the context of the experiment?
There is no sulfur in DNA.
38
What was the conclusion of the Hershey-Chase experiment?
DNA, not protein, is the genetic material because only DNA entered the bacteria and directed the production of new viruses.
39
What did Erwin Chargaff find about the composition of DNA in 1947?
The composition of DNA differed between species, indicating molecular diversity amongst species.
40
What was Chargaff's finding regarding DNA within a species?
Within a species, the DNA from all cells had the same composition.
41
What are the base pairing percentages found by Chargaff?
G = C and A = T (within experimental error).
42
What are the percentage compositions of bases in all human cells according to Chargaff's findings?
* A = 30.9%
* T = 29.4%
* G = 19.9%
* C = 19.8%
43
What is DNA known to be a polymer of?
Nucleotides
## Footnote
Nucleotides consist of a base, sugar, and phosphate.
44
What is the sugar component of DNA?
2'-deoxyribose
## Footnote
2'-deoxyribose is a 5-carbon sugar.
45
What are the four types of nitrogenous bases in DNA?
* Adenine (A)
* Cytosine (C)
* Guanine (G)
* Thymine (T)
## Footnote
These bases pair in specific ways (A with T, C with G).
46
Which nitrogenous bases are classified as purines?
* Adenine (A)
* Guanine (G)
## Footnote
Purines have a structure of 2 fused rings.
47
Which nitrogenous bases are classified as pyrimidines?
* Cytosine (C)
* Thymine (T)
## Footnote
Pyrimidines have a structure of 1 ring.
48
What is the backbone of DNA composed of?
Sugar-phosphate
## Footnote
The sugar-phosphate backbone provides structural support.
49
What defines the 5' end of a DNA molecule?
The phosphate group
## Footnote
The 5' end is where the phosphate is attached to the fifth carbon of the sugar.
50
What defines the 3' end of a DNA molecule?
The hydroxyl group
## Footnote
The 3' end is where the hydroxyl group is attached to the third carbon of the sugar.
51
Fill in the blank: Each nucleotide consists of a base, the sugar ______, and a phosphate.
deoxyribose
## Footnote
Deoxyribose is the sugar involved in DNA structure.
52
What is DNA’s backbone made up of?
A sugar-phosphate backbone
53
What type of sugar is found in DNA?
Deoxyribose
54
Why is the sugar in DNA described as hydrophilic?
It is highly charged
55
What is the significance of the 3' carbon in DNA?
It is where the next nucleotide is attached
56
Where are the nitrogenous bases located in the DNA structure?
In the center of the helix
57
Why are nitrogenous bases located in the center of the helix?
Because they are hydrophobic
58
At which end of the DNA can a nucleotide be added?
The 3' end
59
What group is attached to the 5' end of the DNA?
A phosphate group
60
What replaces the hydroxyl group at the 3' end during nucleotide addition?
The phosphate group of the incoming nucleotide
61
What type of bond is formed when a nucleotide is added to the DNA strand?
A phosphodiester bond
62
Fill in the blank: The hydroxyl group (-OH) at the 3' end is replaced by the _______ of the incoming nucleotide.
phosphate group
63
What shape was DNA known to be from X-ray diffraction experiments?
Helical
## Footnote
This finding was established by Wilkins and Franklin in the early 1950s.
64
Who conducted the X-ray diffraction experiments that contributed to the understanding of DNA's structure?
Wilkins and Franklin
## Footnote
Their work was pivotal in the early 1950s.
65
What did Watson deduce from the X-ray diffraction data regarding DNA?
Width of helix and spacing of nitrogenous bases
## Footnote
This deduction was essential for understanding DNA's structure.
66
Who made the crucial step in understanding the structure of DNA in 1953?
Watson and Crick
67
What is the idea proposed by Watson and Crick regarding DNA structure?
Specific base pairing within a double helical structure
68
In DNA, which base pairs with adenine (A)?
Thymine (T)
69
In DNA, which base pairs with guanine (G)?
Cytosine (C)
70
What type of bonds are responsible for the pairing of bases in DNA?
Hydrogen bonds
71
Fill in the blank: An A on one strand pairs with a _______ on the other.
T
72
Fill in the blank: A G on one strand pairs with a _______ on the other.
C
73
What orientation do the DNA strands have?
Anti-parallel (5'-3' and 3'-5')
## Footnote
This orientation is crucial for replication and function.
74
How many base pairs are there per turn of the DNA double helix?
10 base pairs per turn
## Footnote
This contributes to the helical structure of DNA.
75
Where are the bases located in the DNA structure?
On the inside (non-polar hydrophobic)
## Footnote
This arrangement protects the bases from the aqueous environment.
76
What are the properties of the phosphate groups in DNA?
Polar, hydrophilic and located on the outside
## Footnote
This allows for interaction with the aqueous environment.
77
What do space-filling models of DNA show?
A major and a minor groove in the double helix
## Footnote
These grooves are important for protein binding.
78
Fill in the blank: The sugar-phosphate backbone of DNA provides _______.
Structural support
## Footnote
It forms the sides of the DNA ladder, maintaining its integrity.
79
True or False: The strands of DNA run parallel to each other.
False
## Footnote
They run anti-parallel, which is crucial for their function.
80
What type of structure does the parent molecule of DNA have?
Two complementary strands of DNA
## Footnote
Each strand is made of nucleotides paired by hydrogen bonds.
81
Which bases pair together in DNA?
A with T and G with C
## Footnote
These pairs are held together by hydrogen bonding.
82
What is the first step in DNA replication?
Separation of the two DNA strands
## Footnote
This allows each strand to serve as a template.
83
What role do parental strands play during replication?
Serve as templates that determine the order of nucleotides
## Footnote
This is essential for forming new complementary strands.
84
How are nucleotides connected in new DNA strands?
To form the sugar-phosphate backbones
## Footnote
This connection is crucial for maintaining the structure of DNA.
85
What does each 'daughter' DNA molecule consist of?
One parental strand and one new strand
## Footnote
This is a result of the semi-conservative nature of DNA replication.
86
What type of mechanism is DNA replication termed as?
Semi-conservative
## Footnote
The semi-conservative model contrasts with conservative and dispersive models.
87
Who conducted the experiment that provided evidence for the semi-conservative model of DNA replication?
Meselson and Stahl (1958)
## Footnote
Their experiment was pivotal in demonstrating the semi-conservative nature of DNA replication.
88
In the conservative model of DNA replication, what happens to the parental strands?
They reassociate after acting as templates for new strands
## Footnote
This restores the parental double helix.
89
In the semi-conservative model, what occurs to the strands of the parental molecule during replication?
They separate and each functions as a template for synthesis of a new, complementary strand
## Footnote
This results in each daughter DNA molecule containing one parental and one new strand.
90
What characterizes the dispersive model of DNA replication?
Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA
## Footnote
This model suggests that DNA replication does not conserve any original strands.
91
What organism was used in the DNA replication experiment?
Escherichia coli
92
What isotopes of nitrogen were used to distinguish between old and new DNA?
15N and 14N
93
What method was used to separate the two types of DNA based on density?
Density gradient centrifugation
94
How much denser is 15N-DNA compared to 14N-DNA?
About 1% more dense
95
What was the conclusion regarding the model of DNA replication based on the experiment's results?
The results were only consistent with the semi-conservative model
96
After how many minutes was the DNA sample centrifuged after the first replication?
20 minutes
97
What type of model does the semi-conservative model refer to?
DNA replication
98
After how many minutes was the DNA sample centrifuged after the second replication?
40 minutes
99
Fill in the blank: DNA replication is elegantly simple, but the _______ is complex.
biochemistry
100
What are the three models of DNA replication mentioned?
* Conservative model
* Semi-conservative model
* Dispersive model
101
What initiates the replication of DNA?
Replication starts at specific origins of replication
## Footnote
One origin in prokaryotes, many in eukaryotes.
102
What is the role of proteins in DNA replication?
Proteins recognise the DNA sequence and bind to it, opening up the double helix.
103
What structure is formed during DNA replication?
Replication bubbles with Y-shaped replication forks.
104
What are the two types of strands involved in DNA replication?
Parental (template) strand and Daughter (new) strand.
105
How do replication bubbles function during DNA replication?
Bubbles expand laterally as DNA replication proceeds in both directions.
106
What happens to replication bubbles as DNA replication continues?
Eventually, the replication bubbles fuse and synthesis of the daughter strands is complete.
107
In eukaryotes, where does DNA replication begin?
At many sites along the giant DNA molecule of each chromosome.
108
What is a replication fork?
A Y-shaped structure where new strands are being elongated during DNA replication.
109
Fill in the blank: In eukaryotes, DNA replication begins at many sites where the parental strands separate to form _______.
replication bubbles.
110
True or False: In prokaryotes, DNA replication starts at multiple sites.
False.
111
What visual evidence can be used to observe replication bubbles in cells?
Micrographs, such as those from a cultured Chinese hamster cell.
112
What is the outcome of DNA replication?
Two daughter DNA molecules.
113
What is the main function of DNA polymerases?
To elongate DNA strands by adding nucleotide units.
114
What sources do DNA polymerases use for nucleotide units?
Triphosphates (ATP, GTP, etc.)
115
What is released when a nucleotide is added to the growing DNA chain?
Pyrophosphate (a two-phosphate unit).
116
What is the rate of DNA elongation in humans?
50 nucleotides a second.
117
How many different DNA polymerases have been identified in eukaryotes?
Over 10 different DNA polymerases.
118
Nucleotides can ONLY be added to which end of the DNA strand?
The free 3' end.
119
True or False: Nucleotides can be added to the 5' end of DNA.
False.
120
What is the speed at which DNA polymerase checks complementary bases?
50 nucleotides a second.
121
Fill in the blank: DNA polymerases use _______ as a source of nucleotide units.
[triphosphates]
122
What is the significance of the rate of DNA elongation?
It allows for the rapid copying of the genome.
123
What are the two types of DNA strands during replication?
Leading strand and lagging strand
## Footnote
The leading strand undergoes continuous replication, while the lagging strand undergoes discontinuous replication.
124
In which direction do enzymes extend DNA chains?
5' → 3'
## Footnote
This directionality is crucial for understanding how DNA replication occurs.
125
What is the replication process for the leading strand?
Continuous replication
## Footnote
The leading strand is synthesized continuously as the DNA unwinds.
126
What is the replication process for the lagging strand?
Discontinuous replication
## Footnote
The lagging strand is synthesized in short segments known as Okazaki fragments.
127
What enzyme is responsible for synthesizing DNA on the leading strand?
DNA pol III
## Footnote
DNA pol III plays a key role in DNA synthesis during replication.
128
Which enzyme synthesizes RNA primers during DNA replication?
Primase
## Footnote
Primase is essential for providing the starting point for DNA synthesis.
129
What role does DNA ligase play in DNA replication?
Joins Okazaki fragments
## Footnote
DNA ligase connects the short segments of the lagging strand after they are synthesized.
130
What is the function of DNA pol I during replication?
Replaces RNA primers with DNA
## Footnote
DNA pol I removes RNA primers and fills the gaps with DNA nucleotides.
131
Fill in the blank: The leading strand is synthesized in a _______ manner.
continuous
## Footnote
This refers to the uninterrupted nature of the leading strand's synthesis.
132
Fill in the blank: The lagging strand is synthesized in a _______ manner.
discontinuous
## Footnote
This refers to the segmented synthesis of the lagging strand.
133
What is the function of Helicase in bacterial DNA replication?
Unwinds parental double helix at replication forks
## Footnote
Helicase is essential for separating the DNA strands to allow replication.
134
What role does Single-strand binding protein play during DNA replication?
Binds to and stabilizes single-stranded DNA until it can be used as a template
## Footnote
This prevents the strands from re-annealing or forming secondary structures.
135
What is the function of Topoisomerase in DNA replication?
Corrects 'overwinding' ahead of replication forks by breaking, swiveling, and rejoining DNA strands
## Footnote
Topoisomerase helps relieve the tension that builds up ahead of the replication fork.
136
What does Primase do in the context of DNA replication?
Synthesizes a single RNA primer at the 5' end of the leading strand and at the 5' end of each Okazaki fragment
## Footnote
Primase is crucial for initiating DNA synthesis as DNA polymerases require a primer.
137
What is the function of DNA polymerase III?
Continuously synthesizes the leading strand, adding on to the primer
## Footnote
DNA polymerase III is the primary enzyme involved in DNA synthesis.
138
What is the role of DNA polymerase I?
Removes primer from the 5' end of leading strand and replaces it with DNA, adding on to the adjacent 3' end
## Footnote
DNA polymerase I is also involved in repairing DNA and replacing RNA primers with DNA.
139
What does DNA Ligase do in DNA replication?
Joins the 3' end of the DNA that replaces the primer to the rest of the leading strand and joins the Okazaki fragments
## Footnote
Ligase is essential for sealing nicks in the sugar-phosphate backbone of the DNA.
140
Fill in the blank: The function of _______ is to unwind the parental double helix at replication forks.
Helicase
141
True or False: Single-strand binding proteins are responsible for synthesizing RNA primers during DNA replication.
False
## Footnote
Single-strand binding proteins stabilize single-stranded DNA, while Primase synthesizes RNA primers.
142
What is the function of Topoisomerase in relation to replication forks?
Corrects 'overwinding' ahead of replication forks by breaking, swiveling, and rejoining DNA strands
143
Fill in the blank: DNA Ligase joins the _______ fragments during DNA replication.
Okazaki
144
What are Okazaki fragments?
Frags of the lagging strand, typically 100-200 nucleotides in length
## Footnote
Okazaki fragments are formed during DNA replication on the lagging strand.
145
What enzyme joins Okazaki fragments?
DNA ligase
## Footnote
DNA ligase is responsible for sealing the nicks between Okazaki fragments.
146
What can DNA polymerases do?
Only extend a pre-existing strand
## Footnote
DNA polymerases cannot initiate synthesis and require a primer.
147
How does DNA replication start?
By making a short primer of RNA, about 10 nucleotides long
## Footnote
This RNA primer is essential for DNA polymerases to begin synthesis.
148
What happens to the RNA primer after DNA synthesis?
It is later replaced by DNA
## Footnote
The replacement ensures that the final product consists entirely of DNA.
149
What is the nature of DNA replication?
Extremely rapid and accurate
## Footnote
DNA replication is crucial for cell division and maintaining genetic fidelity.
