Chapter 4 - 4.4: Molecular Biology Flashcards
1
Q
Name the 2 nucleic Acids
A
DNA: Deoxyribonucleic Acid
RNA: Ribonucleic Acid
2
Q
Define Nucleic Acid
A
Found in the nucleus
Possess many acidic phosphate groups
3
Q
Define nucleosides
A
Glycosylamines that are essentially nucleotides without their phosphate group
Consist of a nucleobase and a 5 carbon sugar
4
Q
What are the 3 components of nucleotides?
A
1) 5 carbon pentose sugar (deoxyribose/ ribose)
2) aromatic nitrogenous base
3) 1-3 phosphate groups
5
Q
What are the two classes of Nucleotides?
A
Purines and Pyrimidines
6
Q
What are purines?
A
Derived from precursors called purine
Include nucleotide Bases G and A
7
Q
What are pyrimidines?
A
Aromatic heterocyclic organic compound similar to pyridine
Include nucleotide bases C, T and U
8
Q
How does a nucleotide differ from a nucleoside ?
A
Nucleoside: 2 components, essentially nucleotide without its phosphate group (sugar with a nucleobase [purine or pyrimidine] linked at 1’ carbon)
Nucleotide: phosphate esters of nucleosides with 1, 2 or 3 phosphate groups joined
9
Q
What is a nucleoside triphosphate (NTP)? If it has a deoxyribose sugar, it is then called dNTP.
A
Nucleotides with 3 phosphate groups
10
Q
What do we call nucleotides with 3 phosphate groups?
A
Nucleoside triphosphate (NTP) or dNTP if deoxyribose sugar
11
Q
Name the 3 pyrimidine nucleotide bases
A
Cytosine
Thymine (DNA)
Uracil (RNA)
12
Q
Name 2 purine nucleotide bases
A
Adenine
Guanine
13
Q
What part of the nucleotide is considered variable? Which two are invariable?
A
Variable: the base (A, T, C, U, G)
Invariable: Sugar and Phosphate groups (referred to as “backbone” of DNA)
14
Q
Define polynucleotides
A
nucleotides linked together by phosphodiester bonds
15
Q
How are nucleotides linked to form polynucleotides?
A
Phosphodiester bonds : 2 hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form 2 ester bonds
3’ hydroxy group of one deoxyribose and the 5’ phosphate group of the next link
16
Q
Define Oligonucleotide
A
A polymer of several nucleotides linked together
17
Q
Define polynucleotide
A
A polymer of many nucleotides
18
Q
Which end of the chain is written first in a polynucleotide?
A
The end of the chain with a free 5’ phosphate group is written first
The other nucleotides are read in 5’ to 3’ direction
19
Q
What is a product of the polymerization of nucleotides?
A
pyrophosphate
20
Q
Which scientists developed a model of the structure of DNA in the cell?
A
James Watson and Francis Crick
Helped by Maurice Wilkins and Rosalind Franklin
21
Q
What is the Watson Crick model?
A
Portrays cellular DNA as a right handed double helix held together by Hydrogen bonds between bases
22
Q
Are the nucleotides in polynucleotide chains hydrogen bonded together in a parallel or antiparallel orientation ?
A
Antiparallel: the 5’ end of one chain is paired with the 3’ end of the other
23
Q
Which nucleotide bases hydrogen bond with which?
A
H bonded pairs always consist of one purine and one pyrimidine
A is always bonded to T (U for RNA)
G is always bonded to C
24
Q
How many H bonds does a G-C nucleotide pairing have?
A
3 H-bonds
25
How many H bonds does an A-T nucleotide pairing have?
2 H-bonds
26
What makes 2 chains of DNA complimentary?
If the bases in each strand match up and can Hbond when the strands are oriented in antiparallel
27
What is a kilobase pair (Kbp)?
dsDNA of 1000 nucleotides long
28
What is annealing or hybridization?
The binding of 2 complementary strands of DNA into a double helix
29
What do we call The binding of 2 complementary strands of DNA into a double helix ?
Annealing or hybridization
30
What do we call the separation of 2 strands of complementary DNA?
Melting or Denaturation
31
What is melting or denaturation ?
The separation of 2 complementary DNA strands
32
Which are true about dsDNA?
i) If the fraction of purines and total molecular weight of a double helix are known, the amount of cytosine can be calculated
ii) If the amount of G in a ds is known, the amount of C can be calculated
iii) The oligonucleotide ATGTAT is complementary to the oligonucleotide ATACAT
iv) The 2 chains in a piece of dsDNA containing mostly purines will be bonded together more tightly than the 2 chains containing mostly pyrimidines
ii and iii are correct
i) Incorrect: the ratio of purines to pyrimidines is always the same (50:50) since each purine (A G) is paired with a pyrimidine (C U T)
ii) Correct: for every G theres a C, for every A theres a T
iii) Correct: strands are antiparallel. A and T pair, G and C pair, and the 5' end is always written first
iv) Incorrect: ratio is always 50:50. However, 2 chains containing mostly GC pairs will bond more tightly than 2 chains containing mostly AT pairs (3 H-bonds vs 2)
33
What is Chargoff's Rule?
Concept that tells us how to calculate the # of purines if we know the # of pyrimidines or vice versa
[A] = [T] and [G] = [C]
and [A] + [G] = [T] + [C]
34
What does it mean when we say that DNA is coiled?
It corkscrews in a clockwise motion
Bases are interior
Ribose/ phosphate backbone are exterior
35
What stabilizes the DNA double helix?
Van der Waals interactions between the bases stacked upon each other
36
Define genome
The sum total of al an organisms genetic info
37
Define a Eukaryote
An organism composed of one or more cells containing visibly evident nuclei and organelles
Nucleus enclosed within a nuclear envelope
38
What do we call pieces of eukaryotic genomes composed of several large pieces of dsDNA?
Chromosomes
39
How many chromosomes do humans have? How many come from each parent?
46 chromosomes total
23 from each parent
40
Define prokaryote
bacterial, single celled organism lackign a nucleus and other membrane bound organelles
41
How are prokaryotic genomes stored?
prokaryotic genomes are composed of a single circular chromosome
Viral genomes may be linear or circular DNA or RNA
42
How many base pairs approximately do human genomes have? Bacterial genomes?
Human: over 10^9 base pairs
Bacterial: only 10^6
43
Is there correlation between genome size and evolutionary sophistication?
No. The organisms with largest known genomes are amphibians
44
Why cant DNA remain as a simple double helix free floating in the cell?
It would be bulky and fragile
45
Define Supercoil.
A DNA double helix that has undergone additional twisting since DNA cannot remain as a simple double helix free floating in the cell
46
What act in prokaryotes is the equivalent to supercoiling in DNA double helixes?
prokaryotes have a mechanism to make their single circular chromosome more compact and sturdy
47
Why would active exonucleases be floating free in the cell?
2 potential reasons
1) mRNA has a very short lifespan: degraded rapidly and more is made if protein is still needed.
This is consistent with the idea that regulation of gene expression occurs primarily at the transcriptional level since this is more efficient.
2) Viruses may inject RNA into the cell. If it does not have the correct cap and tail modifications, exonucleases will destroy it
48
One piece of RNA isolated from a human cell is found to produce two different polypeptides when added to a cell free protein synthesis system containing all the enzymes necessary for eukaryotic gene expression. When the two polypeptides are separated and digested with trypsin, they produce fragments of the following molecular weights:
Polypeptide 1: 5 kD, 8 kD, 12 kD, and 14 kD
Polypeptide 2: 3 kD, 5 kD, 8 kD, 10 kD, 12 kD, and
14 kD
How can we explain the synthesis of two different polypeptides from one piece of RNA?
This is an example of the use of splicing for the regulation of gene expression
The piece of RNA must have been hnRNA. In the cell free system it underwent "differential splicing" to produce one of two different mRNA molecules
It appears that polypeptide 1 came from an mRNA which had more material spliced out than the mRNA coding for polypeptide 2.
49
What is DNA gyrase?
Explain its function.
DNA gyrase is an enzyme that uses energy of ATP to twist DNA
Gyrase functions by breaking DNA and twisting the two sides of the circle around each other. This results in a twisted circle like structure composed of dsDNA
50
Do eukaryotes or prokaryotes have more DNA in their genome?
What does this imply for packing?
Eukaryotes do
Therefore requires denser packaging to fit within the cell
51
What are histones?
Globular proteins that eukaryotic DNA is wrapped around for storage
52
What are the globular proteins that eukaryotes wrap their DNA around for storage called?
histones
53
What are nucleosomes?
Bead-looking, composed of DNA wrapped around an octamer of histones (8)
54
Appearing bead-looking, these are composed of DNA wrapped around an octamer of histones (8).
Nucleosomes
55
What is the name of the space between nucleosomes?
It is a length of double helical DNA
Linker DNA
56
What is Linker DNA
It is a length of double helical DNA that makes up the space between nucleosomes
57
Define Chromatin
Fully packed DNA, but not condensed
DNA wrapped around histone proteins or DNA and histone proteins
58
What do we call fully packed, but not yet condensed DNA?
Chromatin
59
Which bonds make up nucleotides into oligo/polynucleotides ?
phosphodiester bonds
60
Which bonds make up complimentary polynucleotides into DNA double helix?
H bonds
61
DNA double helix + DNA gyrase = ?
super coils
62
Super coils + ____ = nucleosomes
8 histones
63
DNA double helix + _____= super coils
DNA gyrase
64
____ + DNA gyrase = super coils
DNA double helix
65
Super coils + 8 histones = ?
nucleosomes
66
_______ + 8 histones = nucleosomes
super coils
67
Describe the process of compacting DNA double helix to Chomosomes?
DNA double helix + DNA gyrase = supercoils
Supercoils + 8 histones= nucleosomes
nucleosomes ---> chromatin ---> Chromosome
68
What are the differences between chromatin, chromosome, and chromatid?
Chromatin: fully packed DNA, not yet condensed
Chromosome: chromatin after it has been condensed
Chromatid: Duplicated chromosome attached at centromere
69
Define centromere
The region of the chromosome to which the spindle fibres attach during cell division
70
The region of the chromosome to which the spindle fibres attach during cell division
The centromere
71
Define Kinetochores
Multi-protein complexes that act as attachment sites for spindle fibres during cell division
72
Multi-protein complexes that act as attachment sites for spindle fibres during cell division
Kinetochores
73
Define Spindle Fibres
They form a protein structure that divides the genetic material in a cell
These are necessary to equally divide the chromosome in a parental cell into 2 daughter cells during mitosis and meiosis
74
They form a protein structure that divides the genetic material in a cell
These are necessary to equally divide the chromosome in a parental cell into 2 daughter cells during mitosis and meiosis
Spindle Fibres
75
What are the 2 main components of centromeres?
Heterochromatin and repetitive DNA sequences
76
What is heterochromatin?
Chromosome material of different density from normal (usually greater), in which the activity of the genes is modified or suppressed
Compare with euchromatin.
77
What is Euchromatin ?
Chromosome material which does not stain strongly except during cell division. It represents the major genes and is involved in transcription.
Compare with heterochromatin.
78
What are the 2 types of "arms" that chromosomes have?
p (short) and q (long) arms
79
Describe the metacentric chromosome
Even p and q arm distribution
80
Describe the submetacentric chromosome
approx 1/3 is p arm
2/3 q arm
81
Describe acrocentric chromosome
approx 1/4 is p arm
3/4 is q arm
82
Describe Telocentric chromosome
all q arm, no p arm
83
Define telomeres
The ends of linear chromosomes
At DNA level these regions are distinguished by a distinct nucleotide sequence repeat 50 to hundreds of times
84
The ends of linear chromosomes
At DNA level these regions are distinguished by a distinct nucleotide sequence repeat 50 to hundreds of times
Telomeres
85
a) How long are repeated units in telomeres usually?
b) Which nucleotide are they rich in?
c) What repeated sequence is common in many vertebrates (humans, mice, etc)
a) 6-8 bps long, repeated
b) usually Guanine rich
c) 5' - TTAGGG - 3'
86
Are telomeres composed of single or double stranded DNA? Explain why.
Telomeres are composed of both
Single stranded is found at the very end of the chromosome and is approx 300 bp long
It loops to form a knot, held together with many telomere associated proteins
This stabilizes the end of the chromosome.
Specialized telomere cap proteins distinguish telomeres from double stranded breaks so to prevent activation of repair pathways
87
What is the ultimate function of telomeres?
To prevent chromosome deterioration and prevent fusion with neighbouring chromosomes
Function as "disposable buffers", blocking the ends of chromosomes
88
Would prokaryotic DNA have telomeres?
No. Many prokaryotes have circular genomes so their DNA does not have telomeres
89
How many autosomes does the human genome have?
22
90
How many sex chromosomes do humans have?
2 different sex chromosomes
91
How many base pairs does the human genome have?
How many genes does the human genome code for?
a) 3.2 billion bps
b) 21, 000 genes
92
What are Intergenic regions? What are they largely composed of?
Separate the regions of the human genome with high transcription rates.
Composed of noncoding DNA with no clear function (contains some direction and regulation for genes)
Tandem repeats and Transposons
93
Define Gene
A DNA sequence that encodes a gene product
94
What are Single nucleotide Polymorphisms (SNPs or "snips") ?
Single nucleotide variations
Occur once in ever 1,000 bps
Essentially small mutations
95
Single nucleotide variations
Occur once in ever 1,000 bps
Essentially small mutations
Single Nucleotide Polymorphisms (SNPs or "snips")
96
If the size of the human genome is just over 3 billion bps and Single Nucleotide Polymorphisms (SNPs) occur ever 1,000 bps, how many human SNPs are there?
3 x 10^9 bps x 1 SNP / 1000bps= 3 x 10^6 SNPs or approx 3 million human SNPs
97
Where do SNPs most often occur?
What happens if an SNP occurs in a coding region of the genome?
a) In non coding regions of genome
b) Can lead to specific traits and phenotypes ex. PTC sensitivity
70% of people taste PTC as bitter and 30% dont taste it at all
98
Define Copy Number Variations
Structural variations in the genome that lead to different copies of DNA sections
Large regions of genome can be duplicated or deleted
Specific mechanism isnt clear but potentially d/t misalignment of repetitive DNA sequences during synapsis of homologous chromosomes in meiosis
99
How do SNPs (Single Nucleotide Polymorphisms) differ from CNVs (Copy number variation) ?
compared to SNPs, CNVs apply to much larger regions of the genome
100
What are the effects of CNVs (copy number variation) ?
CNVs are a normal part of our genome but also can be associated with cancer and diseases
Genes involved in immune system function and brain development activity are often enriched in CNVs
101
Define Haploid
Give examples
The presence of a single set of chromosomes in an organisms cell
Only the egg and sperm cells in humans are haploid
102
Define Diploid
Give examples
The presence of 2 complete sets of chromosomes in an organisms cells, with each parent contributing a chromosome to each set
Humans are diploid. Most of the body's cells contain 23 chromosome pairs
103
a) What are Tandem Repeats?
b) In which situations are they considered irregular?
c) In which 4 situations do they serve functional purpose?
a) Short sequences of nucleotides are repeated one after the other from 3 to over 100 times
b) Repeats can be unstable if the repeating unit is short (di or trinucleotides) or if it is very long. Unstable tandem repeats can lead to chromosome breaks and some are implicated in disease
c) (1) Heterochromatin, (2) centromeres, and (3) telomeres are all rich in repeats
(4) DNA fingerprinting: Tandem repeats vary in length between individuals
104
What is considered, the "template" for production of another nucleic acid: RNA?
Genes : sequences of nucleotides
105
What is the difference between transcription and translation of the genetic code?
Transcription: the process of reading DNA and writing info as RNA (occurs in the nucleus)
- this CAN produce a final gene product (non coding RNAs) or a messenger molecule (mRNA)
- mRNA is used to construct proteins
Translation: The synthesis of proteins using RNA as template
- accomplished in the cytoplasm (E and P) by the ribosome, a massive enzyme composed of proteins and pieces of rRNA ( ribosomal RNA)
106
What is known as the Central Dogma (Fundamental Law) of molecular biology?
DNA --> RNA --> protein
107
What is the smallest codon size that would allow the 4 letter nucleotide alphabet to encode 20 different amino acids?
4^1= 4 X
4^2= 16 X
4^3= 64 Correct
3 nucleotides is the minimum codon size
108
Define codon
A 3 letter nucleic acid word that codes for a particular amino acid
109
Why is uracil shown on the genetic code chart and why is Thiamine absent?
RNA is the nucleic acid that actually encodes protein (for amino acids) during translation and Uracil is only in RNA.
110
Using the Genetic Code Chart:
The codon GTG in DNA is transcribed in RNA as _____, that ribosome translates into which amino acid?
the transcribed RNA codon is CAC (complimentary to GTG) which if you look at the chart codes for histidine
111
Using the Genetic Code Chart:
The genetic code was studied by experimenters using a cell free protein synthesis system. All the materials necessary for protein synthesis (Ribosomes, amino acids, tRNA, GTP, ATP) were purified and placed in a beaker. Then synthetic RNA was added and protein was translated from this template. For ex. When synthetic RNA containing only cytosine (CCC...) was added, polypeptides containing only proline (polyproline) resulted. What kind of synthetic RNA would give rise to a mixture of polyproline, polyhistidine, and polythreonine?
The RNA would have to be CCACCACCACCACCA...
This yields polyproline if read as CCA CCA CCA CCA
But if read as CAC CAC CAC it would give rise to polyhistidine
If read as ACC ACC ACC ACC it would encode to polythreonine
112
How many codons total are there? How many of them specify amino acids? What do the rest of them do?
64 total
61 specify amino acids
The rest (3) are stop codons.
113
Using the Genetic Code:
If the last nucleotide in the codon CUU is changed in a gene that codes for protein, will the protein be affected?
What is the name of this phenomenon?
No because CU_ codes for leucine no matter what the 3rd nucleotide is
These 2+ codons that code for the same amino acid are known as synonyms
114
These are 2+ codons that code for the same amino acid.
Synonyms
115
What are three aspects of molecular biology that arent explicitly stated in the Central Dogma?
1. Some viruses (retroviruses) make DNA from RNA using the enzyme reverse transcriptae
2. Info can be transferred other ways (ex. DNA methylation + Post translational modification of proteins can alter gene expression and convey info even though neither is included in the central dogma )
3. Many final gene products are not proteins but are RNAs instead
116
What is known as the control centre of the cell?
The DNA genome
117
What is Replication of DNA?
Mitosis produces 2 identical daughter cells from one parental cell
Each daughter must have the same genome as the parent
This is an enzymatic process (much like the Krebs cycle or glycolysis )
118
What is old DNA called in the replication process? New DNA?
old: parental DNA
new: Daughter DNA
119
Which scientists did experiments to determine if DNA replication is semiconservative, conservative, or dispersive?
Meselson and Stahl
120
Is DNA replication Conservative, Dispresive or Semiconservative?
Semiconservative
Individual strands of the double stranded parent are pulled apart then a new daughter strand is synthesized using parental DNA as a template to copy
121
What is Conservative DNA replication?
Parental dsDNA remains as is and an entirely new double stranded genome is created
122
What is Dispersive DNA Replication?
Both copies of the genomes composed of scattered pieces of new and old DNA.
123
What is semiconservative DNA replication?
AFter replication, one strand of the new double helix is parental (old) and one strand is newly synthesized daughter DNA
124
What is helicase?
An enzyme that unwinds the double helix and separates the strands of DNA to be replicated
125
What needs to be done to DNA before it can be replicated?
Replication cannot occur unless the double helix is uncoiled and separated into 2 single strands by helicase
126
How does helicase know where to begin unwind DNA for replication?
IT begins to unwind at a specific location (sequence of nucleotides) on the chromosome called the origin of replication (ORI)
This sequence is found by proteins with tertiary structure to specifically recognize a particular pattern of nucleotides. These scan along chromosomes until they find the ORI and then call in helicase and other enzymes for DNA replication initiation
127
What is the ORI (Origin of replication)?
How is it found in DNA replication?
How does this differ between Eukaryotes and Prokaryotes
A sequence of nucleotides on the chromosome that tells helicase where to start unwinding for replication
This sequence is found by proteins with tertiary structure to specifically recognize a particular pattern of nucleotides. These scan along chromosomes until they find the ORI and then call in helicase and other enzymes for DNA replication initiation
Prokaryotes use a protein called DnaA to find the ORI
Eukaryotes have 3 proteins cooperate to find the ORI
128
How is the ORI found in Eukaryotes?
3 proteins cooperate to find the ORI
2 of these proteins are synthesized during M and G phases of the cell cycle
These proteins link DNA replication to the cell cycle, ensuring DNA replication doesnt initiate during other phases of the cell cycle
129
What is responsible for replication initiation in prokaryotes?
DnaA
130
What are the 2 top problems that helicase create?
What are the structures that resolve these problems?
#1: When helicase unwinds at ORI, the helix winds tighter up and downstream from the ORI. Without topoisomerase (to unwrap the helix to relieve tension), the chromosome would tangle and eventually break.
#2: Single stranded DNA is much less stable than dsDNA. Single stranded binding proteins (SSBPs) protect DNA thats been unpackaged in prep for replication and keeps strands separated.
131
What is known as an open complex in the replication process?
Separated strands ready for replication!
132
What is the role of topoisomerases?
Enzymes that cut one or both strands and unwrap the helix, releasing tension created by helicase
133
What is the role of Single stranded binding proteins? (SSBPs)
These protect DNA thats been unpackaged in prep for replication and keeps strands separated in an open complex
134
What is the primosome?
a protein complex responsible for creating RNA primers for DNA replication
Its central component is RNA polymerase
135
What is RNA polymerase?
Enzymes that catalyze the synthesis of DNA/RNA polymers whose sequence is complementary to the original template
136
What is primase ?
A type of RNA polymerase: plays role in synthesis of RNA primer
137
Why is primer synthesis by RNA polymerase important for DNA replication?
Because the next enzyme, DNA polymerase, cannot start a new DNA chain from nothing, it can only add nucleotides to an existing nucleotide chain
138
What is DNA polymerase and what does it do?
DNA pol catalyzes elongation of daughter strand using the parental template
It elongates the primer made by RNA polymerase by adding dNTPs to its 3' end
139
What direction is the template strand READ in for DNA replication?
If the daughter strand must be made 5' to 3', and the opposite strand must be read for it to be complementary and antiparallel, the template must be read 3' to 5'
140
What is the replisome? What are its three main components?
This is a large complex of proteins
It carries out replication of DNA
1. helicase
2. DNA polymerase
3. Primase
141
Does prokaryotic or Eukaryotic replisome contain more components? Why?
Eukaryotic has more proteins
Additional complexity in eukaryotic system required because replication machinery must also unwind DNA from histone proteins
142
In the process of replication, do primers on both sides elongate strands towards the same direction? or opposite? why?
The primers will elongate towards opposite ends of the chromosome because the template strands are antiparallel
143
Which structure in replication checks each new nucleotide to make sure the correct base pair has been formed before incorporating into the growing polymer?
DNA polymerase
144
What process is the thermodynamic driving force for the polymerization reaction in DNA replication?
The removal and hydrolysis of pyrophosphate from each dNTP added to the chain
145
List the 7 replication rules to remember
1. DNA replication is semiconservative
2. Polymerization occurs in the 5' to 3' direction without exception
3. DNA pol requires a template
4. DNA pol requires a primer
5. Replication forks grow away from the origin in both directions
6. Leading strand replication is continuous. Lagging strand replication is discontinuous
7. All RNA primers are eventually replaced by DNA
146
What direction does polymerization occur in?
5' to 3'
147
Does replication proceed away or towards the origin of replication?
Away from the ORI
148
Define Replication forks
The areas where the parental double helix continues to unwind
149
Which strand must wait for the replication fork to widen before continuing to polymerize?
Which strand grows leading into the replication fork?
Lagging strands
Leading strand
150
What are Okazaki Fragments?
Small chunks of DNA comprising the lagging strand
151
As the replication forks grow, does helicase have to continue to unwind the double helix and separate the strands?
Yes
152
What joins Okazaki Fragments ?
DNA Ligase
153
How many DNA polymerase enzymes do eukaryotes have?
How many do Prokaryotes have? What are they?
a) several different DNA polymerase enzymes
b) 5: DNA Polymerase I, II, III, IV, and V
(only really need to know functions of I and III
154
DNA pol III function in prokaryotes
What special function does it have?
Responsible for the super fast, super accurate elongation of the leading strand
Has 5' to 3' polymerase activity but also 3' to 5' exonuclease activity
155
What is exonuclease?
What are the 2 important types ? How do they differ?
A function of Prokaryotic DNA pol I and III
Can cut a polynucleotide chain in the middle of the chain, usually a particular sequence. Means "to cut a nucleic acid chain"
Two important types are repair enzymes and restriction enzymes:
- Repair enzymes: remove chemically damaged DNA from the chain
- Restriction enzymes: Endonucleases found in bacteria. Destroy DNA of infecting viruses, restricting the host range of the virus
156
Proofreading function
3 to 5 exonuclease activity in which the enzyme moves backwards to chop off the nucleotide it just added if incorrect
The ability to correct mistakes in this way
157
Prokaryotic DNA pol III is most known as ____
Prokaryotic DNA pol I is important for ____
Replicative enzyme. Has no known function in repair
Excision repair `=
158
Roles of prokaryotic DNA pol II, IV, and V
II: Has 5' to 3' activity and 3' to 5' proofreading function. Participates in DNA repair pathways and backup for DNA pol III
IV and V: Both are error prone in 5' to 3' polymerase activity. These function to stall other polymerase enzymes at replication forks when DNA repair pathways have been activated, an important part of prokaryotic checkpoint pathway
159
If a bacterium has a mutation in the gene for DNA pol III resulting in an enzyme without the 3' to 5' exonuclease activity, will mutations occur more often than in bacteria with a normal DNA pol gene
Yes: the 3' to 5' exonuclease functions to edit polymerase's work
without editing, many more point mutations would occur due to incorporation of the wrong nucleotides. Normal polymerase is very adept at sensing correct bps and removing bases that dont belong
160
What do we call prokaryotic replication, based on the shape its chromosome takes on?
Replication of prokaryotes is said to proceed by the theta mechanism and is called theta replication
Prokaryotes have 1 chromosome which is circular and so as replication proceeds, the partially duplicated genome starts looking like the greek letter theta
161
In Eukaryotic Replication, when many replicating forks continue to widen, they create the appearance of bubbles along the DNA strand referred to as ______
replication bubbles
Eventually replication forks meet and the separate daughter strands are ligated together
162
Replication Bubbles in Eukaryotic Replication
when many replicating forks continue to widen, they create the appearance of bubbles along the DNA strand
This is because Eukaryotic Chromosomes are large and so they have many origins to start the replication process
163
What are telomeres and how do they function?
Telomeres are disposable repeats at the ends of chromosomes
These are consumed and shorten during cell division. When they become too short, the chromosome can no longer replicate ----> result: cells can activate DNA repair pathways, enter a senescent state, or activate apoptosis
164
What does it mean if a cell enters a senescent state?
Biological aging, the gradual deterioration of functional characteristics in living organisms: alive but not dividing
Something that can happen when telomeres at the ends of chromosomes become too short to a critical length where the chromosome can no longer replicate. Many age related diseases are linked to telomere shortening
165
What is the Hayflick limit ?
The number of times a normal human cell type can divide until telomere length stops cell division
166
Telomerase
An enzyme that adds repetitive nucleotide sequences to the ends of chromosomes thus lengthening telomeres
Is a robinucleoprotein complex, contains an RNA primer, and reverse transcriptase enzymes (generates complimentary DNA from RNA template)
167
In most organisms, telomerase is only expressed in what types of cells?
embryonic stem cells (germ line)
some WBCs
Cancer cells: helps cells immortalize, allowing the bypass of senescence and apoptosis
