Chapter 5: Chemical Basis of Heredity Flashcards
(86 cards)
1
Q
Four major characteristics that a molecule should possess to be a genetic material
A
-Replication
-Storage of information
-Expression of information
-Variation by mutation
2
Q
a fundamental property of all living organisms
A
Replication-
3
Q
to act as a repository of genetic information that may or may not be
expressed by the cell in which it resides.
A
Storage of information
4
Q
charac:
the basis of the process of information flow within the cell
A
Expression of information
5
Q
what happens during transcription of DNA
A
which three main types of RNA molecules
are synthesized: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA
(tRNA)
6
Q
what happens to mRNA during DNa translation
A
translation, the chemical information in mRNA directs the construction of a chain of
amino acids, called a polypeptide, which then folds into a protein
7
Q
if a change in the chemical composition of DNA—occurs, the alteration may be
A
reflected
during transcription and translation, affecting the specific protein
8
Q
initiated by the work of
Frederick Griffith (1972)
A
Oswald Avery,
Colin MacLeod, and Maclyn McCarty’s (1944
9
Q
initial event that led to the acceptance of DNA as the genetic material.
A
publication on the chemical nature of a “transforming principle” i
10
Q
he experimented with several different strains of the bacterium Diplococcus
pneumoniae
A
Frederick Griffith
11
Q
kind of strains experiemneted by griffith
A
Some were virulent strains, which cause pneumonia in certain vertebrates (notably
humans and mice), while
avirulent strains, which do not cause illness.
12
Q
what bacteria form smooth colonies (S) with a shiny surface when grown on an
agar culture plate
A
Encapsulated bacteria
13
Q
Its DNA frequently appears as a distinct clump, called the nucleoid, which is confined to a definite region of the cytoplasm.
A
Bacterial Chromosomes
14
Q
- fundamental repeating units of chromatin, which are composed of 200 base
pairs of DNA, an octamer of four types of histones, plus one linker histone.
A
NUCLEOSOMES
15
Q
The two basic types of chromatin are
which undergoes the normal process of condensation and decondensation
in the cell cycle
A
euchromatin
16
Q
The two basic types of chromatin are
which remains in a highly condensed state throughout the cell cycle,
even during interphase
A
Heterochromatin-
17
Q
5 abundant types of chromatin
A
: H1, H2A, H2B, H3, and H4
18
Q
An essential function of the genetic material and must be executed precisely for genetic
continuity between cells to be maintained following cell division
A
replication or synthesis of DNA
19
Q
is the mode used by bacterial
cells to produce new DNA molecules
A
semi conservative replication
20
Q
who published the results of an experiment
providing strong evidence that semi conservative replication is the mode used by bacterial cells to produce new DNA molecules
A
In 1958, Matthew Meselson and Franklin Stahl
21
Q
the only nitrogen source.
A
15NH4Cl (ammonium
chloride
22
Q
what technique referred in the experimental procedure in meselson and stahl
A
sedimentation
equilibrium centrifugation (also called buoyant density gradient centrifugation)
23
Q
3 Requirements of Replication
A
- A template consisting of single-stranded DNA
- Raw materials (substrates) to be assembled into a new nucleotide strand
- Enzymes and other proteins that “read” the template and assemble the substrates into a
DNA molecule
24
Q
a common type of replication that takes place in circular DNA, such as that
found in E. coli and other bacteria
A
Theta replication
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the loop generated from the unwinding of the double helix
Replication bubble-
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the point of unwinding, where the two single strands separate from the
double-stranded DNA helixthe point of unwinding, where the two single strands separate from the
double-stranded DNA helix
Replication fork-
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If there are two replication forks, one at each end of the replication bubble, the forks proceed
outward in both directions in a process called
bidirectional replication
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If there are two replication forks, one at each end of the replication bubble, the forks proceed
outward in both directions in a process called bidirectional replication, simultaneously
unwinding and replicating the DNA until they eventually meet.
* If a single replication fork is present, it proceeds around the entire circle to produce two
complete circular DNA molecules, each consisting of one old and one new nucleotide strand.
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bind to oriC and cause a short section of DNA
to unwind. This unwinding allows helicase and other single-strand-binding proteins to
attach to the polynucleotide strand.
Initiator proteins (known as DnaA in E. coli)
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breaks the hydrogen bonds that exist between the bases of the two
nucleotide strands of a DNA molecule. Helicase cannot initiate the unwinding of double
dna helicase
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After DNA has been unwound by helicase, what is attached
single-strand-binding proteins (SSBs) attach
tightly to the exposed single-stranded DNA. These proteins protect the single- stranded nucleotide chains and prevent the formation of secondary structures that interfere with
replication.
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a topoisomerase which control the supercoiling of DNA. It reduces the
torsional strain (torque) that builds up ahead of the replication fork as a result of
unwinding by making a double-strand break in one segment of the DNA helix, passing
another segment of the helix through the break, and then resealing the broken ends of
the DNA. This action removes a twist in the DNA and reduces the supercoiling
DNA gyrase
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Two major types of topoisomerase:
a. type I- alter supercoiling by making single-strand breaks in DNA
b. type II- create double-strand breaks in DNA
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an enzyme that synthesizes short stretches of RNA nucleotides, or primers
Primase
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short stretch (about 10–12 nucleotides long) of RNA nucleotides, which provides
a 3’-OH group for the attachment of DNA nucleotides to start DNA synthesis. (Because
primase is an RNA polymerase, it does not require a preexisting 3’-OH group to start the
synthesis of a nucleotide strand.
primers
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On the leading strand, where DNA synthesis is continuous, a primer is required only at the
5’ end of the newly synthesized strand.
* On the lagging strand, where replication is discontinuous, a new primer must be generated
at the beginning of each Okazaki fragment.
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is a large multiprotein complex that acts as the main workhorse of
replication. It synthesizes nucleotide strands by adding new nucleotides to the 3’ end
of a growing DNA strand).
DNA polymerase III
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what will happen if If a nucleotide with an
incorrect base is inserted into the growing DNA strand,
DNA polymerase III uses its
3-5’ exonuclease activity to back up and remove the incorrect nucleotide. It then
resumes its 5’à3’ polymerase activity. These two functions together allow DNA
polymerase III to efficiently and accurately synthesize new DNA molecules.
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, DNA polymerase I also possesses 5’à3’ exonuclease activity, which is used
to remove the primers laid down by primase and replace them with DNA nucleotides
by synthesizing in a 5’à3’ direction
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main function of DNA polymerase I.
primase and replace them with DNA nucleotides
by synthesizing in a 5’à3’ direction. The removal and replacement of primers appears
to constitute
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is encoded by a gene whose transcription is activated by disruption of DNA synthesis
at the replication fork.
Polymerase
II
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catalyzes the formation of a
phosphodiester bond without adding another nucleotide to the strand.
DNA ligase
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Synthesizes a short RNA primer to
provide a 3¢-OH group for the
attachment of DNA nucleotides
dna primase
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blocks the movement of helicase, thus stalling the replication fork and
preventing further DNA replication.
tus-ter complex
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newly synthesized DNA formed from the continuous DNA synthesis
Leading strand
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resulting from discontinuous DNA synthesis on the opposite DNA
template
* Lagging strand-
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small fragments containing 1000 to 2000 nucleotides which
are converted into longer and longer DNA strands of higher molecular weight as
synthesis proceeds. RNA primers are part of each such fragment.
* Discontinuous synthesis of DNA requires enzymes that both remove the RNA
primers and unite the Okazaki fragments into the lagging strand
okazaki fragments
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steps in transcription
initiation
elongation
termination
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the initial step, in bacteria it is established when the RNA polymerases
subunit recognizes specific DNA sequences called promoters located in the region
upstream (5ʹ) from the point of initial transcription of a gene
Template binding
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step in which in which DNA is threaded through RNA polymerase, and the polymerase unwinds
the DNA and adds new nucleotides, one at a time, in a 5ʹ to 3ʹ extension, creating a
temporary DNA/RNA duplex whose chains run antiparallel to one another
elongation
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the recognition of the end of the transcription unit and the separation of the
RNA molecule from the DNA template
termination
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intervening sequences
introns (“in” for intervening) that are spliced out
(by spliceosome) before the mature mRNA is translated.
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Those that are retained and
expressed in the amino acid sequence of the proteins they encode are
exons (“ex”
for expressed)
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Decodes the information in mRNA, leading to the synthesis of polypeptide chains
Involves the interactions of mRNA, tRNA, ribosomes, and a variety of translation factors
essential to the initiation, elongation, and termination of the polypeptide chain
* Proteins, the final product of most genes, achieve a three-dimensional conformation that is
based on the primary amino acid sequences of the polypeptide chains making up each protein.
* The function of any protein is closely tied to its three-dimensional structure, which can be
disrupted by mutation.
translation
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developed the one-gene, one-enzyme hypothesissuggested that genes function by encoding enzymes and that each gene encodes a
separate enzyme. Later on it was modified to become the one-gene, one polypeptide
hypothesi
george Beadle and Edward Tatum
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Each amino acid molecule consists of a
central carbon atom bonded to an amino group,
a hydrogen atom, a carboxyl group, and an R (radical) group that differs for each amino
acid
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The amino acids in proteins are joined together by
peptide bonds (to form polypeptide
chains; a protein consists of one or more polypeptide chains.
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Primary structure of a protein-
is its sequence of amino acids
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Secondary structure
produce through interactions between neighboring amino acids,
creating the folds and twists.
Two common secondary structures found in proteins
are the beta (β) pleated sheet and the alpha (α) helix.
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produced when secondary structures interact and fold which is the
overall, three-dimensional shape of the protein. The secondary and tertiary structures
of a protein are ultimately determined by the primary structure—the amino acid
sequence—of the protein
Tertiary structure-
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some proteins consist of two or more polypeptide chains that
associate that associate with each other.
Quaternary structure-
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central to all living processes such as the enzymes, the biological catalysts that
drive the chemical reactions of the cell
Regulation
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providing scaffolding and support for membranes, filaments, bone, and hair (ex.
Collagen and keratin
Structural-
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Transport oxygen- ex
ex. Hemoglobin and myoglobin
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Movement ex
. Actin, myosin and tubulin
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Communication
neurotransmitters
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Defense
ex. immunoglobulins
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type regulation of gene expression that stimulate gene expression
Positive control
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type regulation of gene expression that inhibit gene expression
Negative control
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A group of bacterial structural genes that are transcribed together, along with their
promoter and additional sequences that control their transcription
Operon
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- those in which transcription is normally off (not taking place); something
must happen to induce transcription, or turn it on. Transcription is turned on when a small
molecule called an inducer binds to the repressor
Inducible operons
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s are those in which transcription is normally on (taking place); something
must happen to repress transcription, or turn it off. To turn transcription off, a small molecule
called a corepressor binds to the repressor and makes it capable of binding to the operator.
Repressible operons
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helps to control the expression of the structural genes of the operon by
increasing or decreasing their transcription. Although it affects operon function, it is not
considered part of the operon.
Regulator gene
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Two types of transcriptional control
Negative control, in which a regulatory protein is a repressor, binding to DNA and inhibiting
transcription
* Positive control- in which a regulatory protein is an activator, stimulating transcription
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Gene regulation in eukaryotic cells takes place in multiple levels
* Changes in Chromatin Structure
. For a gene to be
transcribed, proteins called ------------------ must bind to the DNA. Other regulator
proteins and RNA polymerase must also bind to the DNA for transcription to take place.
transcription factors
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Some transcription factors and other regulatory proteins alter chromatin structure
without altering the chemical structure of the histones directly
1. Chromatin remodeling
77
Affects gene expression by altering chromatin structure directly or, in some cases, by
providing recognition sites for proteins that bind to DNA and then regulate transcription
Histone modification
78
The addition of methyl groups to the tails of histone proteins can bring about either the
activation or the repression of transcription, depending on which histone is modified,
which particular amino acids in the tails are methylated, and how many methyl groups
are added
Methylation of histones
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Acetylation of histones usually stimulates transcription
Acetylation of histones
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Heavily methylated DNA is associated with the repression of transcription in vertebrates
and plants, whereas transcriptionally active DNA is usually unmethylated in these
organisms.
DNA methylation
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* Transcriptional Regulator Proteins
enhancers
repressor or silencer
insulators
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- required to bring about normal levels of transcription; may be located some
distance from the gene; might recruit RNA polymerase, which might then be transferred
to the promoter when the enhancer interacts with the promoter
enhancer
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regulatory proteins in eukaryotic cells that inhibit transcription.
Repressor or silencer
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DNA sequences that block or insulate the
effects of enhancers in a position-dependent manner. If the insulator lies between the
enhancer and the promoter, it blocks the action of the enhancer, but if the insulator lies
outside the region between the two, it has no effect
Insulators (also called boundary elements)-
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RNA Interference and Gene Regulation
RNA cleavage
* Inhibition of translation
* Transcriptional silencing
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may play a role in the regulation of gene
expression
Posttranslational Modification of Proteins
