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218 Cards in this Set

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how DNA is replicated?
This is the semi-conservative model of replication; each strand serves as a template for the synthesis of the new DNA.
Why are the results of studies on E. coli DNA replication applicable to the same process in humans?
E. coli is similar to humans because it replicates its entire genome before every cell division. Note: E. coli has a circular chromosome, which is very different from chromosome structure in humans.
What is the primary function of DNA polymerase I (Pol I)?
repairs damaged DNA
Replication
is primarily conducted by DNA polymerase III.
Synthesis
goes from the 5’ to the 3’ end of the molecule being synthesized (other direction).
DNA polymerase III
adds nucleotides to the lagging strand.
Ligase
closes the gaps between Okazaki fragments.
DNA polymerase I
is involved in repairing damaged DNA.
Which of the following best describes the structure of a DNA molecule?
a sugar-phosphate backbone with adenine, thymine, guanine, and cytosine bases projecting towards the inside of the backbone
The correct order of events as they occur in the process of DNA replication?
helicase opens helix, Pol III elongates primer and synthesizes leading and lagging strands, DNA ligase links fragments of DNA
Which of the following is an important consideration if you are attempting to amplify a gene using PCR:
finding primers that are complementary to both the 3’ to 5’ and the 5’ to 3’ regions to either side of the gene of interest NOte: “Identical” primers will not bind.
A researcher has discovered a mutant E. coli strain that grows well at very low temperatures (around 10 degrees C), but not at higher temperatures. If this strain were compared to “normal” E. coli cells grown at 37 degrees C, which of the following would most likely be found in the “cold” mutant, but not in the “normal” strain?
a DNA synthesis enzyme that is only functional at cold temperatures If DNA synthesis does not occur at higher temperatures, the cells will not be able to grow.
Cancer can occur when DNA is damaged. Which of the following statements is true regarding the cause of damage to DNA molecules?
DNA molecules can break down in the absence of environmental toxins or radiation. Although enzymes minimize the damage done to DNA, they do not correct all of the mistakes. Some mutations that are not corrected lead to cancer.
Imagine that you are a researcher working on developing a gene therapy for XP patients. Which of the following would be the best “gene” to incorporate into the skin cells of these patients, based in the data shown in the figure?
a gene that would increase the production of DNA polymerase I
What comprises an individual’s genome?
all of its mRNAS
What is the most general definition of a mutation?
any change in an individual’s genome
Where and how are Okazaki fragments synthesized?
at the lagging strand, oriented in a 5'to 3' direction
How do dideoxyribonucleotides (ddNTPs) and deoxyribonucleotides (dNTPs) compare?
ddNTPs lack a hydroxyl (OH) group on their 2' and 3' carbons.
Translation
Translation of mRNA to protein occurs within the cytoplasm of a eukaryotic cell.
Where are the DNA polymerase enzymes synthesized in a eukaryotic cell?
in the cytoplasm, on ribosomes
Transcription normally stops when
the RNA polymerase reaches a stop codon on the DNA.
Which of the following statements is true regarding transcription in bacteria and eukaryotes?
Bacteria and eukaryotes rely on proteins that recognize specific DNA sequences to initiate transcription.
Which of the following is an advantage (relative to bacteria) of the way transcription occurs in eukaryotes?
The compartmentalization of the cell allows for a large amount of post-transcriptional modifications of the proteins.
Which of the following are required as an energy source for translation?
GTP and ATP
How did the A-site of the ribosome get its name?
It is the site occupied by incoming aminoacyl tRNAs.
How did the P-site of the ribosome get its name?
It is where peptidyl tRNAs reside.
What is a molecular chaperone?
a protein that helps newly translated proteins fold into their proper 3-D configuration
Some plants are triploid. If a plant has a chromosome number of 42, how many chromosomes are present in its somatic cells?
126
When a sperm and egg combine, the resulting embryo has
half of the mother’s genetic information and half of the father’s.
If a cell has a diploid number of 50, how many chromosomes are present in the nucleus at the beginning of meiosis? How many chromosomes are present in each resulting cell at the end of meiosis?
beginning – 50, end – 25
The cells that produce sperm in humans contain 46 chromosomes. If one of these cells undergoes meiosis to form sperm cells, and chromosomal nondisjunction occurs in chromosome 22 during meiosis I, what is the chromosome number in each of the resulting sperm?
24; 24; 22; 22
The cells that produce sperm in humans contain 46 chromosomes. If one of these cells undergoes meiosis to form sperm cells, and chromosomal nondisjunction occurs in chromosome 22 during meiosis II, what is the chromosome number in each of the resulting sperm?
23; 23; 22; 24
Which of the following occurs during meiosis II, but does NOT occur as part of meiosis I?
separation of sister chromatids
crossing over between homologous chromosomes
This occurs during prophase I.
crossing-over points
chiasmata
An individual plant that exhibits self-fertilization can produce offspring different from itself primarily as the result of:
independent assortment and crossing over during the formation of gametes
What is a tetrad?
a group of four sister chromatids
Meiosis II is similar to what process?
mitosis in haploid cells
What is genetic recombination?
the combination of a prominent haploid phase and a prominent diploid phase in a life cycle
What is a model organism?
an organism that is used to study a scientific question, in which the results have applications to other species
Homologous chromosomes/homologs:
chromosomes that define the same set of traits,and have the same size and shape
Gene:
a section of DNA that codes for a trait.
Allele:
different versions of genes.
Diploid
a full set of homologous chromosomes, found in body cells (= autosomal cells).
Polyploid:
more than one full set of homologous chromosomes.
Sister chromatids:
half of a replicated chromosome, joined to its sister chromatid by a nonreplicated portion of DNA (= Centromere).
Synaptonemal complex:
proteins that join homologous chromosomes, so that crossing over occurs between non-sister chromatids.
Genetic recombination:
the result of crossing over; the production of new combination of alleles
Nondisjunction:
when homologous chromosomes do not separate during meiosis.
Trait
A characteristic of an individual or an allele. (i.e. brown hair versus blond hair).
Phenotype
Observable traits of an individual, the expressed form of genes.
Hybrids
A mix of two parental types.
Parental generation:
Adults used in the initial cross, often a pure line.
F1 generation:
The offspring of the parental generation = first filial generation.
Recessive trait:
A trait that is only expressed when an individual possess two alleles of that trait
Dominant trait:
A trait that is expressed when present as a single copy/allele in an individual
Homozygous
The genotype that has two copies of the same allele (i.e. AA or aa).
Heterozygous
The genotype that has different copies of alleles for a gene (i.e. Aa).
Wild type:
Individuals with the most common phenotype.
Mutants
phenotype differing from the most common phenotype, usually caused by a genetic abnormality ( = mutation).
Autosomal traits:
Genes carried on non-sex chromosomes.
Sex-linked traits:
Genes carried on sex chromosomes, usually associated with the X chromosome
Recombinant
Individuals with phenotypes resulting from the crossing over of alleles on chromosomes
Discrete traits:
Traits that are discontinuous in variation. (i.e. white or black fur).
Quantitative traits:
Traits that vary continuously in a range (i.e. height, weight).
The Principle of Segregation:
Each gamete contains one allele of each gene
The Principle of Independent Assortment:
Alleles of different genes sort into gametes independently of other genes
The Chromosome Theory of Inheritance:
Genes are located on chromosomes which are passed on through gametes from parent to offspring.
Strain
genetically identical individuals, such as viruses or bacteria.
Virulence
the ability to cause disease; i.e. fatal, non-lethal.
DNA
the genetic material; deoxyribonucleic acid.
RNA:
single stranded, short pieces of nucleotides, ribonucleic acid.
Double helix:
the structure of DNA; the sugar phosphate backbone on the outside as the ladders’ sides, the nitrogen containing bases as the rungs of a ladder.
Semiconservative replication:
a new DNA molecule contains one side of original DNA one strand of novel DNA, facilitated by base pairing.
dNTP's:
the individual nitrogen-containing base (A, C, G, T), the ribose ring, and the three phosphates.
DNA polymerase:
an enzyme that adds dNTP’s to the 3’ position on the ribose ring.
Primer
a short piece of RNA that binds to DNA, signaling the DNA polymerase to begin replication.
Origin of replication:
in a bacterium, the beginning of replication in the circular genome.
Replication fork:
a Y-shaped region in eukaryotic organisms where DNA unravels to allow replication.
Helicase
an enzyme that breaks hydrogen bonds between the “rungs” of bases, allowing DNA to unwind.
Single strand DNA binding proteins:
proteins that keep the DNA from “zipping” back up.
Topisomerases
an enzyme that cuts DNA downstream from the replication fork and reconnects it to avoid twists and knots in the DNA.
Primase
an enzyme that makes primers from RNA.
Sliding clamp:
a protein that follows the DNA polymerase, holding it in place.
Leading strand:
the DNA strand that runs 5’-3’; it is replicated in one continuous piece.
Lagging strand:
complimentary to the leading strand, running 3’-5’. It is replicated in shorter pieces, 1000 bp, discontinuously.
Okazaki fragments:
short pieces of DNA added to the lagging strand.
DNA Ligase:
an enzyme that joins the sugar phosphate backbone of the Okazaki fragments.
Telomere
the linear end of a chromosome, usually made of junk DNA.
Telomerase
an enzyme that has an RNA template and replicates the ends of chromosomes.
Mismatch repair:
the process of proofreading enzymes repairing mistakes in base pairing of DNA
Methylation
The template DNA has methyl groups attached to it, allowing the proofreading enzymes to distinguish the mistake from the template.
Excision repair systems:
enzymes that cut out regions of damaged DNA.
Metabolic pathway:
a series of steps in which a chemical is broken down by a succession of enzymes (proteins) to make smaller molecules and energy that is used for growth.
One gene, one enzyme hypothesis:
each gene is responsible for making one protein/enzyme.
Knock-out, null, or loss of function mutants:
an allele that has been altered so that it cannot produce an enzyme.
Genetic screen:
using media with nutritional supplements to select particular strains of the model organism.
mRNA
Messenger RNA, molecules of RNA that carry the genetic code from the DNA in the nucleus to the cytoplasm to produce a protein.
Genetic code:
sequences of DNA that produce amino acid chains (= proteins/enzymes).
Triplet code:
Three letters of DNA that code for a particular amino acid.
Redundant:
Each amino acid is coded by several types of triplets.
Codon:
A group of three bases that codes for an amino acid.
Reading frame:
The sequence of codons that make a protein.
Start codon:
A sequence of three bases that tells the trascriptase enzyme where to start (AUG = methionine). It is the same for all life.
Stop codon:
A sequence of three bases that ends the chain of amino acids; it does not code for an amino acid.
The Central Dogma:
The theory that summarizes the flow of information in cells. DNA > RNA > Protein
Transcription:
use of a DNA template to make mRNA.
Translation:
use of mRNA to make protein.
Template strand (= sense strand):
The DNA (3’ to 5’) that is read by RNA polymerase to make mRNA.
Non-template strand (= antisense strand):
DNA that is not used to make mRNA (5’ to 3’),
Sigma
a subunit of the RNA polymerase that allows transcription to begin in prokaryotes.
Holoenzyme
the sigma + core enzyme of RNA polymerase.
Promoters
segments of DNA that bind the sigma subunit to begin transcription (-10 box, and –35 box in prokaryotes).
Upstream
before the template strand start.
Downstream
after the template strand start.
Basal transcription factors:
the equivalent of the sigma in eukaryotes.
Exons
coding pieces of DNA/mRNA.
Introns
non-coding pieces of DNA/mRNA that are spliced out of mRNA.
Splicing
the process of removing introns from the mRNA.
snRNP's
enzymes that cut out introns from mRNA.
Spliceosome:
the complex formed by the snRNP’s and the intron, lariat shaped.
Wobble hypothesis:
the third position of the tRNA anticodon can be variable and loosely match the mRNA.
Shine-Delgarno site:
the sequence of mRNA that binds to the ribosome to begin translation.
Polyribosomes:
Many ribosomes translating the same piece of mRNA.
Mutation
any change in an organism’s DNA.
Point mutation:
a simple mismatched base in DNA or mRNA.
Missense or replacement mutations:
point mutations that change the amino acid sequence (i.e. sickle cell aenemia).
Deleterious mutation:
a mutation that harms the individual.
Silent mutation:
a mutation that has no effect on the individual (said to be neutral, not positive or negative).
Chromosome inversion:
mutations caused when the chromosome breaks and rejoins in a novel way.
meiotic events in the correct order.
Crossing over occurs, the chromosomes line up in the middle of the cell, the spindle fiber separates the sister chromosomes
The genotype AA can also be expressed as:
Homozygous dominant
Ligase is used to:
Cap off the ends of cleaved DNA
prokaryotic gene expression?
Prokaryotic mRNA’s are often translated before transcription is complete.
What was significant about the protein work on sickle cell anemia by Ingram?
A change in one amino acid can affect a protein’s structure.
A genetic map can be used to determine:
The relative position of alleles on chromosomes.
An organism with 8 chromosomes in somatic tissue will have ___ in sex cells.
4
The appearance resulting from a given gene combination is referred to as:
Phenotype
In DNA guanine always pairs with
Cytosine
Together with proteins rRNA provides a site for…
polypeptide synthesis
A procedure called PCR is used to
Copy gene sequences
Enhancers are
Distant sites where regulatory proteins bind
The role of methylation of DNA is now viewed as:
Insuring that genes that are turned off stay turned off
As polypeptides are formed at the ribosome, elongation continues until ___ is exposed.
c. A stop codon
DNA replication is called semiconservative because ____ of the original duplex appears in the new duplex.
Half
______, a disease caused by a dominant gene, is often passed on because its effect is delayed until bout the age of thirty years.
Huntington’s disease
Sexual reproduction favors
Genetic diversity
Homologous chromosomes separate, sister chromatids remain together during:
Anaphase I
Continuous variation
is observed in traits like height, are controlled by multiple genes, are called quantative traits
Using mice and pneumonia bacteria, Griffith found
That genetic material could pass between killed bacteria and harmless bacteria
The template strand is:
copied during transcription, complementary to the coding strand, complementary to the transcribed mRNA
Operons are
In prokaryotic cells
When the mRNA leaves the cell’s nucleus, it next becomes associated with:
A ribosome
Okazaki fragments are
Found on the lagging strand
Mitosis results in two ____ cells, while meiosis results in ____ haploid cells.
Diploid/four
Chromosomes condense tightly in
Prophase I
The ratio often referred to as the Mendelian ratio is:
3 to 1
In prokaryotic transcription, the –35 sequence and the –10 sequence are
Promoters
_____ tend to cause RNA’s to be degraded between transcription and translation.
siRNA's
In order for a gene to be transcribed, RNA polymerase must have access to the DNA helix and be able to bind the gene’s
On which of the chromosomes is the sex-linked gene carried?
X
Unique to meiosis is the failure of chromosomes to replicate between
Telophase I and prophase II
The sister chromatids are connected at the
Centromere
The Y chromosome in males comes from his ____; his X comes from his ______.
Father/mother
When DNA replicates semiconservatively, which of the following is true of each daughter DNA molecule?
One strand is newly synthesized, whereas the other strand is a strand from the parent DNA molecule.
With respect to human height, the production of short individuals by two average sized parents is best explained by
polygenic inheritance
An important evolutionary benefit of sexual reproduction is that
it provides a mechanism for genetic recombination
____ carries an anticodon and a specific amino acid to a growing polypeptide chain.
tRNA
A key difference between mitosis and meiosis is:
synapsis of homologous chromosomes in meiosis
Genetic variation, provided through sexual reproduction, offers more opportunity for offspring to survive in changing environments. What two aspects of meiosis provide sources of such variation?
crossing over and independent assortment of chromosomes
In the 1950s, Hershey and Chase conducted a now famous experiment to determine whether DNA or protein carried the hereditary information in virus T2. What method did they used to “tag” the DNA and protein constituents of T2?
35S to tag the protein and 32P to tag the DNA
Double-stranded nucleic acids are said to be antiparallel. What structural configuration is antiparallel?
The C-5′ to C-3′ ribose orientations run in opposite directions on the complementary strands.
At the ends of chromosomes in eukaryotes, a problem exists with repeated DNA replication on the __________ strand. A __________ enzyme is responsible for providing a solution to this problem.
lagging; telomerase
Crick and co-workers found that when three base additions or three base deletions occurred in a single gene, the wild-type phenotype was sometimes restored. These data indicated:
The code is triplet.
DNA> DNA
replication
DNA>RNA
transcription
RNA>Protein
Translation
A significant experiment was conducted in which a scientist placed RNA polymerasesigma factors in a tube containing T7 viral DNA. He then added DNase to the tube to digest unprotected DNA, followed by a chemical that degrades proteins. He was left with a stretch of DNA that would most likely be:
promoters
A nonsense mutation is one in which:
The mutant protein is shorter than normal.
Although the expression of most genes is tightly regulated, some genes are expressed at roughly constant rates (i.e., constitutively). Which of the following genes would you predict to be constitutively expressed?
genes that that code for ribosomal RNAs
A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first child will be an albino?
1 of 4
When Mendel crossed smooth yellow seeds with wrinkled green seeds, the F1 seeds were smooth and yellow. When he allowed these plants to self fertilize, what ratio of phenotypes did he see?
9 . 3. 3. 1
Independent assortment occurs because of:
chromosomes line up randomly at metaphase.
A man who carries an X-linked allele (gene) will pass it on to
all of his daughters
Marfan syndrome, a condition that Abraham Lincoln had, is a condition that causes enlarged stature, back deformities, and heart problems. The allele that causes this condition is said to be
pleiotropic
One example of a quantitative trait is:
height
DNA replicates in a semi-conservative manner, meaning:
each new strand of DNA has one side of the original strand.
DNA polymerase can only work if there is an overhang on the DNA template’s 5’ end. An enzyme called _____ adds RNA to make this overhang.
primase
Telomerase is a specialized enzyme dealing with the lagging strand in ______ cells.
gamete
People that have XP:
lack mismatch repair enzymes that fix damage from UV light.
Mismatch repair enzymes identify template strands from the new strands (that have mistakes) by:
methylation on the template strand.
The discontinuous aspect of DNA replication that occurs on the lagging strand is caused by: the 5’ to 3’ polarity restriction
According to the central dogma, DNA is for ______, RNA is for _______.
storage; carrying information.
What three components make up a nucleotide?
sugar, phosphate, nitrogenous base
During DNA replication, DNA ligase is most active on the lagging strand. This is because:
The lagging strands contain more short DNA segments than the leading strand, and these short segments are ligated together by DNA ligase.
Beadle and Tatum proposed, in its original form, the one-gene, one-enzyme concept. In more modern terms, this hypothesis could be restated in which of the following ways?
A given sequence of DNA nucleotides contains the information to make one enzyme
When examining the genetic code, it is apparent that:
There can be more than one codon for a particular amino acid.
In Eukaryotes, mRNA is completely processed:
when splicing is finished, and the 5’cap and the poly A tail are added.
Translation ends when:
the release factor enters the A site.
In sickle cell anemia, the mutated hemoglobin has a valine amino acid instead of a glutamic acid amino acid. This type of mutation is called a ______.
missense/replacement mutation
Given there are three stop codons that do not code for a given amino acid, you might expect there would be 61 tRNAs. But the actual number is smaller (about 40), because:
Some tRNAs have anticodons that can recognize two or more different codons by wobling
When Mendel crossed two pea plants that were heterozygous for smooth versus wrinkled, he found:
Three smooth, one wrinkled.
How do you know if you have two genes that sort independently, if you cross two heterozygous parents for those genes?
You get novel phenotypes.
What causes independent assortment?
Sister chromosomes randomly lining up during Metaphase I
When Griffith injected mice with the four strains of Streptococcus pneumoniae (R = benign, S = lethal), he found:
Mice died when injected with R strain and heat-killed S strain.
Hershey and Chase used radiolabelling and viruses to examine what provided genetic information to cells, proteins or DNA. What result led them to this conclusion?
Radioactive DNA was found in the pellet with the bacterial genes.
DNA was proven to replicate semiconservatively. This conclusion was reached by using radioactive nitrogen, and by observing DNA after two generations of replication. After two generations, researchers saw:
An intermediate density band and a low density band.
Which of these happens first in DNA replication?
The helicase unwinds the DNA.
How long is a codon?
Three bases
DNA makes _____ that then makes _____.
RNA; protein
When we say that the genetic code is redundant, we mean that:
One amino acid is coded by several codons.
Which of the following mutations would have the greatest negative impact on the protein product of a gene?
a single base insertion near the start of the coding region of the gene
Messenger RNA (mRNA) is constructed in:
the 3’ direction.
The sigma factor binds to:
The –10 and –35 boxes.
In Eukaryotes ____ are coding areas; ____ are spliced out of mRNA.
exons; introns
In _____ transcription and translation occurs simultaneously.
Prokaryotes
When researchers labeled amino acids with radioactive sulphur, they found that over time, radioactivity in tRNA:
decreased.
The area of tRNA that binds to mRNA is called:
the anticodon