Midterm 2 Flashcards
The term that describes the highly compacted regions of chromosomes observed during interphase is
heterochromatin
When Avery, MacLeod, and McCarty added RNase and protease to their DNA extracts, what happened?
The R strain was converted to the S strain.
Following semiconservative DNA replication, what are the compositions of the two double helices that are made?
Both double helices contain one original DNA strand and one new strand.
The location on the DNA where transcription begins is called
promotor
a collection of 64 codons that either specify amino acids or function to stop translation
“genetic code”
The two strands of a double-stranded DNA molecule are held together by
hydrogen bonds.
An organized unit of DNA sequences that enables a segment of DNA to be transcribed into RNA, and ultimately results in the formation of a functional product, is called a
gene
DNA replication begins at special sites on the parental DNA molecule known as
origin(s) of replication
A new DNA strand elongates only in the 5’ to 3’ direction because…
DNA polymerase can only add nucleotides to the free 3’ end.
The site where translation takes place is the
ribosome
Which of the enzymes synthesizes short segments of RNA?
DNA primase.
The regions within an mRNA that are removed during splicing are called
introns
Which of the following molecules is a regulatory transcription factor? Operon. Inducer. Promoter. Repressor.
repressor
Modification of DNA by the covalent attachment of methyl groups usually
silences gene expression.
Which of the following activities is not catalyzed by chromatin-remodeling complexes?
Change the positions of nucleosomes.
Evict histones from the DNA.
Degrade histone proteins.
Replace standard histones with variant histones.
Degrade histone proteins.
A protein that binds to the DNA and stimulates transcription is called
an activator.
How does having glucose in the environment inhibit transcription of the lac operon?
By reducing the levels of cAMP produced in the cell.
With regard to transcriptional regulation in eukaryotic cells, it has been shown that many genes are regulated by multiple factors. This phenomenon is referred to as
Combinatorial control.
in positive control of the lac operon, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. Which of the following environmental conditions causes an increase in CAP activity in stimulating transcription?
An increase in glucose.
A decrease in glucose and an increase in cAMP.
An increase in glucose and a decrease in cAMP.
A decrease in cAMP.
A decrease in glucose and an increase in cAMP.
Cell differentiation occurs because each cell
contains the same set of chromosomes, but their genes are regulated differently.
DNA segments that function to increase transcription levels in eukaryotes are called
enhancers.
How does active CAP induce expression of the genes of the lactose operon?
It terminates production of repressor molecules.
It degrades the substrate allolactose.
It stimulates splicing of the encoded genes.
It stimulates the binding of RNA polymerase to the promoter.
It stimulates the binding of RNA polymerase to the promoter.
The effect of allolactose is:
Conformational change in the lac repressor protein, inducing the lac operon.
Which of the following functions are characteristic of general transcription factors in eukaryotes?
They bind to other proteins or to the TATA box.
In bacteria, the regulation of gene expression most commonly occurs at the level of transcription. Gene regulation in bacteria can also occur at the level of
translation.
A unit of DNA that contains multiple structural genes and is under the control of a single promoter is called
operon
Which of the following conditions is most likely to cause the lactose operon to be transcribed?
There is more glucose in the cell than lactose.
There is glucose but no lactose in the cell.
The cAMP level is high and the lactose level is low.
The cyclic AMP and lactose levels are both high within the cell.
The cyclic AMP and lactose levels are both high within the cell.
A mutation prevents allolactose from binding to the lac repressor, but the repressor protein can still bind to the operator site. How would this affect the regulation of the lac operon?
The operon would be turned on both in presence and absence of lactose.
The operon would be turned off both in the presence and absence of lactose.
The operon would be turned on in the presence of lactose but turned off in the absence of lactose.
The operon would be turned off in the presence of lactose but turned on in the absence of lactose.
The operon would be turned on both in presence and absence of lactose.
For eukaryotic genes that can be transcribed, where are nucleosome-free regions (NFRs) found?
At both the beginning and end of genes.
Which of the following is an event of anaphase in mitosis?
The nuclear envelope breaks down.
Crossing over occurs.
Sister chromatids align longitudinally in the center of the cell.
Sister chromatids separate.
Sister chromatids separate.
A human cell containing 22 autosomes and a Y chromosome is
sperm
A student is looking at cells under the microscope. The cells are from an organism that has a diploid number of fourteen. For one particular slide, the cell has seven replicated chromosomes (7 pairs of sister chromatids) aligned at the metaphase plate of the cell. Which of the following statements accurately describes this particular cell?
The cell is in metaphase II of meiosis.
The process of mitotic cell division:
I. results in daughter cells with half the genetic material of the original cell.
II. is important for growth of an organism.
III. results in daughter cells genetically identical to the original cell. I and III only II only I only II and III only
II and III only
Which of the following is the correct order of the phases in mitosis?
Prometaphase, prophase, metaphase, anaphase, telophase
Prophase, prometaphase, metaphase, anaphase, telophase
Anaphase, prometaphase, prophase, metaphase, telophase
Telophase, prometaphase, prophase, metaphase, anaphase
Prophase, prometaphase, metaphase, anaphase, telophase
Which of the following changes in chromosome structure does not affect the total amount of genetic material? Deletion. Duplication. Inversion. polyploidy
Inversion.
Which two types of proteins function to advance the eukaryotic cell through the phases of the cell cycle?
cyclins and cyclin-dependent kinases (cdks)
During the eukaryotic cell cycle, the cell alternates between
interphase and “M” phase
When homologous chromosomes crossover, what occurs?
Two non-sister chromatids of a bivalent break and re-join with their homologs.
The G2 checkpoint of the cell cycle ensures that
the DNA has been properly replicated.
After telophase I of meiosis, the chromosomal makeup of each daughter cell is __________.
haploid, and the chromosomes are each composed of two chromatids.
Crossing over most commonly occurs during
prophase in meiosis I.
Which of the following is a true statement about sexual vs. asexual reproduction?
Asexual reproduction produces only haploid offspring.
Offspring produced by sexual reproduction have twice as many chromosomes as their parents.
In sexual reproduction, individuals transmit half of their nuclear genes to each of their offspring.
In asexual reproduction, offspring are produced by fertilization without meiosis.
In sexual reproduction, individuals transmit half of their nuclear genes to each of their offspring.
A replicated chromosome in eukaryotes is composed of
two sister chromatids held together at the centromere.
a strand of DNA is formed by the
covalent linkage of nucleotides in a linear manner.
nucelotides contain
a phosphate group, a 5C sugar, and a nitrogen containing base.
Linked by covalent bonds between phosphorus and oxygen
phosphodiester linkage
What forms backbone of DNA or RNA
The phosphates and sugar molecules
Purine bases
Adenine and guanine, double ring structure, in both RNA and DNA.
Pyrimidine bases
thymine, uracil, and cytosine, have a single ring structure. (Cytosine in DNA and RNA. thymine in DNA, uracil in RNA)
Base sequences are
complementary
A/T (? H bonds) and G/C (? H bonds)
2, 3
Dna strands serve as a
template for the synthesis of daughter strands.
- DNA backbone of 2 strands farther apart
2. backbone of 2 strands closer together spiral around the double helix.
- Major groove
2. minor groove
Meselson and Stahl Mechanisms for DNA replications:
Semiconservative
Conservative
Dispersive
DNA replication produces DNA molecules with 1 parental strand and 1 newly made daughter strand.
Semiconservative
DNA replication produces 1 double helix with both parental strands and the other with 2 daughter strands
Conservative
DNA replication produces DNA strands in which segments of new DNA are interspersed with the parental DNA.
Dispersive
When is the DNA replication fork made
When DNA helicase unwinds the double helix structure of the DNA.
made continuously, continues to elongate.
Leading strand
made discontinuously, It is synthesized in fragments, the discontinuous replication results in several short segments
Lagging strand
First compacted by wrapping itself around a group of proteins
histones
When cells prepare to divide, chromosomes become more
condensed
2 noncoding RNA
transfer RNA
ribosomal RNA
where transcription begins
Promotor
site in DNA where it ends.
Terminator
sequences that function as sites for the binding of regulatory proteins that affect the rate of transcription.
Regulatory sequences
(needed to make polypeptides during translation)
transfer RNA
(forms part of ribosomes which is where translation occurs)
ribosomal RNA
produces an RNA copy of a gene from DNA.
Transcription
synthesizes a specific polypeptide.
Translation
The main reasons why genes are regulated:
conserves energy; protein encoded by genes will be produced only when needed.
Ensures that genes are expressed in appropriate cell types and in the correct stage of development.
epsilon and zeta globin genes on
Embryonic stage
alpha and gamma globin turned on
fetal stage
beta and alpha globin genes turned on
at birth
in bacteria, gene regulation occurs most commonly at level of
transcription
decreasing transcription rate, negative control
Repressor
increasing transcription rate, positive control
Activator
proteins that bind to regulatory sequences in DNA
regulatory transcription factors
regulatory transcription factors either…
increase or decrease the rate of transcripition
A. The promoter is used to transcribe 3 genes.
B. encodes B galactosidase (catalyzes the breakdown of glucose)
C. encodes lactose permease (transporter)
D. encodes galactoside transacetylase
E. The operator is a regulatory sequence in DNA
A. lacP B. lacZ C. lacY D. lacA E. lacO
provides a binding site for a repressor protein
lacO
regulatory DNA sequence that’s recognized by an activator protein.
CAP site
_ gene encodes the lac repressor (regulates the lac operon)
lacI
What Initiate’s transcription
core promoter (TATA box and transcriptional start site) and regulatory elements
enhancing transcription rate
Enhancers
decreasing transcription rate
Silencers
What are the regulatory elements
enhancers or silencers
accessible to GTFs and RNA polymerase II so that transcription can occur
Open conformation
difficult for transcription
Closed conformation
RNA binding proteins regulate the
translation of specific mRNA’s.
In eukaryotes, DNA is wrapped around proteins to create a
protein-DNA complex called chromatin
RNA modification
1) Alternative splicing
2) Molecules that regulate the life span of mRNAs.
3) Activation or inactivation of protein products.
Alternative splicing allows
a single gene to code for several different products.
What is this called… RNA polymerase cannot access the DNA when it is supercoiled within the nucleus.The DNA near the promoter must be released from tight interactions with proteins before transcription can begin.
Chromatin remodeling
DNA methylation
attachment of methyl groups to cytosine bases
Ways to change the chromatin structure (chromatin-remodeling complexes)…
- Change location of nucleosomes
- Complexes may evict a histone from the DNA
- Replace standard histones with histone variants
DNA methylation occurs
at the CpG islands near promoters
usually inhibits transcription by preventing the binding of activator proteins or promoting the binding of proteins that inhibit translation.
DNA methylation
A. does not alter the amino acid sequence of the polypeptide even though the nucleotide sequence has changed.
B. a base substitution that changes a single amino acid in a polypeptide (may or may not alter protein function).
C. involves the addition or deletion of a number of nucleotides that’s not in a multiple of three; produces a different amino acid sequence.
D. involves a change from a normal codon to a stop codon; causes translation to be terminated earlier than expected, producing a shorter polypeptide.
E. affects only a single base pair within the DNA, can involve the deletion of a single base pair.
F: cells that give rise to gametes, such as egg or sperm cells; affect gametes and can be passed to offspring; transmitted to 1 of the 2 copies of genes.
A.Silent B. Missense C. Frameshift D. Nonsense E. point F.germ line mutation
result from abnormalities in biological processes; larger genes usually are more likely to incur a mutation than smaller ones.
Spontaneous mutations
caused by environmental agents (mutagens) that enter the cell and alter DNA structure.
Induced mutations
physiological events determine whether traits are passed to offspring.
Physiological adaptation hypothesis
genetic variation occurs as a matter of chance.
Random mutation hypothesis
DNA repair systems…
Direct repair, Base excision and nucleotide excision repair, and Mismatch repair
Metastasis occurs=
when tumor cells enter the bloodstream or surrounding body fluids.
Normal gene, if mutated, can become an oncogene.
Proto-oncogenes
Genetic changes that may convert a proto-oncogene to an oncogene…
Missense mutation, Gene amplification, and Chromosomal translocation
Mutation that causes a gene to be overactive, controls uncontrolled cell growth.
Encode proteins that function in signal transduction pathways involved in cell growth.
Oncogenes
At normal, they encode a protein that helps regulate normal cell growth; preventing cancer.
Tumor suppressor genes
When a mutation eliminates its function, uncontrolled cell growth occurs
-Have one or two functions, maintenance of genome integrity or negative regulation of cell division.
Tumor suppressor genes
Bacterial and archaeal genome characteristics
- a single circular chromosome
- have a few thousand different genes; 1 million base pairs as 1 Mb.
- In bacteria, 95% of the genome codes for proteins and has plasmids.
Eukaryotic genome characteristics
- genome located in the nucleus
- found in linear sets of chromosomes
- humans have 23 linear chromosomes (22 autosomes and 1 X or Y).
- Contains large regions of repetitive DNA
- Most DNA does not code for proteins. (98%)
- larger than bacterial genomes in both the number of genes and genome size
Two common features of eukaryotic genomes
repetitive sequences and transposable elements
segments of DNA that are repeated multiple times within a genome. (found in bacterial, eukaryotic, and archaeal genomes)
Repetitive sequences
2 categories of repetitive sequences
moderately and highly repetitive
sequences that are repeated to several thousand times.
Moderately
those that are repeated tens of thousands to millions of times throughout the genome. (relatively short)
Highly
DNA segments that can move throughout the genome.
Transposable elements
a TE moves to a new site in a genome; inherently mobile.
Transposition
elements that move as DNA molecules; both ends have inverted repeats (DNA sequences that are identical but run in opposite directions.)
DNA transposons
enzyme that facilitates transposition
Transposase
moves by an RNA intermediate; only in eukaryotes; may also contain repeated sequences (terminal repeats at each end that facilitate their recognition).
Retrotransposons
Three general life cycle for eukaryotic sexual reproduction:
Diploid dominant species,
Haploid dominant species,
Alternation of Generations
Species alternate between diploid multicellular organisms
sporophytes.
Between haploid multicellular organisms
gametocytes.
A. centromere near center.
B. centromere off center.
C. centromere near 1 end.
D. centromere at the end.
A. Metacentric
B. Submetacentric
C. Acrocentric
D. Telocentric
Banding only occurs in
eukaryotic cells
Each chromosome has a
short arm (top, p) and a long arm (bottom, q)
Individuals of the same species have the
same number and types of chromosomes usually.
3 common ways to identify chromosomes
size, centromere location, and banding patterns.
Chromosomal mutations-
Deletion
Duplication
Simple translocation
Reciprocal translocation
removes a chromosome segment, becomes deficient in genetic material.
Deletion
flips a region to the opposite orientation.
Inversion
moves segment of 1 chromosome to another
Simple translocation
exchanges pieces between 2 dif chromosomes.
Reciprocal translocation
Variations in chromosome # can be categorized by the…
the sets of chromosomes and the # of chromosome within a set.
Have chromosomes that occur in 1 or more complete sets.
Euploid
chromosome # can vary in a phenomenon; alternation in the # of a particular chromosome so that the total # of chromosomes isn’t an e
Aneuploidy
2n +1
Trisomy
2n-1
Monosomy
an event where chromosomes don’t separate properly during cell division; can occur in meiosis 1 or 11, produces haploid cells that have too many or too little chromosomes.
Nondisjunction
Chromosome # in animals:
- In some cases, an abnormality in chromosome # produces an offspring that can survive.
- Sex chromosome abnormalities can occur (XXY, XYY, XXX, X0)
- Human abnormalities in chromosome # are influenced by the age of the parents.
Polyploidy in mammals is usually
lethal
Aneuploidy can result in disorders like
miscarriage
Chromosome # in plants:
- Plants commonly exhibit polyploidy, not lethal but useful.
- Polyploid species in plants are usually larger in size and more robust, traits that are advantageous in the production of food.
Exhibit greater adaptability= withstand harsher environments.
withstand harsher environments.
when 2 individuals of the same species with different characteristics are bred/crossed.
Hybridization
Mendel studied pea plants because…
- Genetic variation
2. self fertilization
General features of an organism=
each character studied was found in 2 discrete forms=
characters, variants (trait)
available in many varieties and characteristics.
Genetic variation
a female gamete is fertilized by a male gamete from the same plant. (male gametes produced in pollen grains and formed in stamens; female gametes are produced in ovules).
Self-fertilization
What was mendels process with the plants?
Remove stamens from purple flowers.
Transfer pollen from stamens of white flowers to the stigma of a purple flower.
The alleles of different genes assort independently of each other during the process that gives rise to gametes (A specific allele for 1 gene may be found in a gamete regardless of which allele for a different gene is found in the same gamete.)
Law of Independent assortment
The 2 alleles of a gene separate from each other during the process that gives rise to gametes so that every gamete receives only one allele.
Law of segregation
Whats the ratio of dominant and recessive?
In F2 generation?
3: 1
9: 3:3:1
Every individual carries 2 genes for a given character and that gene exists in 2 variant forms
alleles
alleles separate into different haploid cells that give rise to gametes.
Segregation
male and female gametes randomly combine with each other.
Fertilization
A cross in which an experiment follows the variants of only 1 character
single factor cross.
Homozygote vs heterozygote
Homozygote=individual that carries identical copies of the same allele (ex. TT or tt)
Heterozygote= carries 2 different alleles of a gene (Tt)
True breeding parents= what generation?
P. offspring is F1 generation
When the true breeding parents differ in a single character, their F1 offspring is
monohybrids.
F1 monohybrid self fertilizes, producing the ? generation.
F2
2 factor cross yields a
9:3:3:1 ratio in F2 generation
genetic composition of an individual
Genotype
prediction of the outcome of a simple genetic cross.
Punnett square
Crossing the true breeding parents produce a
dihybrid offspring.
Independent assortment occurs in…
Segregation occurs in…
metaphase of meiosis 1 and meiosis 1.
The inheritance patterns of traits can be explained by the…
transmission of chromosomes during meiosis and fertilization.
The physical location of a gene on a chromosome=
locus
When a cell prepares to divide, the homologs replicate to produce …
pairs of sister chromatids (each chromatid carries the original homolog (ex. Either T or t).
Homologs segregate into separate cells in …
meiosis 1
Sister chromatids separate during _ to produce _cells.
meiosis 2, 4 haploid
A. presence of Y chromosome causes maleness; males have XY, females have XX.
B. Y chromosome doesnt determine maleness; females are XX and male has either only 1 sex chromosome or XY; sex is determined by its X chromosomes and set of autosomes.
C. the male carries 2 similar chromosomes, male is ZZ and female is ZW.
D.male bee is made from an unfertilized haploid egg; males=haploid and females=diploid.
A. X-Y system in mammals
B. X-0 system in insects
C. Z-W system in birds
D. Haplodiploid system in bees
Temperature can control
sex development.
Is the X or Y chromosome larger…
In humans, the X chromosome is rather large and carries 1000 protein-encoding genes but the Y chromosome is small and carries fewer than 100 protein-encoding genes.
the passage of epigenetic changes from parent to offspring by sperm or eggs.
Epigenetic inheritance
describes the inheritance patterns of genes that segregate and assort independently.
Mendelian Inheritance
Simple mendelian inheritence says…
phenotypic ratios in the offspring conform Mendel’s law.
A. both the pollen and the egg contribute chloroplasts to the offspring.
B. only the pollen contributes these organelles.
A. biparental inheritence
B. parental inhertience
a cross where the sexes and phenotypes are reversed compared to another cross.
Reciprocal cross
Pigmentation of the offspring depends solely on the pigmentation of a female parent…
maternal inheritance;
Most common pattern of mitochondrial transmission in eukaryotes.
In Mendel’s 7 characteristics, the recessive alleles are…
due to rare mutations
mutations that produce recessive alleles are likely to decrease the synthesis of activity in a functional protein
loss of function alleles.
a mutation in a single gene can have many effects on the individual’s phenotype.
Pleiotropy
when a heterozygote that carries 2 different alleles exhibits a phenotype that’s intermediate between those of the homozygous alleles.
Incomplete dominance
When red and white flowered homozygotes are crossed, a pink flower is made
Incomplete dominance
Many genes are found on the X chromosome but not the Y
X-linked genes.
Sex linked genes are found on
1 sex chromosome not on the other.
when 2 genes are close together on the same chromosome they tend to be transmitted as a unit.
Linkage
A. combination of traits hasn’t changed from the P generation.
B. the smaller number of offspring that have a combo of traits NOT found in the P generation
A. Nonrecombinants
B. Recombinants
determines if the genes for body and wing shape are linked
Testcross
A group of genes that usually stay together during meiosis
linkage group
when it occurs between 2 homologous chromosomes they are much more likely to occur between genes farther apart along on a chromosome
Crossover
homologous chromosomes can exchange pieces of
chromosomes and create new combinations of alleles.
the study of mechanisms that lead to changes in gene expression that can be passed from cell to cell and are reversible, but do not involve a change in the sequence of DNA.
Epigenetic change
the inheritance pattern observed for genes that are located outside the cell nucleus, in the mitochondria or chloroplasts.
Extranuclear inheritance
How can enviornmental agents alter gene expression?
Chemicals in diets: can result in epigenetic changes that cause different phenotypes
Environmental agents have been shown to cause epigenetic changes that are associated with human diseases like cancer.
refers to an analogous situation in which a segment of DNA is marked, and that mark is retained and recognized throughout the life of an organism inheriting the marked DNA.
Genomic imprinting
As a result of genomic imprinting, offspring…
either express a maternal or a paternal allele, depending on how a gene is imprinted/marked.
During gamete formation, ___ from one parent is a mechanism to achieve imprinting.
DNA methylation of an allele
During embryonic development in female mammals, 1 of the X chromosomes undergoes an epigenetic change=
X-chromosome inactivation
one of the two copies of the X chromosome in the somatic cell of female mammals is inactivated in…
XCI
The inactivation of 1 X chromosome in females reduces the number of expressed copies of X linked genes from
2 to 1
an equalization of the expression of X-linked genes in male and female mammals.
XCI achieves dosage compensation
XCl in female mammals occurs when
1 X chromosome in every somatic cell is randomly inactivated.
