Exam #3 Flashcards
Which of the following statements concerning DNA is FALSE?
-The structure of DNA can be described as a double helix.
-DNA is a polymer of nucleotides.
- Purines and pyrimidines are complementary.
-The sugar present in DNA is ribose.
The sugar present in DNA is ribose
Hydrogen bonds can form between guanine and ____, and between adenine and ____.
cytosine; thymine
Which of the following nucleotide sequences represents the complement to the DNA strand, 5′-AGATCCG-3′?
3′-TCTAGGC-5′
_____ bonds link the sugar and phosphate groups in the backbone of DNA molecules.
Covalent phosphodiester
According to Chargaff’s rules,
the adenine content in any DNA molecule is always equal to the thymine content
The two molecules that alternate to form the backbone of a polynucleotide chain are
sugar and phosphate.
____, the ends of eukaryotic chromosomes, shorten with every cell division.
Telomeres
The ends of eukaryotic chromosomes can be lengthened by
telomerase
Unlike normal cells, cancerous cells
can maintain telomere length as they divide
What allows each strand of DNA to serve as a template for a new DNA strand during replication?
Complementary base pairing between purines and pyrimidines on opposite strands
Because a newly synthesized DNA molecule contains ____, the replication process is said to be semiconservative.
one parental strand and one new strand
When a mutation occurs during DNA replication, ____ replaces the incorrect nucleotide with the correct one after the mismatched nucleotide has been removed.
DNA polymerase
Which of the following causes the unwinding of the DNA double helix?
DNA helicase
Why does DNA synthesis proceed in a 5′ to 3′ direction?
DNA polymerases can only add nucleotides to the 3′ end of a polynucleotide strand
Primase is the enzyme responsible for
making short strands of RNA at the site of replication initiation.
The DNA strand that is replicated smoothly and continuously is called the
leading strand.
In DNA replication, the lagging strand
is synthesized as a series of Okazaki fragments.
Okazaki fragments are joined together by
DNA ligase.
Adenine and thymine are held together by two hydrogen bonds in a double stranded DNA molecule.
True
Okazaki fragments are complementary to the leading strand of DNA.
False
The molecule that connects a growing polypeptide chain and mRNA is called:
tRNA
The total number of different three-base combinations of the four nucleic acid bases is:
64
RNA is ____ and contains the nitrogenous base ____, which is absent in DNA.
single stranded; uracil
Ribose differs from deoxyribose by having:
an extra hydroxyl group
Initiation of transcription requires:
a promoter sequence
Why is only one strand of DNA transcribed into mRNA?
Because transcribing both DNA strands would produce different amino acid sequences
These noncoding sequences located within coding regions of ____ genes are called ____.
only eukaryotic; introns
During protein synthesis, ribosomes:
attach to the mRNA molecule and travel along its length to produce a polypeptide
Following peptide bond formation between the amino acid in the A site on the ribosome and the growing polypeptide chain, the tRNA in the A site:
moves to the P site of the ribosome
During translocation, the movement of the ribosome repositions the tRNA linked to the growing polypeptide chain to the ____ site, thereby vacating the ____ site for the arrival of a new amino-acyl tRNA.
P; A
One of the mRNA codons specifying the amino acid leucine is 5′-CUA-3′. Its corresponding anticodon is:
3′-GAU-5′
tRNA molecules are able to act as adapters between amino acids and mRNA during translation because:
tRNA can bind to both mRNA and an amino acid.
Translation is initiated at the ____.
AUG codon
A mutation that replaces one amino acid in a protein with another is called a ____ mutation.
missense
A ____ mutation results in the conversion of a codon specifying an amino acid to a termination codon.
nonsense
Frameshift mutations result from the:
insertion or deletion of one or two base pairs
Gene expression in bacteria is regulated primarily by
transcriptional control
An inducible operon is usually controlled by:
an active repressor that keeps it in the “off” state
The organization of the lac operon, from upstream to downstream sequences, is represented by:
promoter -> operator -> lacZ -> lacY -> lac A
Many genes encode proteins that are always needed by a cell, and therefore are always expressed. Such genes are known as:
constitutive
A repressible operon is usually controlled by
an inactive repressor that allows it to be in the “on” state
In the tryptophan operon, the repressor actively binds to the operator when
tryptophan binds to an allosteric site on the repressor protein, thereby activating it
Feedback inhibition is an example of:
posttranslational control
How is enzyme activity regulated by feedback inhibition?
The end product of the metabolic pathway inactivates the first enzyme in the pathway
An operon is defined as:
a group of related structural genes, plus their associated regulatory sequences
In an inducible operon, the ____ is the molecular switch that controls gene expression, while the ____ is the DNA region where RNA polymerase binds to begin transcription.
operator; promoter
Lactose induces the transcription of the lactose operon by:
binding to the allosteric site of the repressor after being converted to allolactose
In Jacob and Monad’s analysis of mutant E. coli strains in their study of the lac operon, the absence of the β-galactosidase enzyme, but presence of the lactose permease and galactosidase transacetylase enzymes, indicated that the mutation occurred in the _____ of the lac operon.
lacZ gene
Inducible genes are usually actively transcribed when:
an inducer inactivates the repressor
Eukaryotic transcription factors:
may be activators or repressors of transcription
_____ is densely staining, highly compacted, and transcriptionally inactive region of chromatin
Heterochromatin
Genes in euchromatic regions are:
transcriptionally active
Methylated DNA sequences typically contain ____ genes.
transcriptionally inactive
Undifferentiated cells that can divide and specialize to form a variety of different cells are called:
stem cells
Cells able to divide and form some types of cells in an organism are called:
pluripotent stem cells
Embryonic stem cells cannot develop into ____ cells.
placental
The only known source of human embryonic stem cells is:
early human embryos
What is a goal of human therapeutic cloning?
to create pluripotent stem cells using a patient’s nucleus
Induced pluripotent stem cells are:
pluripotent cells resulting from reprogramming of differentiated cells
Cloning mammals has proven to be:
a process with a low success rate and a high incidence of genetic defects
Differential gene expression is defined as the:
regulation during development that varies the type and quantity of gene products among cells.
Cells become progressively committed to specific patterns of gene activity and developmental fate through a process known as:
determination
The occurrence of human identical twins is evidence that:
cells in a two-cell human embryo are totipotent.
Due to nuclear equivalence in different cell types, the presence of different cell types in any given organism is accomplished by:
differential gene expression
Totipotent nuclei are capable of:
directing normal development of an organism
For about ____ of mouse genes, there is a similar gene in the human genome.
95%
What evidence supports the idea that some nuclei are totipotent?
Nuclei taken from the cells of an embryonic frog can direct a frog egg to develop into a tadpole.
Evolution is genetic change in ____ that occurs over time.
a population
Overproduction, variation, limits on population growth, and differential reproductive success are all components of:
evolution by natural selection
Four of the following ideas are consistent with Darwinian evolution. Which one is the exception?
Individuals lose characteristics they do not require, or use, and develop characteristics that are useful.
What does the modern synthesis theory of evolution emphasize?
population genetics
Which process provides the genetic variability that natural selection acts on during evolution?
mutation
Individual species will continually evolve as a result of which evolutionary mechanism?
natural selection
What process has been used to produce many of today’s vegetables, such as broccoli, kohlrabi, and cauliflower, which are all derived from wild cabbage?
artificial selection
In which group of islands Charles Darwin observed variation among organisms and compared these organisms to those found on the mainland?
Galapagos Islands
Which are evolutionary modifications that improve the survival and reproductive success of an organism?
adaptations
What is an example of a limit on population growth, and proposed by Darwin to be a mechanism of evolution by natural selection?
predation
The genetic code demonstrates the universality of living things because it is common to virtually all:
organisms
DNA sequencing data suggest that evolutionary changes are related to an accumulation of:
changes in DNA nucleotide sequences
The genetic code is sometimes called “universal,” meaning that all organisms share the same:
coding mechanism
Two species have homologous structures. What can we infer?
The species are related by a common ancestry
Which important finding from the fossil record supports the theory of evolution?
Life has evolved over time.
Where would you most likely find fossilized remains of humans and their immediate ancestors?
only in relatively young rock
Which example best illustrates homoplasy?
bird wings and insect wings
What is the evolutionary relationship between a human arm and a cat’s forelimb?
They are homologous structures.
What is a cladogram?
a diagram showing lines of descent
Which one of the following is NOT an example of evolution through natural selection?
-Antibiotic resistant bacteria
-Different variants of SARS-CoV-2
-Production of many of today’s vegetables, such as broccoli, cauliflower, which are all derived from wild cabbage
-All of the Above
Production of many of today’s vegetables, such as broccoli, cauliflower, which are all derived from wild cabbage
Briefly explain the DNA replication process in few sentences
DNA replication begins when helicase unwinds the DNA double helix, creating two template strands. Primase adds RNA primers so DNA polymerase can build new strands continuously on the leading strand and in short segments called Okazaki fragments on the lagging strand. Ligase connects the Okazaki fragments to complete the strand.
Briefly discuss why the degradation of telomeres result in cellular aging. Conversely, propose why telomere lengthening
could result in cells becoming cancerous.
Telomeres get shorter each time a cell divides, and when they become too short, the cell stops working or dies, causing aging. If telomeres keep getting longer, cells can live too long and divide too much, which can lead to cancer.
Briefly explain the role of methylation and acetylation of histones in regulation of eukaryotic gene expression
Methylation of histones can turn genes off by tightening the DNA around histones, making it harder to read. Acetylation loosens the DNA, making genes easier to access and turn on.
What is the difference between heterochromatin and euchromatin?
Heterochromatin is tightly packed DNA where genes are usually off. Euchromatin is loosely packed, so genes are more active and can be turned on.
Briefly talk about three layers of germs
The three germ layers are ectoderm, mesoderm, and endoderm, and they form during early embryonic development. The ectoderm becomes the skin and nervous system, the mesoderm forms muscles, bones, and the heart, and the endoderm develops into organs like the lungs and digestive system. These layers give rise to all tissues and organs in the body.
What do you know about Induced Pluripotent Stem Cells (iPS cells)? How could iPS cells be used for stem cell research?
Induced pluripotent stem cells (iPS cells) are adult cells that are reprogrammed to act like stem cells. They can be used in research to study diseases, test drugs, and possibly replace damaged tissues without using embryos.
Compare the following terms: homology and homoplasy. Provide two examples of each
Homology occurs when traits are similar because they come from a common ancestor, like the arm bones in humans and bats. Homoplasy happens when traits look similar but evolved separately, like wings in birds and insects.
Give an example of any recent microorganism which has evolved through natural selection from the broad real-world
scenario? Why understanding the mutations and selective pressure that drive that microorganism is important?
A recent example is the evolution of antibiotic-resistant Staphylococcus aureus (MRSA). Understanding the mutations and selective pressures that drive MRSA’s resistance helps us develop better treatments and prevent further spread of resistant infections.
