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A mutation that increases the affinity for GTP and a mutation that results in an increase associated with guanine exchange factors are
more active
A mutation that increases the GTPase activity and a mutation that increases the affinity for GDP are
less active
A disulfide bond is a
covalent interaction within the protein
What is true of prion proteins?
they are misfolded forms of normal proteins
they can spread from one organism to another
What is NOT true of prion proteins?
they cannot spread from cell to cell
they form unstable protein aggregates
In an alpha helix, hydrogen bonds form between what?
every fourth amino acid
Protein molecules that have a quaternary structure must have two or more of what?
polypeptide chains
What is the definition of a protein-binding site?
any region on a proteins surface that interacts with another molecule through noncovalent bonding
What does the primary structure of a protein refer to?
the linear amino acid sequence of the protein
What do the segments of a transmembrane protein that cross the lipid bilayer usually consist of?
an alpha helix with mostly nonpolar side chains
Generally speaking, what determines the biological activity of a protein?
amino acid sequence
Which part of an amino acid gives it its unique properties?
side chain
What parts of amino acids are involved in a peptide bond?
amino group of one amino acid and side chain of another
Which amino acid is involved in the formation of disulfide bonds?
cysteine
What would happen to the secondary structure of a protein if an alcohol that disrupts hydrogen-bonding were added
the beta sheets would unfold, disrupting protein structure
the alpha helices would unfold, disrupting protein structure
Both alpha helices and beta sheets:
formed by hydrogen-bonding between backbone atoms
can be formed by many sequences
Beta sheets only:
side chains alternating above and below the structure
consists of antiparallel or parallel strands
Alpha helices only:
cylindrical structure
one full turn every 3.6 amino acids
In a cytosolic folded protein, what orientation and/or interaction do the hydrophobic amino acids tend to have?
theyre tucked away inside the protein
theyre interacting with other nonpolar amino acids
Enzymes can have both active and regulatory sites. What is the purpose of these sites?
the binding of CTP at a regulatory site on the protein causes decreased production of carbamoyl aspartate
Ras is a
GTP-binding protein involved in cell division (proliferation)
Ras activates
cell signaling pathways that promote cell division
Mutations in the gene that encodes Ras can lead to
cancer
How might mutations in the gene encoding Ras lead to the uncontrolled proliferation characteristic of cancer cells?
they decrease the rate at which Ras hydrolyzes GTP
How does the GTP bound form of a GTP-binding protein switch to a GDP-bound form?
it hydrolyzes GTP, releasing a phosphate
Many proteins are regulated by the binding of
GTP or GDP
Which form is the active state of a protein?
the GTP-bound form
Phosphorylation is the only form of covalent modification that can affect a protein’s activity or location. True or false?
false
Phosphorylation can only take place in the cell nucleus. True or false?
false
The formation of an alpha helix is governed by
hydrogen bonding between atoms that are not in the side chains
What level of protein structure involved the interaction of more than one polypeptide chain into a 3-D structure?
quaternary
A binding site on the surface of a protein interacts specifically with another protein through
many weak noncovalent interactions
Disulfide bonds stabilize protein shape outside the cell by
covalent bonds between cysteines
The function of feedback inhibition of an enzymatic pathway is to
turn off synthesis of a product when it is in abundance
When a ligan binds to an allosteric enzyme’s regulatory site, it changes the activity of that enzyme by
inducing a conformational change
How does phosphorylation of a protein affect its activity?
could increase or decrease activity
How does binding of GTP to a GTP-binding protein affect its activity?
always activates the protein
Chemical modifications like phosphorylation and acetylation of proteins occur on
side chains of amino acids and can affect interaction of proteins with other cell components or structures
Unsequenced DNA is likely part of
euchromatin
Centromeric DNA is likely to be
sequenced in all samples
Which chemical group is at the 3’ end of a DNA strand?
hydroxyl group
Prokaryotes have chromosomes that are
circular in structure
Prokaryotic chromosomes would lack
telomeres, centromeres, and a nucleus
The majority of human DNA does not code for genes. True or false?
true
What histone protein is thought to act as a linker that pulls nucleosomes together into a regular repearing array, resulting in 30nm fiber?
H1
Because nucleosomes play a key role in packaging DNA into chromosomes, they bind to the DNA molecule very tightly, and once they’re assembled, they cannot be moved. True or false?
false
Histone proteins have a high proportion of
positively charged amino acids, which bind tightly to the negatively charged DNA backbone
Nucleosomes are found only in mitotic chromosomes. True or false?
false
Nucleosomes represent the
first and most fundamental level of chromatin packing
Nucleosomes can be seen in
the electron microscope
A nucleosome consists of
DNA wrapped around 8 histone proteins, plus a short segment of linker DNA
Nucleosomes convert a DNA molecule into a
chromatin thread about 1/3 length of the intial DNA
What structure in an interphase eukaryotic cell is the site of ribosomal RNA transcription?
nucleolus
Telomeres cap the ends of
linear chromosomes and prevent them from being recognized by the cell as broken DNA in need of repair
Telomeres contain
repeated nucleotide sequences that are required to replicate the ends of linear chromosomes
What represents the specializede DNA sequence that attaches to microtubules and allows duplicated eukaryotic chromosomes to be separated during M phase?
centromere
What suggests that the large amount of excess “junk” DNA in a genome may serve an important function?
a portion of “junk” DNA is highly conserved in its DNA sequence among many different eukaryotic species
Duplicated chromosomes are
separated during mitosis of the cell cycle
What alteration would prevent proper chromosome segregation during mitosis?
deletion of the centromere sequence
How do chromatin-remodeling complexes work?
they use energy from ATP hydrolysis to alter the arrangement of nucleosomes, rendering certain regions of the DNA more accessible to other proteins
The tails of the core histone protein can be chemically modified by the covalent addition of
acetyl groups
methyl groups
phosphate groups
What is the name given to the most highly condensed form of chromatin?
heterochromatin
When a cell divides, its chromatin structure is completely reset. True or false?
false
Once heterochromatin has been established, it will often spread until it encounters what?
a barrier DNA sequence
Histone tail modifications establish and maintain the different chromatin structures found in heterochromatin and euchromatin. True or false?
true
Chromatin-remodeling complex uses ATP energy to alter chromatin:
may increase or decrease transcription
Histone acetyltransferase adds acetyl groups to histone tails:
increase transcription
Histone deacetylase removes acetyl groups from histone tails:
decrease transcription
Methyltransferases add methyl groups to histone tails:
may increase or decrease transcription
What is a function of the protein component of chromosomes?
it packages the DNA strands
What is the relationship between genome size and organismal complexity?
more complex organisms generally have larger genomes but there are many notable exceptions
Portions of junk sequence DNA are conserved between species and thus may be functional. True or false?
true
What specialized DNA sequences provides an attachment point for the segregation of duplicated chromosomes?
centromeres
What is a function of the nucleolus?
to assemble ribosomal RNA and proteins into ribosomes
How does methylation of histone tails affect the accessibility of DNA?
it can have different effects depending on the location
What region most likely contains the highest density of genes?
euchromatin
What can happen if heterochromatin spreads inappropriately into an area with active genes?
the active genes can become silenced
The double helix in each daughter cell consists of
one parental strand and one newly synthesized strand
What best describes DNA replication?
semiconservative
What kinds of bonds link the two strands of a double helix to each other?
hydrogen
Nucleotides in each strand of DNA are held together by what type of bonds?
phosphodiester
Approximately how often does DNA polymerase make an error during DNA replication?
once per 10 million nucleotides added to the growing DNA chain
When does DNA polymerase perform its editing function on incorrectly incorporated nucleotides?
before adding the next nucleotide in the chain
The error-correcting proofreading activity of DNA polymerase occurs in which direction?
opposite the direction of polymerization
What does depurination refer to?
the loss of A or G bases from DNA
How does ultraviolet radiation in sunlight typically damage DNA?
it causes two adjacent pyrimidine bases to become covalently linked
What type of enzyme removes damaged DNA from the rest of the DNA molecule?
polymerase
In the absence of repair, what would the replication of a double helix containing a mismatch yield?
one DNA molecule with the normal sequence and one DNA molecule with a mutated sequence
What occurs when a cell repairs a double-strand DNA break by the process of nonhomologous end joining?
the DNA sequence at the site of repair is altered by a short deletion
Double-strand breaks can be repaired flawlessly by what?
homologous recombination
The DNA sequence at the site of repair contains a short segment of telomere DNA. True or false?
false