Molecular Cell Exam 1

Chapters 1,2,4 and 5

Which feature is the distinguishing characteristic that separates eukaryotes from the other domains?

A Nuclear Envelope

All of the following are found in a prokaryotic cell EXCEPT:

A Membrane-Bound Nucleus

Which statement correctly describes the flow of genetic information in all living cells?

DNA is copied by replication, RNA is made by transcription, and protein is made by translation

Which statement about Archaea is correct?

They have unique cell wall chemistry and membrane lipids

Which feature is found in chloroplasts but NOT in mitochondria?

The thylakoid

A cell takes in extracellular material by forming a vesicle at the plasma

membrane. This process is called ________, and the vesicle first fuses with the ______.

endocytosis; endosome

Which observation provides evidence that ribosome function in translation supports the RNA world hypothesis?

Peptide bond formation is catalyzed by peptidyl transferase, an rRNA

of the large subunit

Which sequence correctly orders the evolution of genetic information systems?

Self-replicating RNAs → evolution of RNAs that direct protein synthesis

→ DNA takes over as the genetic material

Match the small organic building block to the macromolecule it forms: Monosaccharide

Polysaccharides/ oligosaccharides (Glycosidic bond)

Match the small organic building block to the macromolecule it forms: Fatty Acids

Fats and membrane lipids (Ester bond)

Match the small organic building block to the macromolecule it forms: Amino Acids

Proteins (Peptide bond)

Match the small organic building block to the macromolecule it forms: Nucleotides

Nucleic acids (Phosphodiester bond)

The bond formed when two monosaccharides are joined by a condensation reaction is a:

Glycosidic Bond

Which of the following is NOT one of the four weak interactions that bring

molecules together in cells?

Covalent Bonds

Which statement about the degree of saturation of fat is correct?

Saturated fats are solid at room temperature and are typically produced

by animals for storage

Which statement about condensation and hydrolysis reactions is correct?

Hydrolysis is energetically favorable; condensation is energetically

unfavorable and requires an input of energy

Peptide bonds joining amino acids are formed by a _____ reaction catalyzed by ____.

dehydration; peptidyl transferase of the ribosome

A nucleotide consists of ________, and the purines are ________.

a nitrogen-containing base, a five-carbon sugar, and 1–3 phosphates;

adenine and guanine

Below is an example of a polypeptide chain. Where on the chain would the

precursor amino acids have formed

Star

The primary structure of a protein is:

Its amino acid sequence

α-helices and β-sheets are produced by:

Hydrogen bonds within the polypeptide backbone

Which statement about protein folding is correct?

Most proteins require chaperone proteins to fold properly

In a protein folded in an AQUEOUS environment:

Nonpolar side chains pack into a hydrophobic core region, while polar

side chains lie on the outside where they can hydrogen-bond to water

Which statement correctly describes the CAUSATIVE AGENT of a TSE?

A misfolded prion protein that binds normal protein and induces

conversion to the abnormal conformation

Which statement about the mechanisms controlling protein activity is

INCORRECT?

Motor proteins move directionally because ATP binding, rather than

ATP hydrolysis, provides the irreversible step in the cycle

A 24-residue segment of a newly sequenced protein has hydrophobic residues at positions 1, 4, 8, 11, 15, 18, and 22. What is the most likely structural role of this segment?

An α helix that either spans a lipid bilayer or wraps around another

helix in a coiled coil

Elastase and chymotrypsin are both serine proteases that cleave peptide bonds by the same chemical mechanism, but act on different substrates. What does this best illustrate?

A protein family built on homologous domains and a shared catalytic

mechanism, with other regions differing enough to change substrate

specificity

Which pairing of a protein to its functional class is correct?

Rhodopsin — receptor protein; ferritin — storage protein

A missense mutation replaces a valine buried in a protein's core with glutamate. What is the most likely consequence?

Destabilization of the folded state, because a charged side chain is forced

into the hydrophobic core — the protein may misfold and be targeted for

degradation

A purified protein is denatured in concentrated urea and refolds into its original

conformation when the urea is removed. What does this experiment establish?

All of the information needed to specify a protein’s three-dimensional

shape is contained in its amino acid sequence

Which statement correctly assigns covalent versus noncovalent character to the interactions that build a protein?

Peptide bonds and disulfide bonds are covalent, while hydrogen bonds,

van der Waals attractions, and electrostatic attractions are noncovalent

One enzyme is switched OFF when CTP binds a regulatory site; a different

enzyme is switched ON when ADP binds a separate site. Which statement about allosteric regulation is correct?

Both are allosteric regulation — one negative, one positive

In the bacterial aspartate pathway, lysine inhibits an early shared enzyme while

threonine, methionine, and isoleucine each independently inhibit enzymes in their own branches. Why is this arrangement useful?

It lets each branch shut down independently when its own end product

accumulates, without shutting off production of the others

Which statement about regulation by phosphorylation is correct?

A protein kinase transfers a phosphate from ATP onto a side chain such

as serine, and depending on the protein this may switch it ON or OFF; a

protein phosphatase reverses it

The p53 protein carries phosphate groups, acetyl groups, and ubiquitin at many different positions along its length, in different combinations. What does this pattern best demonstrate?

Different combinations of covalent modifications can control where a

protein is located, what it does, and when it is destroyed

A mutant Ras-like G protein can still bind GTP but cannot hydrolyze it. What

is the predicted outcome, and which regulator is rendered ineffective?

The protein is locked ON, and GAPs are ineffective because they work

by stimulating GTP hydrolysis

Which of the following are correct?

Both are correct

Two different human proteins are each found to contain one copy of the same

structural domain. Which conclusion is best supported?

Most proteins contain multiple domains, and the same domain can

appear in different proteins — domains act as reusable structural and

functional modules

Which statement about chromatin domains is correct?

Constitutive heterochromatin is always heterochromatic, while

facultative heterochromatin varies by chromosome, cell type, and

developmental state

The nucleolus is the site where:

rRNA genes are transcribed into rRNA

Which pairing of an H3 tail modification with its functional outcome is correct?

Trimethyl K9 → heterochromatin formation and gene silencing;

trimethyl K4 plus acetyl K9 → gene expression

A UV-induced thymine dimer forms when:

A cyclobutane ring forms between adjacent thymine, which can then no

longer pair with adenines

Most DNA repair involves which three general steps, in order?

Excision -> re-synthesis -> ligation

**In non-homologous end joining, the broken ends are:

Trimmed flush by specialized nucleases and joined by a specialized

DNA ligase, with loss of some nucleotides

**Homologous recombination repairs double-strand breaks:

After DNA replication but before sister chromatids separate, using the

undamaged sister chromatid as a template, with no loss of nucleotides

**Which statement about the mismatch repair system is correct?

It corrects errors that escaped proofreading by excising the incorrect

base from the newly synthesized strand and resynthesizing from the

original parent strand

What supplies the energy for forming each new phosphodiester bond during

DNA synthesis?

The incoming nucleoside triphosphate itself — the release of

pyrophosphate drives the addition onto the growing chain

A DNA polymerase variant retains full 5′ to 3′ polymerase activity but has lost

its 3′ to 5′ exonuclease activity. What is the predicted consequence?

Synthesis continues, but with a substantially higher error rate, because

a misincorporated nucleotide can no longer be removed and replaced

The mismatch repair system must determine which strand carries the error. Why is this essential?

Excising the base from the parent strand instead would convert a

temporary replication error into a permanent mutation

Cytosine in a DNA duplex undergoes deamination and is not repaired before the next round of replication. What is the outcome?

Uracil pairs with adenine, so one daughter duplex carries a permanent

change in which the original G is replaced by an A, while the other duplex

retains the original sequence

An adenine is lost by depurination, and the lesion is not repaired before

replication. What is the most likely result?

The site has no base to template, and an A–T nucleotide pair is deleted

in one of the two daughter duplexes

Why is ultraviolet light effective for decontaminating surfaces and equipment?

It induces cyclobutane rings between adjacent thymines; the joined

thymines can no longer pair with adenines, which blocks normal use of the

DNA

A double-strand break occurs in G1, before the chromosome has been

replicated. Which repair pathway will the cell use, and at what cost?

Non-homologous end joining, because no sister chromatid is available as

a template — at the cost of losing some nucleotides at the repair site

Place the steps of homologous recombination in the correct order: (1) strand

invasion of the undamaged duplex, (2) nuclease digestion of 5′ ends, (3) repair

synthesis, (4) ligation.

2 -> 1 -> 3 -> 4

Which statements comparing non-homologous end joining with homologous

recombination are correct?

All of the above

A patient's cells cannot excise damaged or mismatched bases and show

extreme sensitivity to sunlight. Which general repair strategy is compromised?

Excision-based repair — excision of the damaged segment, re-synthesis

by repair polymerase, then ligation; lecture links this failure to xeroderma

pigmentosum

In sickle-cell disease, a single nucleotide change in the β-globin gene replaces

glutamic acid with valine. Which conclusion is best supported?

A single nucleotide substitution changes one codon and therefore one

amino acid, and that one change can alter the protein enough to deform the

entire cell

The incidence of colon cancer is near zero until roughly age 40 and then climbs

steeply. What best explains this, based on DNA repair?

DNA damage occurs continually and repair is very good but not perfect,

so unrepaired mutations accumulate over a lifetime and the chance that a

cell has acquired a damaging combination rises sharply with age

Which of the following are true of a mutation that escapes repair before the

next round of replication?

Both are correct