Cell and Molec Final

Most proteins destined to enter the endoplasmic reticulum:

Begin to cross the membrane while still being synthesized

What is false about the leading edge of a lamellipodium?

Capping proteins bind to the minus end of actin filaments

What is *false* about tumor suppressor genes?

Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells -They will behave normally

What statement about vesicle budding from the Golgi is false?

Clathrin molecules are important for binding to and selecting cargos for transport.

What is *not* a common feature of beta sheets?

Coiled-coil patterns

Operons:

Contain a cluster of genes transcribed by a single mRNA

New membrane phospholipids are synthesized by enzymes bound to the ______ side of the _______ membrane

Cytosolic ; endoplasmic reticulum

The repair of mismatched base pairs of damaged nucleotides in a DNA strand requires a multistep process. What is the sequence of events of this process?

DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase

What mechanism is not directly involved in inactivating an activated RTK?

Dephosphorylation by serine/threonine phosphatases

Why does MyoD cause fibroblasts to express muscle-specific genes?

During they developmental history, fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells

If cells form coated pits but vesicle budding and the removal of coat proteins don't happen, what proteins are lacking?

Dynamin

DNA replication is considered semi-conservative because:

Each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand

What is true about DNA and replication?

Each strand of DNA contains all the information needed to create a new double-stranded DNA molecule with the same sequence information

What statement about exons 2 and 3 are the most accurate?

Exons 2 and 3 must contain a number of nucleotides that when divided by 3, leaves the same remainder (0,1, or 2)

T/F: ATPases generate ATP for the cell

False. ATPase hydrolyze ATP; they do not produce it.

T/F: Action potentials are usually mediated by voltage-gated Ca2+ channels

False. Action potentials are mediated by voltage-gated Na+ channels

T/F: A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic alpha helix

False. An embedded protein employs an amphipathic helix. The hydrophobic side interacts with the fatty acid tails of the membrane lipids and the hydrophilic portion interacts with the aqueous components of the cytosol

T/F: Feedback inhibition is defined as a mechanism of down-regulating enzyme activity by the accumulation of a product earlier in the pathway

False. Feedback inhibition occurs when an enzyme acting early in a pathway is inhibited by the accumulation of a product late in the pathway

T/F: STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription

False. JAK proteins are receptor-associated kinases that phosphorylate the transcriptional regulators called STAT proteins

T/F: Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer

False. Lipid-linked proteins are classified as integral membrane proteins b/c although they are not transmembrane proteins, they are covalently bound to membrane lipids and cannot be dissociated without disrupting the membrane's integrity

T/F: MAP kinase is important for phosphorylating MAP kinase kinase

False. MAP kinase kinase phosphorylates MAP kinase

T/F: Protein phosphorylation is another way to alter the conformation of an enzyme and serves exclusively as a mechanism to increase enzyme activity

False. Phosphorylation of a protein can change its conformation, this act can either increase or decrease the activity of the enzyme.

T/F: Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP

False. Ras exchanges its GDP for GTP when activated by an RTK

T/F: The amino acids in the interior of a protein do not interact with the ligand and do not play a role in specific binding

False. The interior amino acids are important for the structure that directly interacts with the ligand. Changes to these aa can change the protein shape and make it nonfunctional

T/F: Antibodies are Y shaped and are composed of six different polypeptide chains

False. They are Y shaped, but they are composed of 4 polypeptide chains: 2 heavy and 2 light

T/F: Membrane proteins that pump ions in and out of the cell are classified as enzymes

False. They are classified as transporters

T/F: Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential

False. Voltage-gated K+ channels respond more slowly than voltage-gated Na+ channels. They do not open until the action potential reaches its peak, and therefore do not affect its magnitude

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?

Flippases

A double-stranded DNA molecule can be separated into single strands by heating it up to 90 Celsius because:

Heat disrupts hydrogen bonding between complementary nucleotides

The dark speckled regions are locations of particularly compact chromosomal segments called

Heterochromatin

What DNA sequence is *not* commonly carried on mobile genetic elements?

Holiday junction

Although all protein structures are unique, there are some structural building blocks that are referred to as secondary structures. Some have alpha helices, some have B sheets, and others have a combo of both. What makes it possible for proteins to have these common structural elements?

Hydrogen bonds along the protein backbone

The endogenous GTPase activity of G-proteins serves to:

Hydrolyze GTP returning the G protein to its inactive, pre-stimulated level of activity

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. What best describes the population of channels exposed to such a threshold?

Some channels remain closed and some open completely

What is true about differentiated cells?

Some of the proteins found in differentiated cells are found in all cells of a multicellular organism

The microtubules in a cell form a structural framework that does everything but:

Strengthening the plasma membrane. -That is the job of an actin filament

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. What type of gating mechanism do these cells use?

Stress-gated

What is false about polypeptide chains?

The "polypeptide backbone" refers to all atoms in a polypeptide chain, except for those that form the peptide bonds

The Figure below shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, what must be TRUE?

The C-terminus of this protein is cytoplasmic

What happens when a cell-surface receptor activates a G protein?

The alpha subunit exchanges its bound GDP for GTP

What is *false* about actin?

The dynamic instability of actin filaments is important for cell movement -Dynamic instability is a phenomenon associated with microtubules, not actin

What condition would lead to signal-independent modification of the membrane lipids by Rafty?

The expression of a constitutively active phospholipase C

DNA Polymerase catalyzes the joining of a nucleotide to the growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?

The hydrolysis of PPi to Pi + Pi

What is *true* about secretion?

The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior

Hyperpolarized Membrane

The plasma membrane voltage becomes more negative relative to its resting membrane potential

Depolarized Membrane

The plasma membrane voltage becomes more positive relative to its resting membrane potential

What is true about DNA?

The polarity of a DNA strand results from the polarity of the nucleotide subunits

If you remove the ER-retention signal from a soluble protein that normally resides in the ER lumen, where do you predict the protein will ultimately end up?

The protein would end up in the extracellular space. Normally the protein would go from ER to Golgi, then return to the ER b/c of its signal. Without the signal, the protein would leave the Golgi via the default pathway and become secreted into the extracellular space

What is the main reason that a typical eukaryotic gene is able to respond to a far greater variety of regulatory signals than a typical prokaryotic gene or operon?

The transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter

T/F: A protein that relies on protein-protein interactions to stabilize its membrane association is classified as a peripheral membrane protein because it can be dissociated without the use of detergents

True

T/F: GTP binding proteins typically have GTPase activity and the hydrolysis of GTP transforms them to the off conformation

True

T/F: If an enzyme's allosteric binding site is occupied, the enzyme may adopt an alternative conformation that is not optimal for catalysis

True

T/F: Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane

True

T/F: PI 3-kinase phosphorylates a phospholipid in the plasma membrane

True

T/F: Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon

True

The process of sorting human chromosomes pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes painted?

Using fluorescent DNA molecules

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by:

Using the energy of ATP hydrolysis to move nucleosomes

Mouse embryonic stem cells (ES):

come from the inner cell mass of early embryos

Hemidesmosomes are important for:

Attaching epithelial cells to the extracellular matrix

Resting Membrane Potential

Membrane potential at a steady rate at which the flow of positive and negative ions across the plasma membrane is balanced, so no further charge differences accumulate across the membrane

Cholesterol serves several essential functions in mammalian cells. What is *not* influenced by cholesterol?

Membrane thickness

Which amino acid would you expect a tRNA with the anticodon 5'-CUU-3' to carry?

-Anticodon is given from 5'-3' -Complement: 5'-AAG-3' -Lysine

Which amino acid will be on the tRNA that is the first to bind to the A-site of the ribosome?

-Third codon of the protein

List 3 ways the lateral mobility of plasma membrane proteins can be restricted

1) attached/anchored to intracellular cytoskeletal elements 2) attached/anchored to extracellular matrix 3) attached to receptors on other cells 4) tight junction b/w cells prevents diffusion between apical and basal part of cells

Homologous recombination is an important mechanism in which organisms use a "back-up" copy of the DNA as a template to fix double-strand breaks without loss of genetic information. What is *not* necessary for homologous recombination to occur?

5' DNA strand overhangs

What situation would lead to relaxation of smooth muscle cells in the absence of acetylcholine?

A muscle cell that has a defect in guanylyl cyclase such that it constitutively converts a GTP to cGMP

What genetic change *cannot* convert a proto-oncogene into an oncogene?

A mutation that introduces a stop codon immediately after the codon for the initiator methionine

What is *false* about the unfolded protein response (UPR)?

Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins -The receptors for the unfolded proteins are on the ER membrane, and the sense the misfolded proteins using their luminal domains

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called:

Active transport

Thymosin is a protein that can bind actin monomers. If you added a drug that inhibits the ability of thymosin to bind actin, how would this affect actin polymerization?

Addition of a drug that keeps thymosin from binding actin will increase the rate of actin polymerization in the cell

Induced pluripotent stem cells:

Are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types

Tight junctions:

Are formed from claudins and occludins

What is false about Bad and Bcl2?

In the absence of survival signal, Bad is phosphorylated

New membrane synthesis occurs by:

Incorporation of phospholipids into one face of a preexisting membrane and their specific redistribution by flippases

What is *false* about integrins?

Integrins use adaptor proteins to interact with the microtubule cytoskeleton

A basal lamina:

Is a thin layer of extracellular matrix underlying an epithelium

The core histones are small, basic proteins that have a globular domain at the C-terminus and a long extended conformation at the N-terminus. What is *not* true of the N-terminal tail of these histones?

It binds to DNA in a sequence-specific manner

What is the role of the nuclear localization sequence in a nuclear protein?

It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore

What is true about the newly synthesized strand of a human chromosome?

It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis

What is *false* about molecular switches?

Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off

Ca2+ pumps in the plasma membrane and ER are important for:

Preventing Ca2+ from altering the activity of molecules in the ctyosol

The DNA from two different species can often be distinguished by a difference in the:

Ratio of A + T to G + C

The sigma subunit of bacterial RNA Polymerase:

Recognizes the promoter sites in the DNA

What is *false* about riboswitches?

Riboswitches are made from rRNAs

What shortens during muscle contraction?

Sarcomeres