3-4 Biochem Flashcards by Lovely Marie Villar

Why is Protein considered Life?

On a biochemical and molecular standpoint, the processes that define life are rooted in cellular activity wherein the work is done by proteins

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The Structural Foundation of Proteins refers to the architecture of ___ and ___

Cells and Tissues

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Which proteins provide a functional role?

Enzymes, Receptors, Carrier Proteins (Hormones and Neurotransmitters)

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What is the function of enzymes?

Catalyze the vast majority of cellular processes and reaction, whether for growth or survival

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Proteins also mediate signaling, helping cells communicate with each other, such as hormones and neurotransmitters. True or False?

TRUE

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Amino acids are the building blocks of proteins. True or False?

TRUE

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What bond joins amino acids together? Is it a Covalent Bond?

Peptide Bonds, Yes

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Amino acids are composed of?

Amino Group (-NH2 ) (-NH3 + if not attached)
Side Chain (Functional Group)
Carboxyl Group (-COOH)

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Glycine is the tiniest Amino Acid and has a side chain?

False, Glycine does not have a side chain

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At physiologic pH (∼7.4), an amino acid typically exists in a zwitterionic form, where the molecule has both a ____ charge on the amino group and a ____ charge on the carboxyl group, thus is electrically neutral

Positive, Negative

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Why is the Side chain considered the functional group?

It’s what makes the amino acid “unique.” It is variable per amino acid and provides different functions

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Which parts of the amino acid interact to form a peptide bond?

Carboxyl Group of one amino acid and the Amino group of another Amino Acid

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How do we classify Amino Acids in terms of Structural and Chemical Properties?

Aliphatic - Linear Structure
Aromatic - Cyclic Structure (Bulky/Big Chains)

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Describe the Polarity of Amino Acids

Polar: Possess a side chain that is able to react to solutes in water (Hydroxyl, Sulfide, Amino Group, Carboxyl Group), found in outer surfaces of a protein
Non-Polar: Hydrophobic in nature and repel water, found in inner surfaces of a protein (away from the surrounding water)

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Proteolysis alters the “secondary” structure and subsequently alters the proteins’ higher order structures as well.

False, the primary structure is altered

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Differentiate Hydrophilic vs Hydrophobic Amino Acids

Hydrophilic: Dissolves well in water
Hydrophobic: Insoluble in Water and is Less Soluble in Blood but mixes well with lipids

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At physiologic pH, Polar Amino Acids can have a positive (basic) or negative charge (acidic). True or False?

TRUE

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What are the practical or operational groupings of Amino Acids

Small and Compact
Sulfur Containing
Branched-chain amino acids
Large, Aromatic

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Provide specific examples of Amino Acids under each practical and operational grouping

Small and Compact (Glycine and Proline)
Sulfur Containing (Cysteine and Methionine)
Branched-chain amino acids (Valine, Leucine, Isoleucine)
Large, Aromatic (Tryptophan, Tyrosine, and Histidine)

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Describe the characteristics of Glycine and Proline as small and compact amino acids

Forms Folds, Bends, Kinks in the structure of Polypeptide

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What are the functions of branched-chain amino acids (BCAAs - Valine, Leucine, Isoleucine)

Play a vital role in neuronal metabolism, major amino acid food for the brain
All 3 act as energy reserves for the brain
Forms a big chunk of lean muscle mass. This is why there are BCAA supplements available for gaining muscle mass.

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Where do hydrophobic amino acids tend to be found?

In the interior of typical plasma protein

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When protein travels with the blood along the body, what elements are the protein exposed to?

Other cells, different molecules, compounds, acids and other proteins

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Differentiate the interior and exterior of amino acids

Interior: Compact; hydrophobic amino acids (help stabilize structure) are here such as Gly, Phe, Val, Leu
Exterior: More exposed to surrounding environment; polar amino acids are here such as Glu, Asp, Tyr, Ser; have reactive side chains

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Which amino acid has an oily or lipid like property and what does it promote?

Non-polar amino acid, promotes hydrophobic interactions

What phenomenon refers to the side chains of nonpolar amino acids clustering together in the interior of the protein?

Hydrophobic effect, which is the result of the hydrophobicity of the non polar R groups

Which part of the protein are the nonpolar R groups found?

Surface of the protein interacting with the lipid environment

What disease cause red blood cells to become sickle shaped rather than disc shaped?

Sickle cell anemia

Sickle cell anemia results from what?

from the replacement of polar glutamate with nonpolar valine at the sixth position in the β subunit of hemoglobin A.

What is the most common mutation associated with cystic fibrosis and what does it result into?

3-bp deletion which results into the loss of phenylalanine at position 508, weakening hydrophobic interactions leading to misfolding.

What protein component of LDL and HDL is responsible for interacting with tissue receptors?

Apoprotein, which possess polar amino acids in its interactive sites

Main difference between non-essential from essential amino acids:

Essential: Must be taken up through one’s diet because the body doesn’t have the enzymatic machinery to produce these amino acids Non-essential: Made within the body

Examples of Non-essential amino acids

Glycine, proline

Essential Amino Acids Mnemonic

PVT - Phenylalanine, valine, threonine TIM - Tryptophan, isoleucine, methionine HALL - Histidine, arginine, leucine, lysine

Example of a conditionally essential amino acid

Arginine

What amino acids can be converted into both glucose and ketone bodies (glucogenic and ketogenic)?

IPTTT - isoleucine, phenylalanine, tyrosine, tryptophan, threonine

What amino acids can only be converted into ketone bodies (exclusively ketogenic)?

LL - leucine, lysine

What are the building blocks of peptides; joined by the peptide bonds?

Amino acids

What structure is the basic linear sequence of amino acids?

Primary

What structure is composed of the alpha helices, beta-plated sheets?

Secondary

What structure is composed of folds and domains, makes up a 3D conformation?

Tertiary

What are long sequence of amino acids joined together, interchangeable with the term protein?

Polypeptide

The sequence of amino acids in a polypeptide has directionality which starts from ______ and ends at _________?

N-terminus (amino terminus) and C-terminus (carboxyl terminus)

Tertiary structure is not just a helix or a sheet, they can fold over each other. True or False?

TRUE

What structure is applicable to proteins with multiple subunits/chains/polypeptide?

Quaternary structure

What connects each amino acid?

Peptide bond

In the secondary structure, the beta pleated sheets have linear arrangement of amino acids that are antiparallel to each other. True or False?

TRUE

Most of the plasma proteins dissolved in blood assumes what shape?

Tertiary structure

______ look like they are twisted into a coil when imagined in a 3D conformation

Alpha-helices / alpha helix

Arrangement wherein each of the amino acid side chains are arranged side by side.

Beta-pleated sheets

Which bonds stabilize the primary structure of amino acids?

Peptide bonds

Which bonds stabilize the secondary structure of amino acids?

Hydrogen bonds

________ are an expanded form of the alpha-helices where there is more complex arrangements of the alpha-helices and beta-pleated sheets

Supersecondary Structures

What are the different alpha helix motifs?

Helix-turn-helix (HTH) Helix-loop=helix (HLH) Coiled-coil

What causes the Helix-turn-helix (HTH) to have a turn/kink/bend?

The presence of proline residue

Explain why proline causes a kink/bend in the polypeptide structure.

Proline’s side chain continues onto the amino group

Differentiate Greek key from β-barrel.

Greek key: formed when a polypeptide chain doubles back on itself β-barrel: formed when β-sheets are extensive enough to fold back on itself

In a β-α-β motif, two linear strands of β-sheets are connected by a stretch of an alpha-helix. True or False?

FALSE

Important structure that interacts with DNA and makes transcription an optimal process

Zinc finger

What is the difference of a hydrogen bond in the tertiary structure than that of in the secondary structure?

The hydrogen bonds form between the side chains instead of between the amino groups

Ionic bonds occur between two amino acids with identical charges. True or False?

FALSE

Give an example of an acidic amino acid.

Aspartate Glutamate

Give an example of a basic amino acid

Histidine Lysine Arginine

Ionic bonds are also called _______ because of the similarity in how this is made.

Salt bridge

Disulfide bonds are formed between two _____ groups.

Sulfhydryl

A special type of interaction that is applicable for nonpolar amino acids.

Hydrophobic Interaction

The Van der Waals forces are the weakest forces or interactions but they also contribute to the stability of the proteins. True or False?

TRUE

What are the two (2) prototypical structures formed from the interaction of different amino acids?

Fibrous Proteins Globular Proteins (globins)

This structure is present in proteins made up of 2 or more polypeptide chains.

Quaternary Structure

How many linear proteins or peptide chains is collagen composed of?

Collagen is an example of a _____ protein

Fibrous

Enumerate and differentiate the two (2) important components of collagen.

Glycine - smallest amino acid, creates folds to allow triple helix structure Lysine - relatively long, forms cross-links which strengthen the 3 chains of collagen

Hemoglobin is an example of a ______ protein

Globular / globin

What are the four (4) globular subunits of hemoglobin?

2 β-chains and 2 α-chains

What happens to a protein when its primary structure is altered?

the protein becomes dysfunctional

What is an example of a primary structure alteration due to a point mutation?

Sickle Cell Anemia, where glutamate is replaced by valine

How does deletion or insertion mutations affect protein structure?

They create shorter or longer proteins.

What is a silent mutation, and how does it affect the protein?*

A silent mutation changes the primary structure but does not significantly affect the protein’s function.

What are the main components of a protein's secondary structure?

Alpha helices and beta-pleated sheets.

What is a prion disease, and how does it affect protein structure?

Prion diseases are protein conformation diseases where normal alpha-helices are replaced by abnormal beta-pleated sheets, leading to aggregate formation in neurons.

How does altering the tertiary structure of a protein affect its function?

It can lead to misfolding of the protein, disrupting its function or structural integrity.

Differentiate between denaturation and misfolding of proteins at the tertiary level.

Denaturation results from the destruction of peptide bonds at the primary level, while misfolding involves disruption of interactions at the tertiary level without breaking peptide bonds.

What are the potential consequences of protein misfolding in neurons?

Accumulation of misfolded proteins can lead to cell injury, cell death, and neurological decline.

What is the consequence of disrupting the quaternary structure of a protein?

It can lead to a loss of function of that protein.

Which condition results from a dietary deficiency of vitamin C affecting collagen synthesis?

Scurvy, which undermines the conformational stability of collagen fibers

What makes proteins crucial for acid-base balance?

Structure: carboxyl groups (COOH/COO-) and amino groups (NH3+/NH2)

List the acidic and basic amino acids

Acidic: Aspartate & Glutamate | Basic: Histidine, Arginine, & Glutamate

Differentiate protonation and deprotonation

Protonation - donate or release protons ; Deprotonation - bind or accept protons

T or F. Acidic environment has no hydrogen ions.

F. "As the environment gets more alkaline = less and less H+ ions."

What kind of environment/medium does deprotonation mostly occur?

relatively Alkaline environments/mediums

Primary buffer of blood pH

Histidine

At pH 7, the side chains of _____ are _% protonated and _% not protonated.

Histidine, 9, 91

Needed pKa of the primary buffer of blood pH to stay in its middle state

Plasma protein that can also buffer blood pH

Albumin

Characteristics of albumin that makes it suitable as blood pH buffer

High molecular weight = abundant amino acid residues participating in the protonation and deprotonation processes

What role do compounds containing O or N play in proteins?

Serve as hydrogen bond donors and/or acceptors

How does a change in pH affect proteins?

Alter hydrogen bonding, leading to structural and functional changes

The process of _______ and ________ alter hydrogen ions present in the functional groups of amino acids.

Protonation, deprotonation

Which functional groups in amino acids are affected by changes in pH through protonation and deprotonation?

Carboxylic group and amino group

What happens when proteins release or bind H ions?

Disruption of hydrogen bonds, forming new bonds and disrupting old ones

The disruption of hydrogen bonds in proteins can lead to a loss of __________.

Function

In the context of pH changes, proteins that are not designed to buffer may lead to __________ in tissues.

Dysfunction

What are the two types of protein structures affected by pH changes?

Secondary and tertiary structures

Disruption of hydrogen bonds in response to _____ can lead to protein structural changes.

Acidosis/Alkalosis

In critically ill patients, progressive protein dysfunction can lead to __________.

Multiple organ failure.

Patients who suffer from heart attack or severe blood loss, have tissues generating plenty of _______ due to lack of oxygen to be used.

Lactic acid

What changes occur in heart proteins during acidosis?

Proteins become protonated, disrupting their structure

What are the functional consequences of protein disruption in the heart due to acidosis?

Loss of contractility, impaired enzyme function, and misfolded receptors lead to compromised cell-to-cell communication

How does acidosis contribute to the weakening of the heart?

Disrupted protein function results in decreased contractility and overall heart function

Changes in pH can cause proteins in white blood cells to become __________, impairing immune response.

Sub-optimal

Besides pH, what other factors can alter the molecular structure of biological systems?

Temperature and other environmental parameters

What is the outcome of significant pH changes?

Loss of homeostasis, leading to multiple organ failure and potential death

What complications are seen during multiple organ failure?

Septic shock, severe shock, trauma, infections, stage 4 cancer, major surgery, and significant blood loss

What is the cumulative effect of the small changes caused by the fluctuation of a patient’s blood?

"Dying from a thousand cuts," eventual death

Provide the three amino acids that are highly active in metabolism.

(ADE) Alanine, Aspartate, Glutamate

What is the prototypical glucogenic amino acid?

(A) Alanine

Amino acid that forms part of the building blocks of purine and pyrimidine molecules, as well as a precursor of heme.

(G) Glycine

Amino acid that is coded by the start codon AUG in eukaryotic translation.

(M) Methionine

What are the three branched-chain amino acids (BCAA)?

(VIL) Valine, Isoleucine, Leucine

What is the active component of glutathione?

Provide the three amino acids that contain a hydroxyl (-OH) group.

(STY) Serine, Threonine, Tyrosine

_____ are signaling molecules that cells use to communicate with other cells.

Cytokines

What makes mucus sticky and thick?

Disulfide Bonds

What is given in paracetamol-induced liver injury to neutralize free radicals?

N-acetylscysteine (NAC)

What is the most abundant protein in the body made up of?

Cross-linked fibers

Give the 4 semi recurring units collagen is composed of.

Proline, Glycine, Hydroxyproline and Hydroxylysine

True or False: Both vitamin C and copper are needed to have very strong collagen.

TRUE

What is the smallest hormone that is a direct derivative of tyrosine?

Thyroid hormone

Tyrosine derivatives that are used as the main signaling molecule by the Sympathetic Nervous System.

Cathecolamines

Where is the vast majority of serotonin found?

Intestines or gut

_______ is the precursor of melatonin, which makes it a tryptophan derivative.

Serotonin

Most notable function of melatonin.

Sleep

Acts as the precursor of GABA (most abundant inhibitory neurotransmitter).

Glutamate

What does GABA stand for?

Gamma-aminobutyricacid

What makes histamine a versatile molecule?

Neurotransmitter in the brain, Mediator of inflammation, and Vital vasoactive substance

Derivative of Glycine as an amino acid precursor.

Glycine

What is the 21st amino acid that is formed when the oxygen of Serine is replaced by Selenium?

Selenocysteine (Sec)

What amino acid is Selenocysteine derived from?

Serine (Ser)

What are proteins or enzymes that contain Selenium?

Selenoproteins

Give the 2 important selenoproteins.

Thyroid deiodinase and Glutathione peroxidase

Which selenoprotein converts thyroxine to triiodothyronine leading to the removal of 1 iodine atom, and is essential in optimal thyroid function?

Thyroid deiodinase

Which selenoprotein ensures that the function of glutathoine is well-regulated?

Glutathione peroxidase

What disease is characterized by cardiac failure due to accumulated oxidative injury?

Keshan disease

What are the 2 amino acids related to Arginine and involved in ammonia detoxification?

Ornithine and Citrulline

What is the amino acid known as the precursor for heme, found in hemoglobin, and derived from Glycine?

δ-Aminolevulinic acid

What amino acid is neuroprotective, an antioxidant, and considered essential in infants?

Taurine

What amino acid is the key component of hair, skin, connective tissues, and digestive enzymes as a unit of mechanical linkage?

Cystine

What are the three complex or conjugated protein-based molecules and their descriptions?

Glycoproteins: proteins linked with sugar Proteoglycans: proteins linked with larger sugars Lipoproteins: a lipid structure with a protein attached to it

What are the three main types of glycoprotein linkages?

N-linked (attached to asparagine via N-acetylglucosamine) O-linked (attached to the -OH groups of serine, threonine, and hydroxyproline via N-acetylgalactosamine) GPI linkage/anchor (glycosylphosphatidylinositol)

What are the key roles of glycoproteins?

cell-to-cell identification, recognition, and signaling intracellular trafficking regulation of viscosity and lubrication in secretions (mucins) transport of molecules like transferrin and ceruloplasmin components of several hormones such as FSH, LH, TSH, and hCG mediate platelet function binding of viruses and parasites

Malaria (Plasmodium vivax) binds to RBC receptors known as:

Duffy blood group antigen

These bind to neurons via N-CAMs (neural cell adhesion molecules) and guarantee death if intervention is not given in a timely manner.

Rabies viruses

They are bigger molecules that still have a core protein with many projections (i.e., glycosaminoglycans), each of which is a combination of amino groups and carbohydrates/saccharide groups. They are abundant in connective tissue, particularly in the extracellular matrix (ECM).

Proteoglycans

What are the key functions of proteoglycans?

strengthen connective tissue enhance joint flexibility improve the texture and consistency of cartilage

They are linear polysaccharides that have repeating blocks of amino sugars (N-acetylglucosamine, N-acetylgalactosamine) bound to uronic acids (glucuronic acid, iduronic acid).

Glycosaminoglycans (GAGs)

It functions as the backbone of many glycosaminoglycans (GAGs), consists of an unbranched chain of repeating disaccharide units, and plays an important role in permitting cell migration during morphogenesis and wound repair.

Hyaluronic acid (non-sulfated)

It is often given as a supplement for individuals with joint diseases.

Hyaluronan

It is found in cartilage, the cornea, and intervertebral discs, plays a role in maintaining the structure and function of tissues, and exists in two main forms: KSI (found in the cornea) and KSII (found in cartilage and intervertebral discs).

Keratan sulfate

It is present in proteoglycans found on many extracellular surfaces, is associated with the plasma membrane of cells, functions as a receptor, and plays a critical role in mediating cell growth and cell-cell communication.

Heparan sulfate

It plays a crucial role in maintaining the structure of the extracellular matrix (ECM), is located at sites of calcification in endochondral bone and cartilage, and is also found in the ECM of the CNS, where it acts as a signaling molecule in preventing the repair of nerve endings after injury.

Chondroitin sulfate

It provides the sulfur molecules required for the sulfation of glycosaminoglycans.

Cysteine

What is the disorder associated with joint stiffness and respiratory failure due to inability of lysosomes to degrade GAGs?

Mucopolysaccharidoses

A multidomain core protein with more complex sugars, bound to GAGs

Proteoglycans

Proteoglycans combine with __ for supportive and protective functions in the ECM.

collagen

glycoprotein's oligosaccharide chains are ____ bonded.

covalently

Found on the cell membrane for recognition and interaction

glycoprotein

Are proteoglycans negatively or positively charged?

negative

Involved in blood groups ABO

glycoprotein

This is the main transport mechanism of lipids in the bloodstream.

lipoproteins

The lipid coat of lipoproteins can transport:

cholesterol, esthers, triglycerides

allows the lipoprotein to bind to receptors, enter organs

apoprotein

this is mobilized by lipoproteins in times of increased energy demand

triglycerides

The result when dietary lipids fails to reach the liver/adipose tissue that leads to premature activation of digestive enzymes

acute pancreatitis

Complication when cholesteral and fat are deposited in blood vessels, forming plaque

early onset atherosclerotic cardiovascular disease

other diseases associated with defects in lipoproteins

fatty liver, diabetes mellitus, metabolic syndrome

lipemic serum has a ____ appearance due to too much oil/fat consumption

milky

Which of the following is not a role of biological membranes? A. Like enzymes, it speeds up the transport of large molecular weight solutes along the semi- permeable membrane B. It participates in the proper maintenance of ionic charges within cells and their surroundings C. It prevents enzymes from acting in areas where they may cause cell lysis and degradation D. It defines boundaries inside the cell itself

A. Like enzymes, it speeds up the transport of large molecular weight solutes along the semi-permeable membrane

B. Magnesium

C. Liposome

A. As temperature increases, membrane fluidity increases

In general, what is the relationship of cholesterol with membrane fluidity? A. Below melting temperature, membrane fluidity increases with an increase in cholesterol B. Above melting temperature, an increase in cholesterol limits fluidity C. Both A and B are correct D. Both A and B are incorrect

C. Both A and B are correct

Biological Membranes are said to be asymmetric because of the unequal distribution of phospholipids in the inner and outer leaflet of membranes. Which of the following phospholipids is most commonly seen in the inner leaflet of membranes? A. Phosphatidylethanolamine B. Phosphatidic acid C. Phosphatidylcholine D. Sphingomyelin

A. Phosphatidylethanolamine

Cellular degradation analysis shows a high preponderance of the enzyme ATP synthase. This most probably signifies: A. An extensive plasma membrane network in the cell B. A large amount of glucose-6-phosphatases C. A cell with plenty of mitochondria D. A very active Golgi Complex

C. A cell with plenty of mitochondria

In the sodium-potassium ATPase pump, phosphorylation of the Aspartic acid residue of the alpha subunit protein results in: A. The attachment of sodium ions to the alpha subunit B. An increase in the affinity of potassium ions to the alpha subunit C. The cleavage of aspartic acid from the Na-K-ATPase transport protein

B. An increase in the affinity of potassium ions to the alpha subunit

The drug digoxin, a digitalis derivative, inhibits the sodium-potassium-ATPase pump in myocardial cells. This results in: A. An increased synthesis of ATP in the cell B. An increase in the intracellular calcium ion concentration C. Depolarization of the cardiac cell D. Vasodilation

B. An increase in the intracellular calcium ion concentration

Which of the following is not a membrane lipid? A. Cholesterol B. Triacylglycerol C. Phosphatidylcholine D. Sphingomyelin

B. Triacylglycerol

Which of the following neurotransmitters activate muscle fibers in the neuromuscular junction? A. Acetylcholine B. Nicotine C. Dopamine D. Serotonin

A. Acetylcholine

Which of the following has the highest membrane permeability coefficient? A. Water B. Sodium C. Glucose D. Cortisol

B. Cortisol

Which of the following is equally distributed (same concentration) between the inner and outer leaflet of the lipid bilayer? A. Phosphatidylcholine B. Phosphatidylethanolamine C. Sphingomyelin D. None of the above

D. None of the above

Why is it more common to see lateral flip flops in cell membranes compared to transverse flip flops? A. Lateral flip flops happen more spontaneously compared to transverse flip flops B. Transverse flip flops tend to cause cell death C. Transverse flip flops are energy-requiring changes D. Lateral flip flops have to happen multiple times first before a transverse flip flop occurs

B. Transverse flip flops tend to cause cell death

All of the following are amphipathic molecules, EXCEPT: A. Peripheral membrane proteins B. Integral membrane proteins C. Free cholesterol D. Glycosphingolipids

A. Peripheral membrane proteins

Which of the following is a characteristic of a ligand-gated ion channel? A. It functions by hydrolyzing ATP to transport ions against their gradient. B. It remains permanently open once activated by a ligand. C. It opens or closes in response to the binding of a specific molecule. D. It allows the passage of nonpolar molecules across the membrane.

C. It opens or closes in response to the binding of a specific molecule.

What is the primary function of G-protein-coupled receptors (GPCRs)? A. Directly phosphorylating target proteins in the cell. B. Serving as ion channels for specific cations and anions. C. Transmitting signals from extracellular ligands to intracellular G-proteins. D. Degrading ligands after signal transduction.

C. Transmitting signals from extracellular ligands to intracellular G-proteins.

Which of the following does not participate in the signal transduction mechanism of receptor tyrosine kinases (RTKs)? A. Autophosphorylation of the receptor. B. Activation of downstream intracellular signaling proteins. C. Direct binding to and activation of nuclear DNA. D. Dimerization of the receptor upon ligand binding.

C. Direct binding to and activation of nuclear DNA.

In facilitated diffusion, which of the following is true? A. Molecules move against their concentration gradient with the help of carrier proteins. B. Energy in the form of ATP is required for the transport process. C. The transport process is saturable, meaning it can reach a maximum rate. D. It involves the direct interaction of small nonpolar molecules with the lipid bilayer.

C. The transport process is saturable, meaning it can reach a maximum rate.

Which of the following best describes the sodium-potassium pump (Na+/K+ ATPase)? A. It transports three sodium ions into the cell and two potassium ions out of the cell. B. It is a passive transport mechanism that does not require energy. C. It plays a critical role in maintaining the cell’s membrane potential. D. It allows for the passive diffusion of sodium and potassium ions across the membrane.

C. It plays a critical role in maintaining the cell’s membrane potential.

Which of the following statements about active transport is incorrect? A. Active transport can move molecules from areas of low concentration to high concentration. B. It requires energy, often in the form of ATP, to function. C. It is always coupled with the transport of another molecule in the same direction. D. It often involves carrier proteins that change shape during the transport process.

C. It is always coupled with the transport of another molecule in the same direction.

Which of the following types of transport does not require energy input? A. Active transport B. Facilitated diffusion C. Primary active transport D. Cotransport

B. Facilitated diffusion

What is the primary role of cholesterol in the plasma membrane? A. Increasing membrane permeability to ions B. Stabilizing membrane fluidity across temperature changes C. Acting as a receptor for extracellular signals D. Facilitating the transport of glucose into the cell

B. Stabilizing membrane fluidity across temperature changes

Which ion is most commonly pumped out of the cell by the Na+/K+ ATPase? A. Potassium B. Sodium C. Calcium D. Chloride

B. Sodium

Which of the following is not a characteristic of passive transport? A. Movement along a concentration gradient B. No energy expenditure C. Involvement of carrier proteins D. Requires ATP

D. Requires ATP

Which molecule can pass through the lipid bilayer without the need for a transport protein? A. Glucose B. Sodium ion C. Oxygen D. Protein

C. Oxygen

Which of the following best describes the fluid mosaic model of the plasma membrane? A. A rigid structure with fixed components B. A solid barrier impermeable to all molecules C. A dynamic structure with proteins and lipids that move laterally D. A double-layered membrane with immobile proteins

C. A dynamic structure with proteins and lipids that move laterally

What is the function of clathrin in vesicular transport? A. To hydrolyze ATP for vesicle movement B. To stabilize the plasma membrane C. To coat vesicles during endocytosis D. To act as a ligand for membrane receptors

C. To coat vesicles during endocytosis

In receptor-mediated endocytosis, which component binds to the ligand? A. Clathrin B. Adaptin C. Dynamin D. Receptor protein

D. Receptor protein

Which of the following is most directly responsible for the resting membrane potential of a cell? A. The Na+/K+ ATPase pump B. Ion channels in the membrane C. The concentration of glucose in the blood D. The synthesis of proteins

A. The Na+/K+ ATPase pump

What happens when a ligand binds to a G-protein-coupled receptor? A. The receptor becomes phosphorylated B. The receptor activates a G-protein C. The receptor directly opens an ion channel D. The receptor is endocytosed

B. The receptor activates a G-protein

Which of the following ions is typically found in higher concentration inside the cell compared to the outside? A. Sodium B. Potassium C. Chloride D. Calcium

B. Potassium

What is the role of aquaporins in the plasma membrane? A. Transporting ions B. Facilitating the diffusion of water C. Acting as receptors for hormones D. Transporting glucose

B. Facilitating the diffusion of water

Which component of the plasma membrane is primarily responsible for cell-cell recognition? A. Phospholipids B. Cholesterol C. Glycoproteins D. Integral proteins

C. Glycoproteins

Which of the following is true about ion channels? A. They require ATP to function. B. They are always open. C. They are selective for specific ions. D. They transport ions against their concentration gradient.

C. They are selective for specific ions.

Which of the following is not a characteristic of facilitated diffusion? A. It is a passive process. B. It involves carrier proteins. C. It can move substances against their concentration gradient. D. It does not require energy.

C. It can move substances against their concentration gradient.

Which of the following is true about the sodium-potassium pump? A. It pumps sodium into the cell and potassium out. B. It requires ATP to function. C. It is a type of facilitated diffusion. D. It only operates in nerve cells.

B. It requires ATP to function.

What is the function of the endoplasmic reticulum in membrane transport? A. Synthesizing proteins for secretion B. Synthesizing ATP for active transport C. Facilitating the passage of ions across the membrane D. Degrading misfolded proteins

A. Synthesizing proteins for secretion

Which of the following is a second messenger often involved in G-protein-coupled receptor signaling? A. cAMP B. ATP C. Na+ D. Glucose

A. cAMP

Which of the following statements is true regarding osmosis? A. Water moves from an area of low solute concentration to high solute concentration. B. Water moves from an area of high solute concentration to low solute concentration. C. Osmosis requires energy in the form of ATP. D. Osmosis involves the active transport of water molecules.

A. Water moves from an area of low solute concentration to high solute concentration.

What role does phosphatidylserine play in the plasma membrane? A. It is involved in cell signaling. B. It is responsible for cell-cell adhesion. C. It triggers apoptosis when found on the outer leaflet. D. It acts as a receptor for neurotransmitters.

C. It triggers apoptosis when found on the outer leaflet.

Which of the following is not involved in the transport of molecules across cell membranes? A. Ion channels B. Carrier proteins C. Ribosomes D. ATP-powered pumps

C. Ribosomes

Which type of molecule typically requires a transport protein to cross the cell membrane? A. Small nonpolar molecules B. Large polar molecules C. Gases like O2 and CO2 D. Lipid-soluble vitamins

B. Large polar molecules

What happens when an action potential reaches the axon terminal of a neuron? A. The membrane potential becomes negative. B. Voltage-gated calcium channels open. C. Sodium ions are released into the synaptic cleft. D. The neuron becomes hyperpolarized.

B. Voltage-gated calcium channels open.

Which of the following statements is true about membrane proteins? A. All membrane proteins are enzymes. B. They can function as receptors, channels, and transporters. C. They are always located on the outer surface of the membrane. D. They cannot move within the membrane.

B. They can function as receptors, channels, and transporters.

Which lipid is found in greater concentration in the outer leaflet of the plasma membrane? A. Phosphatidylinositol B. Phosphatidylethanolamine C. Phosphatidylcholine D. Cardiolipin

C. Phosphatidylcholine

Which process is used by cells to take in large molecules or particles? A. Exocytosis B. Endocytosis C. Diffusion D. Filtration

B. Endocytosis

Which of the following is not a role of phospholipids in the plasma membrane? A. Providing fluidity to the membrane B. Serving as receptors for signaling molecules C. Forming the basic structure of the membrane D. Contributing to membrane asymmetry

B. Serving as receptors for signaling molecules

Which of the following is true about receptor tyrosine kinases (RTKs)? A. They are involved in G-protein signaling. B. They dimerize and autophosphorylate upon ligand binding. C. They directly transport ions across the membrane. D. They are exclusively found in the nuclear membrane.

B. They dimerize and autophosphorylate upon ligand binding.

Which type of transport allows glucose to enter cells against its concentration gradient? A. Simple diffusion B. Facilitated diffusion C. Primary active transport D. Cotransport

D. Cotransport

Which of the following statements is true about the lipid bilayer? A. It is impermeable to all molecules. B. It allows free passage of large, charged molecules. C. It is composed primarily of phospholipids and proteins. D. It is symmetric in its lipid composition.

C. It is composed primarily of phospholipids and proteins.

Which of the following components is not part of the extracellular matrix? A. Collagen B. Elastin C. Phospholipids D. Proteoglycans

C. Phospholipids

Which type of receptor directly alters ion flow across the membrane when activated? A. G-protein-coupled receptor B. Ionotropic receptor C. Nuclear receptor D. Enzyme-linked receptor

B. Ionotropic receptor

Which of the following describes the role of ATP in active transport? A. ATP acts as a signal molecule. B. ATP is hydrolyzed to provide energy for transport. C. ATP binds to the transported molecules. D. ATP is not involved in active transport.

B. ATP is hydrolyzed to provide energy for transport.

Which type of cellular junction prevents the passage of molecules between cells in an epithelial layer? A. Tight junctions B. Gap junctions C. Desmosomes D. Adherens junctions

A. Tight junctions

What is the primary function of ion channels? A. Transporting large molecules B. Facilitating the movement of ions across the membrane C. Synthesizing ATP D. Binding to hormones

B. Facilitating the movement of ions across the membrane

What triggers the release of neurotransmitters into the synaptic cleft? A. Opening of potassium channels B. Opening of voltage-gated calcium channels C. Closing of sodium channels D. Activation of receptor tyrosine kinases

B. Opening of voltage-gated calcium channels

Which of the following is true about phospholipid bilayers? A. They are rigid and inflexible. B. They are impermeable to all ions. C. They can self-assemble in aqueous environments. D. They require energy to maintain their structure.

C. They can self-assemble in aqueous environments.

Which molecule is directly responsible for muscle contraction? A. Acetylcholine B. ATP C. Calcium D. Sodium

C. Calcium

What role does the Golgi apparatus play in membrane trafficking? A. Synthesizing membrane lipids B. Sorting and packaging proteins for transport C. Degrading misfolded proteins D. Generating ATP for active transport

B. Sorting and packaging proteins for transport

Which of the following is true about transmembrane proteins? A. They are peripheral proteins that do not span the membrane. B. They are anchored only to the inner leaflet of the membrane. C. They span the lipid bilayer and may function as channels or receptors. D. They are composed only of hydrophobic amino acids.

C. They span the lipid bilayer and may function as channels or receptors.

Which of the following best describes the role of membrane carbohydrates? A. Providing energy for active transport B. Facilitating membrane fluidity C. Mediating cell-cell recognition and adhesion D. Forming the hydrophobic core of the lipid bilayer

C. Mediating cell-cell recognition and adhesion

Which type of ion channel opens in response to changes in membrane potential? A. Ligand-gated ion channel B. Voltage-gated ion channel C. Mechanosensitive ion channel D. Leak ion channel

B. Voltage-gated ion channel

Which of the following molecules cannot diffuse directly through the lipid bilayer? A. Oxygen B. Carbon dioxide C. Glucose D. Nitrogen

C. Glucose

Which of the following is true about the phospholipid bilayer of the cell membrane? A. The hydrophobic tails face the aqueous environment. B. The hydrophilic heads face the aqueous environment. C. It is composed only of phospholipids and proteins. D. The hydrophilic heads face inward towards each other.

B. The hydrophilic heads face the aqueous environment.

What is the function of gap junctions in animal cells? A. Preventing the passage of molecules between cells B. Allowing direct communication between adjacent cells C. Anchoring cells to the extracellular matrix D. Providing structural support to the plasma membrane

B. Allowing direct communication between adjacent cells

Which of the following is a function of membrane-bound enzymes? A. Synthesizing ATP from ADP and Pi B. Transporting ions across the membrane C. Catalyzing chemical reactions at the membrane surface D. Binding to extracellular ligands

C. Catalyzing chemical reactions at the membrane surface

Which ion is most likely to be involved in generating an action potential in neurons? A. Chloride B. Sodium C. Magnesium D. Phosphate

B. Sodium

Which of the following is involved in vesicle fusion during exocytosis? A. Clathrin B. SNARE proteins C. Ribosomes D. DNA

B. SNARE proteins

Which of the following best describes facilitated diffusion? A. The passive movement of molecules down their concentration gradient with the aid of a transport protein. B. The active movement of molecules against their concentration gradient with the aid of ATP. C. The passive movement of molecules through the lipid bilayer without any protein involvement. D. The active movement of ions across the membrane coupled with the transport of another molecule.

A. The passive movement of molecules down their concentration gradient with the aid of a transport protein.

What is the primary function of ionotropic receptors? A. They directly alter gene expression. B. They directly change ion flow across the membrane. C. They are involved in endocytosis. D. They catalyze the conversion of ATP to cAMP.

B. They directly change ion flow across the membrane.

Which of the following is a characteristic of a carrier protein? A. It forms a continuous pore through the membrane. B. It binds to a specific molecule and undergoes a conformational change. C. It requires ATP to function. D. It is always open and non-selective.

B. It binds to a specific molecule and undergoes a conformational change.

Which process involves the engulfing of large particles by the cell membrane? A. Pinocytosis B. Phagocytosis C. Exocytosis D. Transcytosis

B. Phagocytosis

What type of molecule is most likely to pass through the cell membrane without assistance? A. A small, nonpolar molecule B. A large, polar molecule C. An ion D. A protein

A. A small, nonpolar molecule

Which of the following best describes the function of the Na+/K+ ATPase? A. It maintains the membrane potential by exchanging three sodium ions for two potassium ions. B. It facilitates passive diffusion of sodium and potassium ions. C. It transports glucose into the cell. D. It synthesizes ATP using the energy of ion gradients.

A. It maintains the membrane potential by exchanging three sodium ions for two potassium ions.

What is the main role of caveolae in the plasma membrane? A. They serve as sites for clathrin-mediated endocytosis. B. They are involved in signal transduction and endocytosis. C. They anchor cytoskeletal elements to the membrane. D. They facilitate the movement of large molecules across the membrane.

B. They are involved in signal transduction and endocytosis.

What triggers the opening of ligand-gated ion channels? A. A change in membrane potential B. The binding of a specific ligand C. Mechanical stress on the membrane D. The phosphorylation of the channel

B. The binding of a specific ligand

Which of the following best describes the function of membrane rafts? A. They increase the fluidity of the membrane. B. They are involved in cell signaling and protein sorting. C. They prevent the movement of proteins within the membrane. D. They serve as barriers to the passage of ions.

B. They are involved in cell signaling and protein sorting.

Which of the following processes requires energy in the form of ATP? A. Facilitated diffusion B. Osmosis C. Active transport D. Simple diffusion

C. Active transport

What is the main function of the extracellular matrix (ECM)? A. To regulate ion transport across the membrane B. To provide structural support and regulate cell behavior C. To facilitate intracellular signaling D. To transport oxygen and nutrients to cells

B. To provide structural support and regulate cell behavior

Which of the following proteins is involved in the formation of tight junctions? A. Integrins B. Claudins C. Cadherins D. Collagen

B. Claudins

Which type of transport involves the movement of two substances in the same direction across the membrane? A. Antiport B. Symport C. Uniport D. Facilitated diffusion

B. Symport

What role do integrins play in the plasma membrane? A. They facilitate ion transport across the membrane. B. They mediate cell adhesion to the extracellular matrix. C. They act as receptors for steroid hormones. D. They pump protons into lysosomes.

B. They mediate cell adhesion to the extracellular matrix.

Which type of receptor typically activates intracellular signaling cascades involving second messengers? A. Ionotropic receptor B. G-protein-coupled receptor (GPCR) C. Nuclear receptor D. Enzyme-linked receptor

B. G-protein-coupled receptor (GPCR)

Which of the following is true about membrane potential? A. It is the same across all cell types. B. It is established by the movement of water across the membrane. C. It is primarily maintained by ion gradients across the membrane. D. It is independent of ion channels.

C. It is primarily maintained by ion gradients across the membrane.

What is the role of dynamin in endocytosis? A. To stabilize the clathrin-coated vesicle B. To hydrolyze ATP for vesicle formation C. To pinch off the vesicle from the plasma membrane D. To transport the vesicle to the lysosome

C. To pinch off the vesicle from the plasma membrane

Which of the following molecules is typically involved in the formation of gap junctions? A. Connexins B. Cadherins C. Selectins D. Actin

A. Connexins

Which of the following is true about lipid-anchored proteins? A. They span the entire lipid bilayer. B. They are covalently attached to a lipid molecule within the membrane. C. They freely move within the membrane. D. They are found only on the cytoplasmic side of the membrane.

B. They are covalently attached to a lipid molecule within the membrane.

What is the function of the sodium-glucose cotransporter (SGLT)? A. It transports glucose into cells independently of sodium. B. It uses the sodium gradient to drive glucose uptake into cells. C. It pumps sodium out of the cell in exchange for glucose. D. It transports glucose out of the cell against its concentration gradient.

B. It uses the sodium gradient to drive glucose uptake into cells.

Which of the following is a function of phosphatidylinositol (PI) in the plasma membrane? A. It serves as a precursor for second messengers. B. It stabilizes membrane fluidity. C. It forms the core structure of lipid rafts. D. It acts as a primary ion channel in the membrane.

A. It serves as a precursor for second messengers.

What is the role of SNARE proteins in vesicular transport? A. They coat vesicles during endocytosis. B. They facilitate the fusion of vesicles with target membranes. C. They bind ligands for receptor-mediated endocytosis. D. They transport vesicles along microtubules.

B. They facilitate the fusion of vesicles with target membranes.

Which of the following processes is involved in the degradation of membrane proteins? A. Phagocytosis B. Ubiquitination and proteasomal degradation C. Exocytosis D. Endocytosis followed by lysosomal degradation

D. Endocytosis followed by lysosomal degradation

What is the primary function of desmosomes? A. To allow the passage of ions between cells B. To anchor intermediate filaments to the plasma membrane C. To prevent the movement of molecules between cells D. To facilitate cell-cell communication

B. To anchor intermediate filaments to the plasma membrane

Which of the following ions is most closely associated with the depolarization phase of an action potential? A. Sodium (Na+) B. Potassium (K+) C. Chloride (Cl-) D. Calcium (Ca2+)

A. Sodium (Na+)

Which of the following is not a function of the plasma membrane? A. Protecting the cell from its external environment B. Regulating the passage of substances into and out of the cell C. Storing genetic information D. Facilitating cell signaling

C. Storing genetic information

What type of transport is primarily involved in maintaining the resting membrane potential? A. Simple diffusion B. Secondary active transport C. Facilitated diffusion D. Primary active transport

D. Primary active transport

Which of the following best describes an electrochemical gradient? A. A difference in ion concentration across a membrane B. A combination of a chemical gradient and an electrical gradient C. The movement of molecules against their concentration gradient D. A measure of the membrane's permeability to ions

B. A combination of a chemical gradient and an electrical gradient

What is the primary role of glycoproteins in the plasma membrane? A. Structural support B. Ion transport C. Cell recognition and signaling D. Membrane fluidity regulation

C. Cell recognition and signaling

Which type of cellular junction is primarily involved in anchoring cells to one another? A. Tight junctions B. Gap junctions C. Desmosomes D. Hemidesmosomes

C. Desmosomes

Which type of membrane protein is involved in cell-cell adhesion? A. Transporters B. Enzymes C. Cadherins D. Ion channels

C. Cadherins

What is the primary function of the Na+/K+ ATPase pump? A. To move sodium into the cell and potassium out B. To maintain the concentration gradients of Na+ and K+ across the membrane C. To facilitate the diffusion of water across the membrane D. To generate ATP

B. To maintain the concentration gradients of Na+ and K+ across the membrane

What happens when a ligand binds to an enzyme-linked receptor? A. The receptor opens an ion channel B. The receptor dimerizes and activates its enzymatic function C. The receptor is internalized by endocytosis D. The receptor changes its conformation but remains inactive

B. The receptor dimerizes and activates its enzymatic function

Which of the following is a common characteristic of ion channels? A. They require ATP to function B. They are specific for certain ions C. They are always open D. They can only transport ions out of the cell

B. They are specific for certain ions

Which type of transport involves the movement of water across a semipermeable membrane? A. Diffusion B. Osmosis C. Active transport D. Endocytosis

B. Osmosis

Which molecule typically triggers the opening of ligand-gated ion channels? A. Calcium ions B. Neurotransmitters C. Glucose D. ATP

B. Neurotransmitters

What is the role of peripheral membrane proteins? A. To act as ion channels B. To span the lipid bilayer C. To attach to the membrane temporarily for signaling or structural purposes D. To pump ions across the membrane

C. To attach to the membrane temporarily for signaling or structural purposes

Which of the following best describes the role of phosphatidylinositol in the plasma membrane? A. Structural support B. Cell-cell adhesion C. Signal transduction D. Maintaining membrane fluidity

C. Signal transduction

Which of the following processes is responsible for the uptake of solid particles into the cell? A. Pinocytosis B. Phagocytosis C. Exocytosis D. Simple diffusion

B. Phagocytosis

Which molecule serves as the energy currency of the cell, often used to power active transport? A. Glucose B. ATP C. GTP D. ADP

B. ATP

What is the function of connexins in the plasma membrane? A. To bind to ligands for signal transduction B. To form channels that allow direct communication between adjacent cells C. To act as receptors for neurotransmitters D. To stabilize the membrane structure

B. To form channels that allow direct communication between adjacent cells

Which process describes the movement of molecules from an area of high concentration to an area of low concentration? A. Active transport B. Facilitated diffusion C. Osmosis D. Diffusion

D. Diffusion

Which of the following is true about exocytosis? A. It is a form of passive transport. B. It involves the release of substances from the cell via vesicles. C. It requires the cell to engulf large particles. D. It occurs only in prokaryotic cells.

B. It involves the release of substances from the cell via vesicles.

Which type of membrane receptor is most directly associated with the activation of intracellular signaling cascades? A. G-protein-coupled receptors B. Ion channels C. Nuclear receptors D. Structural proteins

A. G-protein-coupled receptors

Which of the following is true about passive transport? A. It requires energy input from ATP. B. It can only occur in the presence of transport proteins. C. It moves substances against their concentration gradient. D. It moves substances down their concentration gradient.

D. It moves substances down their concentration gradient.

Which of the following best describes the role of calcium ions in cellular signaling? A. Calcium ions act as a primary messenger that binds to receptors on the cell surface. B. Calcium ions enter the cell through ligand-gated channels and activate intracellular enzymes. C. Calcium ions are stored in the Golgi apparatus and released into the cytoplasm during signaling. D. Calcium ions directly bind to DNA to regulate gene expression.

B. Calcium ions enter the cell through ligand-gated channels and activate intracellular enzymes.

Which type of protein spans the entire plasma membrane and is involved in transporting molecules across the membrane? A. Peripheral proteins B. Integral proteins C. G-proteins D. Structural proteins

B. Integral proteins

What is the primary function of receptor tyrosine kinases (RTKs)? A. To transport ions across the membrane B. To phosphorylate specific target proteins after ligand binding C. To act as channels for water and small solutes D. To facilitate vesicular transport

B. To phosphorylate specific target proteins after ligand binding

Which of the following best describes the process of pinocytosis? A. The cell engulfs large particles or entire cells. B. The cell takes in liquid and small solutes by forming vesicles. C. The cell releases substances into the extracellular space. D. The cell transports ions through ion channels.

B. The cell takes in liquid and small solutes by forming vesicles.