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Quizzes > Science > Biology

Test Your Knowledge: Integral vs Peripheral Proteins Quiz

Think you know integral and peripheral membrane proteins? Take the quiz and prove it!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art coral background cell membrane cross section integral proteins spanning bilayer, peripheral proteins on surface

Use this quiz to compare integral vs peripheral proteins, see where each sits in the membrane, tell how they attach, and sort examples like transmembrane, lipid-anchored, and surface-bound. Check your weak spots before an exam and keep practicing with molecule partners and cell membrane practice .

Which of the following best describes an integral membrane protein?
A protein loosely attached via ionic bonds
A protein attached by a lipid anchor only
A peripheral enzyme bound by hydrogen bonds
A protein that spans the membrane with hydrophobic regions
Integral membrane proteins contain hydrophobic segments that span the lipid bilayer, making them inseparable from the membrane without detergents. They often have several transmembrane helices that interact with the hydrophobic core. This property distinguishes them from peripheral proteins that attach via surface interactions.
Peripheral membrane proteins are most commonly associated with the membrane through which interactions?
Covalent attachment to phospholipids
Hydrophobic transmembrane helices
Electrostatic interactions and hydrogen bonds
Disulfide bonds with integral proteins
Peripheral proteins associate with the membrane surface through non-covalent electrostatic interactions and hydrogen bonds, often with lipid head groups or integral proteins. These interactions allow them to be removed by changing ionic strength or pH. They do not penetrate the hydrophobic core of the bilayer.
Which experimental method can extract peripheral proteins without solubilizing the lipid bilayer?
Sonication
Detergent treatment
Chaotropic agents
High-salt wash
High-salt washes disrupt electrostatic interactions between peripheral proteins and lipid head groups without solubilizing the membrane lipid bilayer. This method removes peripheral proteins while leaving integral proteins in the membrane intact. Detergents or chaotropic agents would disrupt the bilayer and remove integral proteins.
Which type of amino acids is most commonly found in the membrane-spanning region of integral proteins?
Charged polar amino acids
Aromatic amino acids only
Hydrophobic nonpolar amino acids
Glycosylated amino acids
The membrane-spanning regions of integral proteins are enriched in hydrophobic nonpolar amino acids such as leucine, isoleucine, and valine to interact with the lipid core. Polar or charged residues are unfavorable in the hydrophobic interior. These hydrophobic segments often form alpha helices across the membrane.
Beta-barrel proteins are a class of which membrane protein type?
Lipid-anchored proteins
Peripheral proteins
Cytosolic proteins
Integral proteins
Beta-barrel proteins are integral membrane proteins that form barrel-like structures stabilized by hydrogen bonds between beta-strands. They are commonly found in the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Their transmembrane segments are beta-strands rather than alpha-helices.
Glycosylphosphatidylinositol (GPI)-anchored proteins are classified as which category?
Integral monotopic proteins
Integral polytopic proteins
Soluble secreted proteins
Peripheral lipid-anchored proteins
GPI-anchored proteins are covalently linked to a glycosylphosphatidylinositol moiety, which anchors them to the membrane surface. They are considered lipid-anchored peripheral proteins because they attach through a lipid tether rather than spanning the membrane. They can be released by specific phospholipases.
A membrane protein with seven alpha-helical transmembrane segments is characteristic of what class of proteins?
ABC transporters
G-protein-coupled receptors
Ion channels
Beta-barrel porins
G protein-coupled receptors (GPCRs) characteristically contain seven transmembrane alpha-helices. These helices allow them to span the membrane seven times and transmit signals across the lipid bilayer. This 7TM architecture distinguishes GPCRs from other membrane proteins.
Which reagent is most appropriate for solubilizing integral membrane proteins while maintaining their tertiary structure?
Sodium dodecyl sulfate (SDS)
Urea
High pH buffer
Triton X-100
Triton X-100 is a nonionic mild detergent that solubilizes lipid bilayers and integral membrane proteins while preserving their tertiary structure. It disrupts lipid-lipid and lipid-protein interactions without denaturing most proteins. Ionic detergents like SDS would denature proteins.
For a type I single-pass transmembrane protein, which terminus is oriented toward the cytoplasm?
Both termini
Neither terminus
C-terminus
N-terminus
Type I single-pass transmembrane proteins have an N-terminal signal sequence that is cleaved in the lumen, leaving the N-terminus extracellular and the C-terminus in the cytoplasm. The stop-transfer anchor sequence halts translocation and orients the C-terminus in the cytosol. This orientation is consistent across type I proteins.
Amphitropic proteins differ from peripheral proteins in that they:
Always require lipid anchors
Are released by pH change only
Can exist both soluble and membrane-bound
Are permanently embedded in the membrane
Amphitropic proteins can exist both in a soluble form in the cytosol and bound reversibly to membranes, depending on regulatory factors like phosphorylation or calcium. Peripheral proteins are generally membrane-associated only, not found freely in solution. This reversible dual localization is unique to amphitropic proteins.
What is the primary role of a stop-transfer anchor sequence in membrane protein biogenesis?
Initiates polypeptide translocation
Directs proteins to mitochondria
Acts as a glycosylation signal
Terminates translocation and anchors the protein
A stop-transfer anchor sequence is a hydrophobic segment that halts translocation of the nascent polypeptide in the translocon and anchors the protein in the membrane. It determines the topology of integral membrane proteins by fixing the transmembrane orientation. Without this sequence, the protein would be fully translocated or mislocalized.
Which detergent is most likely to denature proteins while effectively disrupting membranes?
Octyl glucoside
CHAPS
Triton X-100
Sodium dodecyl sulfate (SDS)
Sodium dodecyl sulfate (SDS) is an ionic detergent that disrupts both lipid bilayers and protein structure, leading to protein denaturation. It is commonly used in SDS-PAGE to linearize proteins. Nonionic detergents are used when maintaining protein structure is desired.
To distinguish integral membrane proteins from peripheral proteins, which treatment would you apply?
Protease treatment of intact cells
Lipase digestion
0.1 M sodium carbonate pH 11 and centrifugation
Mild salt wash
The use of alkaline sodium carbonate at high pH strips peripheral proteins from membranes by disrupting electrostatic interactions while leaving integral proteins embedded in the lipid bilayer. After centrifugation, integral proteins remain in the membrane pellet, whereas peripheral proteins are in the supernatant. This method is a classic approach to distinguish the two classes.
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Study Outcomes

  1. Differentiate Integral vs Peripheral Proteins -

    Compare the structural characteristics and membrane interactions of integral and peripheral proteins to solidify your grasp of their distinct roles.

  2. Identify Membrane Protein Locations -

    Pinpoint where integral and peripheral proteins reside within and on the cell membrane, from transmembrane segments to surface associations.

  3. Classify Integral and Peripheral Membrane Proteins -

    Categorize examples of integral lipid-anchored, transmembrane, and peripheral proteins based on their anchoring mechanisms and functions.

  4. Analyze Functional Roles -

    Evaluate how integral and peripheral proteins contribute to transport, signaling, and structural integrity within the lipid bilayer.

  5. Apply Knowledge to Quiz Questions -

    Leverage your understanding of integral protein vs peripheral protein differences to answer questions like "which of the following is correct regarding integral proteins?" with confidence.

Cheat Sheet

  1. Core Structural Differences -

    Integral vs peripheral proteins differ in how they associate with the lipid bilayer: integral proteins penetrate the hydrophobic core via transmembrane α-helices or β-barrels, while peripheral proteins attach loosely to membrane surfaces through ionic or hydrogen bonds. A simple mnemonic "I-LOVE-OIL" (Integral LOVEs hydrOphobic Interactions, Peripheral prefers Ionic Links) can help you recall that integral proteins interact deeply with oil-like lipid tails. (Source: Alberts et al., Molecular Biology of the Cell)

  2. Hydrophobicity and Membrane Insertion -

    Integral membrane proteins have hydrophobic amino acid stretches long enough (about 20 - 25 residues) to span the bilayer; you can estimate the free energy change (ΔG) for insertion using the Wimley-White scale. In contrast, peripheral proteins lack these hydrophobic cores and bind via charged or polar side chains, which makes them extractable with mild salt solutions. (Source: White and Wimley, Annual Review of Biophysics)

  3. Functional Roles in Transport and Signaling -

    Integral membrane proteins serve as channels, carriers, and receptors - think of aquaporin letting water flow or GPCRs transmitting hormones - while peripheral proteins often act as modulators (e.g., kinases, G-protein subunits) on the membrane surface. Remember: integral proteins are the "gates and sensors," peripheral proteins are the "switches and amplifiers." (Source: Lodish et al., Molecular Cell Biology)

  4. Experimental Extraction Techniques -

    To isolate integral proteins, researchers use detergents (e.g., SDS or Triton X-100) that disrupt lipid interactions; peripheral proteins, however, are removed by increasing ionic strength or changing pH. A quick lab tip: high-salt buffers "shake off" peripheral proteins without dissolving the bilayer. (Source: Methods in Enzymology)

  5. Localization in Membrane Domains -

    Integral and peripheral membrane proteins often cluster in specialized regions like lipid rafts - cholesterol-rich microdomains that facilitate signal transduction and protein sorting. Visualize rafts as "floating platforms" where integral receptors and peripheral adaptors congregate for efficient communication. (Source: Simons & Ikonen, Nature Reviews Molecular Cell Biology)

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