Biomembrane Composition and Proteins

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson
Download our mobile app to listen on the go
Get App

Questions and Answers

Which components are found in biomembranes?

  • A protein monolayer, carbohydrates, and glycoproteins
  • A lipid bilayer, embedded proteins, and nucleic acids
  • A lipid bilayer, embedded proteins, glycoproteins, and glycolipids (correct)
  • A phospholipid monolayer, embedded carbohydrates, and proteins

Integral membrane proteins are characterized by which of the following?

  • They consist of an extracellular domain, a transmembrane domain, and a cytosolic domain. (correct)
  • They are weakly associated with the polar head groups of lipids.
  • They are only found on the extracellular side of the plasma membrane.
  • They are attached to the membrane via ionic interactions.

How do lipid-anchored proteins associate with the biomembrane?

  • Via covalent bonds to lipids within one leaflet of the membrane (correct)
  • By attaching to integral membrane proteins on the membrane surface
  • Through direct covalent bonds with the hydrophilic head groups of phospholipids
  • By weak interactions with the carbohydrate chains extending into the extracellular space

What is the primary function of flippases in the cell membrane?

<p>To move phospholipids between leaflets of the biomembrane (A)</p> Signup and view all the answers

Which statement accurately describes the function of glycoproteins and glycolipids in the biomembrane?

<p>They allow for cell recognition and interaction. (B)</p> Signup and view all the answers

What is a critical requirement for the growth of biomembranes?

<p>The synthesis and incorporation of new phospholipids, sphingolipids, and cholesterol (C)</p> Signup and view all the answers

How are macromolecules with hydrophobic properties typically synthesized for incorporation into biomembranes?

<p>They are synthesized as water-soluble precursors. (B)</p> Signup and view all the answers

Where does fatty acid synthesis primarily occur in the cell?

<p>In the cytosol (D)</p> Signup and view all the answers

What role does acetyl-CoA carboxylase play in fatty acid synthesis?

<p>It converts acetyl-CoA to malonyl-CoA. (B)</p> Signup and view all the answers

Where are enzymes located that catalyze the reaction between fatty acyl-CoA molecules and glycerol 3-phosphate during phosphoglyceride synthesis?

<p>Embedded in the membrane of the smooth endoplasmic reticulum (D)</p> Signup and view all the answers

What is the initial product generated after the reaction between fatty acyl-CoA molecules and glycerol 3-phosphate during phosphoglyceride synthesis, and where is it inserted?

<p>Phosphatidic acid, inserted into the cytosolic leaflet of the ER membrane (C)</p> Signup and view all the answers

What modification can fatty acids undergo via desaturase enzymes that act on phosphoglycerides?

<p>Acquisition of double bonds (A)</p> Signup and view all the answers

Which cellular location is the site of sphingolipid synthesis?

<p>Smooth endoplasmic reticulum and Golgi apparatus (B)</p> Signup and view all the answers

What is the correct order of events in sphingolipid synthesis?

<p>Palmatoyl-CoA binds to serine, a second fatty acyl-CoA binds to the product to form ceramide, a head group is added in the Golgi, and sphingolipids are sent to their final destination. (A)</p> Signup and view all the answers

Where are cholesterol precursors synthesized, and where are they converted into cholesterol?

<p>Synthesized in the cytosol; converted in the smooth ER membrane. (D)</p> Signup and view all the answers

What are the primary mechanisms by which phospholipids and cholesterol are transported to their final destinations after being synthesized in the smooth ER?

<p>Vesicle formation and fusion, transport via binding proteins, and transfer at membrane contact sites (D)</p> Signup and view all the answers

Which of the following factors affects the rate of simple diffusion across a biomembrane?

<p>Temperature, magnitude of the concentration gradient, and hydrophobicity of the molecule (A)</p> Signup and view all the answers

How does temperature affect cell membrane permeability in simple diffusion?

<p>Generally, increasing temperature increases membrane permeability due to increased movement of phospholipids. (B)</p> Signup and view all the answers

What distinguishes protein-mediated transport from simple diffusion?

<p>Protein-mediated transport involves specific membrane proteins. (B)</p> Signup and view all the answers

What is the function of ATP-powered pumps in membrane transport?

<p>To move molecules against their concentration gradient using energy from ATP (B)</p> Signup and view all the answers

Compared to transporters, what is a distinguishing characteristic of ion channels?

<p>Higher rate of ion transport (D)</p> Signup and view all the answers

A cell needs to import glucose rapidly when its external concentration is low. Which type of transporter would be most effective?

<p>A symporter that moves glucose along with an ion down its concentration gradient (A)</p> Signup and view all the answers

An antiporter is a membrane transport protein that moves:

<p>Two different molecules in opposite directions. (A)</p> Signup and view all the answers

What is the defining characteristic of facilitated transport?

<p>It involves the use of integral membrane proteins to move molecules down their concentration gradients. (D)</p> Signup and view all the answers

How does active transport differ from co-transport?

<p>Active transport uses ATP-powered pumps, while co-transport uses the movement of one molecule down its gradient to power the transport of another against its gradient. (C)</p> Signup and view all the answers

A researcher discovers a new membrane protein that transports only one type of molecule down its concentration gradient. Which type of transporter is this most likely to be?

<p>A uniporter (D)</p> Signup and view all the answers

Which of the following is a characteristic of membrane proteins that span the lipid bilayer?

<p>They often have hydrophobic amino acids in the region that interacts with the lipid bilayer. (B)</p> Signup and view all the answers

What is the role of the signal recognition particle (SRP) in the synthesis of transmembrane proteins?

<p>It binds to the signal sequence of the growing polypeptide chain and directs it to the ER membrane. (D)</p> Signup and view all the answers

How do biomembranes maintain their asymmetry?

<p>Through the use of flippases, floppases, and scramblases, which selectively move lipids. (A)</p> Signup and view all the answers

A protein is synthesized with a cleavable N-terminal signal sequence, but also contains a 'stop-transfer' sequence. What is likely to be its final orientation in the ER membrane?

<p>It will span the membrane once, with the N-terminus in the ER lumen. (C)</p> Signup and view all the answers

What is the role of scramblases in the synthesis of biomembranes?

<p>They randomly distribute phospholipids between leaflets, eliminating membrane asymmetry. (A)</p> Signup and view all the answers

Which of the following best describes how cholesterol affects membrane fluidity?

<p>It increases fluidity at low temperatures and decreases fluidity at high temperatures. (D)</p> Signup and view all the answers

A mutation in a flippase gene prevents the protein from functioning. What would be the most likely consequence for a cell with this mutation?

<p>Inability to establish and maintain membrane lipid asymmetry. (D)</p> Signup and view all the answers

A researcher treats cells with a drug that inhibits the enzyme acetyl-CoA carboxylase. What is the most likely effect on fatty acid synthesis?

<p>Decreased levels of malonyl-CoA and reduced fatty acid synthesis (B)</p> Signup and view all the answers

In cells that are actively synthesizing membrane lipids, where would you expect to find the highest concentration of flippases?

<p>In the Golgi apparatus and endoplasmic reticulum (ER) membranes (C)</p> Signup and view all the answers

What would be the consequence of a cell lacking desaturase enzymes?

<p>Increased membrane rigidity due to a lack of double bonds in fatty acids (C)</p> Signup and view all the answers

A liver cell synthesizes cholesterol at a high rate. Which organelle would you expect to be particularly well-developed in this cell?

<p>Smooth endoplasmic reticulum (B)</p> Signup and view all the answers

In a series of experiments, a cell's membrane is found to be importing a molecule against its concentration gradient, but this import stops when a similar molecule flowing down its concentration gradient is no longer available. Which type of transport is responsible?

<p>Co-transport (D)</p> Signup and view all the answers

Flashcards

Biomembrane Composition

Biomembranes consist of a lipid bilayer and embedded proteins, glycoproteins, and glycolipids.

Integral Membrane Proteins

Proteins that span the plasma membrane, with extracellular, transmembrane, and cytosolic domains.

Lipid-Anchored Proteins

Proteins covalently bound to lipids within one leaflet, anchored to the hydrophobic core.

Peripheral Proteins

Proteins attached to phospholipid head groups, integral proteins, or lipid-anchored proteins, often linked to the cytoskeleton or extracellular matrix.

Signup and view all the flashcards

Flippases

Membrane proteins that facilitate the movement of phospholipids between leaflets of the biomembrane.

Signup and view all the flashcards

Glycoproteins

Integral membrane proteins covalently bound to carbohydrates.

Signup and view all the flashcards

Glycolipids

Membrane lipids covalently bound to carbohydrates.

Signup and view all the flashcards

Biomembrane Growth

Biomembranes are dynamic structures. New lipids must be synthesized and incorporated into existing membranes.

Signup and view all the flashcards

Fatty Acid Synthesis

Fatty acids are synthesized in the cytosol from acetyl groups in acetyl-CoA, involving fatty acid synthase.

Signup and view all the flashcards

Sphingolipid Synthesis

Occurs in the smooth ER, involving palmatoyl-CoA, serine, and the Golgi apparatus for sphingolipid formation.

Signup and view all the flashcards

Cholesterol Synthesis

Cholesterol precursors are synthesized in the cytosol and converted into cholesterol by enzymes in the ER membrane.

Signup and view all the flashcards

Lipid Transport

Membrane lipids and cholesterol are transported to final destinations via vesicles, binding proteins, or contact sites.

Signup and view all the flashcards

Membrane Transporters

Membrane protein complexes that facilitate the movement of molecules across cell membranes.

Signup and view all the flashcards

Simple Diffusion

Movement across a membrane down a concentration gradient without assistance.

Signup and view all the flashcards

Temperature Impact

Membrane permeability increases at low temperatures, membranes can be damaged, becomes highly permeable once thawed.

Signup and view all the flashcards

ATP-powered pumps

Membrane proteins that use the energy from ATP hydrolysis to move ions or molecules against their concentration gradients.

Signup and view all the flashcards

Ion Channels

Membrane proteins that form pores or channels through which specific ions can flow down their electrochemical gradients, with high transport rates.

Signup and view all the flashcards

Transporters

Membrane proteins that facilitate the movement of specific molecules across the membrane, typically at rates slower than ion channels.

Signup and view all the flashcards

Uniporter

Transports one molecule at a time.

Signup and view all the flashcards

Symporter

Transports two molecules in the same direction.

Signup and view all the flashcards

Antiporter

Transports two molecules in opposite directions.

Signup and view all the flashcards

Facilitated Transport

Movement down concentration gradients via membrane proteins.

Signup and view all the flashcards

Active Transport

Movement against concentration gradients using ATP-powered pumps.

Signup and view all the flashcards

Co-transport

Movement of one molecule against its concentration gradient, coupled with another moving down its gradient.

Signup and view all the flashcards

Study Notes

Biomembranes Composition

  • Biomembranes primarily consist of a lipid bilayer with embedded proteins, glycoproteins, and glycolipids

Membrane Proteins

  • Proteins associate with the membrane in three main ways: integral, lipid-anchored, and peripheral

Integral Membrane Proteins

  • Span the plasma membrane
  • Include an extracellular, transmembrane, and cytosolic domain

Lipid-Anchored Proteins

  • Covalently bound to lipids in one leaflet of the membrane
  • These are anchored to the hydrophobic core

Peripheral Proteins

  • Attach to hydrophilic phospholipid head groups, integral membrane proteins, or lipid-anchored proteins
  • Connect the membrane to the cytoskeleton or extracellular matrix

Phospholipid Transfer

  • Phospholipids do not readily transfer between leaflets
  • Flippases are membrane proteins that move them

Types of Flippases

  • There are three main types; flippases require ATP

Glycoproteins

  • Glycoproteins are integral membrane proteins covalently bound to carbohydrates

Glycolipids

  • Glycolipids are membrane lipids covalently bound to carbohydrates

Carbohydrate Chains

  • Carbohydrate chains extend into the extracellular space

Cell Recognition

  • Glycolipids and glycoproteins facilitate cell recognition

Biomembrane Dynamics

  • Biomembranes are dynamic structures that grow and retract based on cellular needs

Biomembrane Growth Requirements

  • Biomembrane growth requires the synthesis and incorporation of new phospholipids, sphingolipids, and cholesterol

Hydrophobic Challenges

  • The hydrophobic nature poses a challenge such that macromolecules are synthesized as water-soluble precursors

Precursor Incorporation

  • Precursors are incorporated into the biomembrane where enzymes modify them into their mature form

Fatty Acid Synthesis

  • Fatty acids are synthesized in the cytosol from two-carbon acetyl groups in acetyl-CoA
  • Initial acetyl-CoA binds to fatty acid synthase

Acetyl-CoA Carboxylase

  • Converts other acetyl-CoA molecules to malonyl-CoA, a three-carbon molecule
  • Malonyl-CoA is added to initial acetyl-CoA bound to fatty acid synthase which releases a carbon to form an acetyl group

Fatty Acid Growth

  • Growth continues via malonyl-CoA addition until a full fatty acid is produced

Fatty Acyl-CoA

  • Fatty acid converts to fatty acyl-CoA in the cytosol

Smooth ER Enzymes

  • Enzymes in the smooth ER catalyze the reaction between two fatty acyl-CoA molecules and glycerol 3-phosphate

Phosphatidic Acid

  • Generates phosphatidic acid, inserted into the cytosolic leaflet of the ER membrane

Phosphoglyceride

  • Head groups are added to phosphatidic acid to generate phosphoglyceride

Desaturase Enzymes

  • Fatty acids get double bonds from desaturase enzymes on phosphoglycerides

Sphingolipid Synthesis Location

  • Sphingolipid synthesis occurs in the smooth ER

Palmatoyl-CoA Role

  • Palmatoyl-CoA (a 16-carbon fatty acyl CoA) enters the ER and binds to serine

Ceramide Formation

  • A second fatty acyl CoA binds to palmatoyl-serine to form ceramide

Golgi Function

  • Ceramide goes to the Golgi, where a head group is added to form a sphingolipid

Sphingolipid Destination

  • Sphingolipids are sent from the Golgi to their final destinations in the cell

Cholesterol Synthesis Location

  • Cholesterol precursors are synthesized in the cytosol

Precursor Location

  • Precursors embed in the cytosolic leaflet of the smooth ER membrane

ER Membrane Enzymes

  • Enzymes in the ER membrane convert precursors into cholesterol

Transport Mechanisms

  • Transport that is achieved through vesicles, phospholipids or cholesterol, and proteins at biomembrane contact sites

Vesicle Formation

  • Vesicles form from the smooth ER and fuse with the target biomembrane

Lipids Transport

  • Phospholipids or cholesterol are transported through the cytosol by binding proteins

Membrane Contact Sites

  • Proteins at contact sites facilitate transfer between membranes

Final Destination

  • Further modifications occur once at the final destination

Simple Diffusion Factors

  • Rate is affected by temperature, concentration gradient, biomembrane surface area, molecule hydrophobicity, and molecule size

Protein-Mediated Transporters

  • Protein-mediated transport is categorized by the direction molecules move

Facilitated Transport

  • Facilitated transport moves molecules down their concentration gradients using integral membrane proteins, including uniporters and ion channels

Active Transport

  • Active transport moves molecules against their concentration gradient using ATP-powered pumps

Co-Transport

  • Co-transport moves one molecule against its concentration gradient while another moves down its concentration gradient
  • Performed by symporters and antiporters

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser