Cell Membrane Structure and Fluidity

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Questions and Answers

What effect do shorter tails have on transmembrane proteins?

They decrease the fluidity of the membrane.

They increase the stability of the membrane.

They allow for easier movement of transmembrane proteins. (correct)

They enhance protein binding to the cytoskeleton.

How does the presence of double bonds affect lipid behavior in the membrane?

They create a kink in the lipid tail, enhancing membrane fluidity. (correct)

They make lipids more rigid.

They decrease the overall number of lipids.

They prevent lipids from forming bilayers.

What is the role of cholesterol in cell membranes?

It acts solely as a barrier against toxins.

It promotes the movement of lipids only.

It stabilizes membranes, affecting fluidity based on temperature. (correct)

It enhances the fluidity of membranes at all temperatures.

What percentage of membrane proteins may be restricted in their movement?

Between 10% and 70% Signup and view all the answers

Where does the synthesis of lipids primarily occur in eukaryotic cells?

In the cytosol and smooth endoplasmic reticulum. Signup and view all the answers

What is the first destination for most transmembrane proteins after synthesis?

Endoplasmic reticulum membrane. Signup and view all the answers

What is glycosylation?

The attachment of carbohydrates to proteins or lipids. Signup and view all the answers

What is N-linked glycosylation?

Attaching carbohydrates to the nitrogen atom of asparagine. Signup and view all the answers

Which molecules can pass through a phospholipid bilayer most easily?

Gases and small uncharged molecules. Signup and view all the answers

What happens when cells face temperature changes?

They may alter their lipid composition. Signup and view all the answers

What define the selectivity of the plasma membrane?

The hydrophobic interior and membrane proteins. Signup and view all the answers

What defines the process of active transport?

It requires energy to transport substances against their concentration gradient. Signup and view all the answers

What typically characterizes the permeability of ions across the membrane?

Very low permeability. Signup and view all the answers

How does HbA1c test benefit diabetes management?

It measures the average blood sugar control over three months. Signup and view all the answers

What is the primary structure that makes up the framework of biological membranes?

Phospholipid bilayer Signup and view all the answers

Which type of membrane protein is physically embedded in the phospholipid bilayer?

Transmembrane proteins Signup and view all the answers

What characteristic of phospholipids contributes to their arrangement in biological membranes?

Amphipathic nature Signup and view all the answers

What is required for the 'flip-flop' movement of lipids between the leaflets of a membrane?

Flippase activity Signup and view all the answers

What distinguishes lipid rafts from the rest of the membrane?

High concentration of cholesterol Signup and view all the answers

Which factor does NOT affect the fluidity of membranes?

Presence of enzymes Signup and view all the answers

Which type of protein is attached to the membrane via a covalent bond to a lipid molecule?

Lipid-anchored proteins Signup and view all the answers

How do lipids primarily move within the membrane?

Lateral movement Signup and view all the answers

What best describes the Fluid-Mosaic Model of membranes?

Dynamic structure with elements able to move relative to one another Signup and view all the answers

Which property of membrane lipids contributes to their behavior as a fluid structure?

Shorter acyl tails lead to reduced interaction Signup and view all the answers

What happens to animal cells in a hypertonic solution?

They shrink and undergo crenation Signup and view all the answers

What process prevents osmotic lysis in plant cells when taking up water?

Cell wall Signup and view all the answers

Which type of transport protein uses energy to move solutes against their concentration gradient?

Active transporters Signup and view all the answers

What is the primary role of Na+/K+ -ATPase in cells?

Generates electrochemical gradients Signup and view all the answers

What characterizes receptor-mediated endocytosis?

It is driven by specific receptors in the plasma membrane Signup and view all the answers

Which of the following best describes osmosis?

Water moves to balance solute concentrations across a membrane Signup and view all the answers

What is plasmolysis in plant cells?

Plasma membrane detachment from the cell wall Signup and view all the answers

How do contractile vacuoles help freshwater protists like Paramecium?

Maintain constant cell volume by expelling water Signup and view all the answers

What is a characteristic of gated channels in cell membranes?

Transition from open to closed states controlled by ligands Signup and view all the answers

Which of the following describes secondary active transport?

It relies on gradients created by primary active transport Signup and view all the answers

What is the function of transport proteins in membranes?

Facilitate movement of ions and hydrophilic molecules Signup and view all the answers

What is the definition of osmosis?

The movement of water across a selectively permeable membrane Signup and view all the answers

What does active transport require that passive transport does not?

Cellular energy input Signup and view all the answers

Study Notes

Membrane Structure

The cell membrane is a phospholipid bilayer
The phospholipid bilayer consists of two layers of phospholipids
Phospholipids are amphipathic, with hydrophilic heads and hydrophobic tails
The hydrophilic heads face the aqueous environment, while the hydrophobic tails face each other inside the membrane
Cell membranes also contain proteins and carbohydrates
The two layers of the phospholipid bilayer are asymmetrical: they contain different amounts of lipids, proteins, and carbohydrates

Fluidity of Membranes

The cell membrane is a fluid structure meaning that phospholipids and proteins can move laterally within the membrane
Membrane fluidity is influenced by fatty acid tail length, degree of saturation, and cholesterol content
Shorter fatty acid tails and unsaturation increase membrane fluidity
Cholesterol can stabilize membranes at high temperatures and decrease fluidity at low temperatures

Synthesis of Membrane Components

Lipids are synthesized in the smooth endoplasmic reticulum (ER)
Fatty acid building blocks are made by enzymes in the cytosol
Membrane proteins are synthesized on ribosomes and inserted into the ER membrane
Most proteins destined for the plasma membrane first go to the ER
Glycosylation occurs in the ER and Golgi apparatus

Overview of Membrane Transport

Biological membranes are selectively permeable, allowing some molecules to pass through while blocking others
Membrane transport can be passive or active
Passive transport does not require energy: simple diffusion and facilitated diffusion
Active transport requires energy to move molecules against their concentration or electrochemical gradient

Proteins That Carry Out Membrane Transport

Transport proteins are transmembrane proteins that provide a pathway for the movement of ions and molecules across membranes
Channels form open passageways for facilitated diffusion
Transporters bind to a solute and undergo a conformational change to move them across the membrane
Transporters can be uniporters, symporters, or antiporters

Exocytosis and Endocytosis

Exocytosis and endocytosis are processes used to transport large molecules and polysaccharides
Exocytosis involves the packaging of material inside the cell into vesicles and their release into the extracellular medium
Endocytosis involves the invagination of the plasma membrane to form vesicles that bring substances into the cell
There are three types of endocytosis: receptor-mediated endocytosis, pinocytosis, and phagocytosis

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Description

Explore the intricate structure and dynamics of the cell membrane. This quiz covers phospholipid bilayers, membrane fluidity, and the impact of various components on membrane stability. Test your knowledge about the synthesis of membrane components and their functions.