Cell Biology: Membranes Structure and Function

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Questions and Answers

What is the primary function of the plasma membrane?

To store genetic information

To act as a barrier and control passage of materials (correct)

To synthesize proteins

To provide energy to the cell

Cholesterol in the cell membrane decreases its fluidity.

False

What components make up the lipid bilayer of the cell membrane?

Phospholipids, glycoproteins, and cholesterol

The lipid bilayer consists of a glycerol head that is and 2 fatty acid tails that are .

hydrophilic; hydrophobic Signup and view all the answers

Match the components of the cell membrane with their functions:

Phospholipids = Create the bilayer structure Cholesterol = Regulates membrane fluidity Proteins = Facilitate communication and transport Carbohydrates = Attach to the outer surface for recognition Signup and view all the answers

Which of the following substances can easily penetrate the cell membrane?

Oxygen Signup and view all the answers

The plasma membrane is composed of 55% proteins and 42% lipids.

True Signup and view all the answers

What role do negatively charged carbohydrates play in the cell membrane?

They attach to the outer surface for cell recognition. Signup and view all the answers

Membranes are described as ___________ structures because they are not fixed and can change shape.

dynamic Signup and view all the answers

What is the thickness range of the plasma membrane?

7.5 to 10 nanometers Signup and view all the answers

Which type of protein spans the membrane and provides structural channels?

Integral proteins Signup and view all the answers

Peripheral proteins are embedded across the entire membrane.

False Signup and view all the answers

What are glycoproteins primarily used for in the cell membrane?

Cell recognition Signup and view all the answers

The presence of __________ within the membrane enhances its fluidity.

unsaturated hydrocarbon tails Signup and view all the answers

Match the protein type with its function:

Channel Protein = Allows substances to move across the membrane Carrier Protein = Selectively interacts with specific molecules Receptor Protein = Specifically shaped for a specific molecule Enzymatic Protein = Catalyzes specific reactions Signup and view all the answers

Which of the following is NOT a function of membrane proteins?

Storage of genetic information Signup and view all the answers

Membrane fluidity is beneficial for proper membrane function.

True Signup and view all the answers

What happens to membrane enzymes when solidification occurs?

Enzymes may become inactivated. Signup and view all the answers

The cell membrane is primarily composed of __________ and proteins.

phospholipids Signup and view all the answers

What maintains the structure of the membrane through weak interactions?

Weak hydrophobic interactions Signup and view all the answers

Study Notes

Membranes: Structure and Function

Membranes are dynamic, acting as barriers, receiving information and moving.
Membranes surround the cell.
They are selectively permeable, controlling what goes in and out.
They participate in intracellular communication.

Plasma Membrane

Elastic structure measuring 7.5 to 10 nanometers thick.
Separates cell’s interior from the exterior environment.

Membrane Composition

Lipids (42%)
- Phospholipids (25%)
- Cholesterol (13%)
- Glycolipids (4%)
Proteins (55%)
Carbohydrates (3%)

Membrane Lipids

Form a stable, low energy bilayer.
Amphipathic: contain both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts.
Hydrophobic compounds reach equilibrium quickly within the bilayer.
Lipids form effective barriers for some compounds.

Phospholipids

Consist of a glycerol head (polar and hydrophilic) and two fatty acid 'tails' (non-polar and hydrophobic).

Cholesterol

Steroid nucleus is highly fat soluble.
Regulates membrane permeability to water-soluble substances like ions and glucose.
Contributes to membrane fluidity.

Membrane Proteins

Integral proteins (intrinsic)
- Span the membrane.
- Provide structural channels or pores.
- Can act as enzymes or receptors for molecules like peptide hormones.
Peripheral proteins (extrinsic)
- Embedded in one side of the membrane.
- Associated by weak electrostatic bonds to membrane proteins or lipids.

Functions of Membrane Proteins

Transporters: move substances across the membrane.
Enzymes: catalyze specific reactions.
Cell surface receptors: bind to signaling molecules.
Cell surface identity markers: allow recognition by the immune system.
Cell-to-cell adhesion proteins: connect cells together.
Attachments to the cytoskeleton: provide structural support.

Integral Protein Functions

Channel Proteins: allow specific substances to move across the membrane.
Carrier Proteins: selectively interact with specific molecules or ions to facilitate their transport across the membrane.
Cell Recognition Proteins (Glycoproteins): allow the cell to be recognized by the immune system.
Receptor Proteins: interact with specific molecules based on their shape.
Enzymatic Proteins: catalyze specific reactions within the membrane.

Membrane Carbohydrates

Primarily attached to the outer surface of the membrane as:
- Glycoproteins: (most abundant)
- Glycolipids: (1/10 of the amount)

Functions of Membrane Carbohydrates

Attach cells to each other.
Act as receptor substances.
Facilitate immune system recognition of foreign cells.
Give most cells a negative surface charge, affecting interactions with regulatory molecules.

Why Membrane Fluidity is Crucial

Membrane fluidity is essential for proper function.
Solidification can lead to permeability changes and enzyme deactivation.
Unsaturated fatty acid tails with kinks prevent close packing of phospholipids, enhancing fluidity.

Membrane Movement

Weak hydrophobic interactions hold the membrane together.
Membrane lipids and some proteins can drift laterally within the membrane.
Molecules rarely flip transversely (flip-flop) across the membrane because hydrophilic parts would have to cross the hydrophobic core.

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Description

This quiz covers the essential concepts of cell membranes, including their structure, composition, and functional roles. Test your knowledge on the dynamic nature of membranes, their selective permeability, and the types of lipids and proteins involved. Ideal for students studying cell biology and related topics.