Cell Membrane Structure and Function

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Questions and Answers

Which type of protein is firmly embedded in the lipid bilayer and is not easily extracted?

Peripheral proteins

Transmembrane proteins (correct)

Integral proteins (correct)

Glycoproteins

What role does cholesterol play in the cell membrane?

Acts as a receptor for signaling

Forms the cell coat

Regulates fluidity and stabilizes the bilayer (correct)

Enhances membrane permeability

What is the function of glycolipids and glycoproteins in the cell membrane?

Enhance membrane fluidity

Act as channels for ions

Facilitate passive transport

Project from the membrane to form the glycocalyx (correct)

Which process involves the cell expelling waste products?

Exocytosis Signup and view all the answers

How do integral proteins interact with microfilaments?

They provide structural support Signup and view all the answers

What kind of transport requires receptors and energy?

Selective transport Signup and view all the answers

Which of the following describes phagocytosis?

Engulfing of solid particles Signup and view all the answers

What is a primary function of the cell coat?

Providing adhesive functions for cell-to-cell interaction Signup and view all the answers

What is the primary function of the cell membrane?

Control the movement of substances in and out of the cell Signup and view all the answers

Which of the following correctly describes the structure of phospholipids in the cell membrane?

Hydrophilic heads face away from water forming a bilayer Signup and view all the answers

How thick is the cell membrane typically measured?

7.5-10 nm Signup and view all the answers

What characteristic appearance does the cell membrane exhibit when viewed under electron microscopy?

Trilaminar appearance Signup and view all the answers

What types of molecules primarily compose the cell membrane?

Lipid molecules, proteins, and carbohydrates Signup and view all the answers

Which part of the phospholipid molecule is hydrophilic?

The head Signup and view all the answers

What is the primary component that influences the fluidity of the cell membrane?

Cholesterol Signup and view all the answers

Which of the following structures is NOT considered a part of the cell membrane?

Ribosomes Signup and view all the answers

What is the primary function of mitochondria in cells?

To provide the cell with ATP through aerobic respiration Signup and view all the answers

Which layer of the mitochondrion helps increase surface area for energy production?

Inner membrane Signup and view all the answers

Which type of microscopy is used to visualize the detailed structure of mitochondria?

Electron microscopy Signup and view all the answers

What component of mitochondria allows for the replication of their DNA?

Mitochondrial matrix Signup and view all the answers

How do mitochondria adapt their number in cells?

Through division in accordance with energy needs Signup and view all the answers

What appearance do renal tubules exhibit under light microscopy due to their mitochondrial content?

Acidophilic Signup and view all the answers

What is a characteristic of the outer membrane of mitochondria?

It is smooth and lacks folds. Signup and view all the answers

Which of the following stains is routinely used for light microscopy to visualize cells?

Hematoxylin & Eosin (H & E) Signup and view all the answers

Study Notes

Cell Membrane

The outer limiting membrane surrounding the cell
Also known as plasma membrane or plasmalemma
Thickness: 7.5 to 10 nm, visible only by electron microscopy (E.M.)
Trilaminar appearance in E.M. with two electron-dense lines (black) separated by an electron-lucent one (white)

Molecular Structure of Cell Membrane

Composed of lipid molecules, proteins, and carbohydrates

Lipid Molecules

Phospholipids: consist of a hydrophilic head and a hydrophobic tail
Form a double layer (bilayer) with hydrophobic tails directed toward the middle and hydrophilic heads facing water
Cholesterol: located between phospholipid molecules, regulating the fluidity and stabilizing the phospholipid bilayer

Protein Molecules

Integral proteins
- Firmly embedded in the lipid bilayer
- Not easily extracted
- Transmembrane proteins: span the lipid bilayer, attached to microfilaments on the cytoplasmic side for fixation, act as channels
Peripheral proteins
- Loosely attached to the outer or inner membrane surfaces
- Easily extracted

Carbohydrate Molecules

Glycolipids and glycoproteins
Project from the external surface of the membrane, forming the Cell Coat or Glycocalyx

Functions of Cell Membrane

Exchange of materials
- Passive diffusion: for gases and ions, according to concentration gradient
- Active transport: for amino acids, glucose, and fatty acids, requiring enzymes and energy
- Selective transport: for hormones, drugs, and bacteria, requiring receptors and energy
Endocytosis:
- Phagocytosis: for solid particles (cell eating), example: macrophages engulfing bacteria
- Pinocytosis: for fluids (cell drinking)
- Receptor-mediated endocytosis: for large molecules like protein hormones and drugs, requires receptors (integral proteins)
Exocytosis: opposite to phagocytosis, the cell expels waste products
Functions of Cell Coat
- Adhesive function: for adjacent cells
- Role in immunity: recognizing self and foreign cells
- Participation in the formation of the basement membrane

Mitochondria

Membranous organelles containing enzymes specialized for energy production (ATP)
Powerhouse of the cell
Size and shape: variable, can be elongated, rod-shaped, or spherical
Number: highly variable depending on the activity of the cell (e.g., liver cells have numerous mitochondria, while lymphocytes have very few)
Sites: highly mobile, localizing at sites of maximum energy requirement (e.g., between myofibrils in cardiac muscle cells)
The number of mitochondria is modified by mitochondrial division

Routine Stain for Light Microscopy (LM)

Hematoxylin & Eosin (H&E)
- Hematoxylin (H): basic (alkaline), blue color, reacts with acidic structures inside the cell (DNA in the nucleus, RNA in ribosomes and RER)
- Eosin (E): acidic, red color, reacts with basic structures inside the cell, typically the cytoplasm which is rich in mitochondria
Cytoplasm rich in ribosomes and RER is basophilic (e.g., plasma cell)
Cytoplasm rich in mitochondria is acidophilic (e.g., renal tubules)

Light Microscopy (LM) of Mitochondria

H&E: mitochondria are responsible for the acidophilic cytoplasm
Succinic dehydrogenase enzyme activity: succinate dehydrogenase is an enzyme of the Krebs citric acid cycle exclusive to mitochondria

Electron Microscopy (EM) of Mitochondria

Double-membranous organelle with four compartments:
- Outer membrane: smooth, no folds
- Inner membrane: forms complex folds called cristae, increased in more active cells
- Intermembranous space
- Mitochondrial matrix: contains mitochondrial DNA and ribosomes

Functions of Mitochondria

Provide the cell with ATP: aerobic respiration occurs within the matrix and on the inner membrane to produce energy
Mitochondrial matrix contains one or more circular strands of DNA, allowing division and increase in number based on energy need of the cell

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Description

This quiz explores the composition and structure of the cell membrane, also known as the plasma membrane. It covers the roles of lipid molecules, proteins, and carbohydrates in maintaining membrane integrity and function. Test your knowledge on the fundamental concepts of cellular membranes.