Chapter 3 Anatomy and Physiology

Cell

basic unit of life and the smallest structure capable of performing all life function

List the general parts of a cell

The three major parts common to most cells are:

1. Plasma membrane (cell membrane)

2. Cytoplasm

3. Nucleus

Relate and explain the four main functions of cells.

The four major functions are:

1. Cell metabolism and energy use

2. Synthesis of molecules

3. Communication

4. Reproduction and inheritance

Plasma Membrane (Cell Membrane)

The outer boundary of the cell that separates the cell from its external environment and controls movement into and out of the cell

Functions of the Plasma Membrane

• Forms the cell boundary

• Controls entry and exit of substances

• Enables cell communication

• Allows cells to recognize one another

Cytoplasm

The material located between the plasma membrane and nucleus where most cell activities occur

Nucleus

The control center of the cell containing DNA, which regulates protein synthesis and cell activities.

Organelle

A specialized structure inside the cell that performs a specific function.

Cell Metabolism and Energy Use

Cell metabolism includes all chemical reactions occurring within a cell

Key Concepts of Cell Metabolism

• Energy released from one reaction powers another reaction.

• Nutrient breakdown releases energy.

• Energy is used for:

  • molecule synthesis

  • muscle contraction

  • cellular work

• Heat is released during metabolism and helps maintain body temperature.

Metabolism

All chemical reactions in the body or cell.

Energy Transfer

Energy released by one reaction is used to drive another reaction.

Synthesis of Molecules

Cells produce molecules such as:

• proteins

• nucleic acids

• lipids

• Cells produce molecules such as:

  • proteins

  • nucleic acids

  • lipids

Protein

Large molecules used for structure, transport, enzymes, and signaling.

Nucleic Acids

DNA and RNA molecules involved in genetic information.

Lipids

Fats and fat-like molecules important in membranes and energy storage.

Communication

Cells communicate using:

• chemical signals

• electrical signals

Key Concepts

• Nerve cells send chemical signals.

• Muscle cells respond by contracting or relaxing.

Reproduction and Inheritance

Cells divide to produce new cells containing identical genetic information.

Key Concepts

• Most cells contain a complete copy of DNA.

• DNA determines structure and function.

• Cell division allows growth and repair.

• Gametes transfer genetic information to offspring.

Plasma Membrane Structure

• Lipid bilayer made mainly of phospholipids and cholesterol

• Contains proteins

Plasma Membrane Function

Functions

• Cell boundary

• Controls movement of substances

• Cell recognition

• Communication

Nucleus Structure

• Surrounded by nuclear envelope

• Contains chromatin (DNA + proteins)

• Contains nucleolus/nucleoli

Nucleus Functions

• Controls cell activities

• DNA regulates protein synthesis

Ribosome Structure

Made of ribosomal RNA and proteins.

Ribosome Function

Site of protein synthesis.

Rough Endoplasmic Reticulum (Rough ER) Structure

Membranous sacs with attached ribosomes.

Rough Endoplasmic Reticulum (Rough ER) Function

Synthesizes proteins and transports them to the Golgi apparatus.

Smooth Endoplasmic Reticulum (Smooth ER) Function

• Manufactures lipids and carbohydrates

• Detoxifies chemicals

• Stores calcium

Golgi Apparatus

Modifies, packages, and distributes proteins and lipids.

Lysosome

Contains digestive enzymes for intracellular digestion.

Peroxisome

• Breaks down fatty acids and amino acids

• Breaks down hydrogen peroxide

Proteasomes

Break down proteins in the cytoplasm.

Mitochondria

Major site of ATP production when oxygen is available.

Centrioles

• Organize microtubules

• Help during cell division

• Form basal bodies of cilia and flagella

Cilia

Move materials over the cell surface.

Flagellum

Propels sperm cells.

Microvilli

Increase surface area for:

• absorption

• secretion

• sensory reception

What parts are common to most cells?

• a plasma membrane

• cytoplasm

• a nucleus

• organelles within the cytoplasm

Explain the four characteristic functions of the cell.

1. Metabolism and Energy Use

Cells perform chemical reactions that release and use energy.

2. Synthesis of Molecules

Cells produce proteins, nucleic acids, and lipids.

3. Communication

Cells communicate using chemical and electrical signals.

4. Reproduction and Inheritance

Cells divide to form new cells and pass genetic information to offspring.

Relate the kinds of microscopes used to study cells

Cells and tissues are too small to be seen clearly with the naked eye, so microscopes are required to study them. The two major categories are:

1. Light microscopes

2. Electron microscopes

Resolution

The ability to distinguish two nearby objects as separate objects.

Microscope

An instrument used to magnify and visualize structures too small to be seen by the naked eye.

Light Microscope

A microscope that uses visible light to produce an image.

Key Facts

• Resolution limit ≈ 0.1 μm

• Good for viewing cells and tissues

• Commonly used for biopsy specimens

• Specimens often require stains or fluorescent antibodies

Electron Microscope

A microscope that uses beams of electrons instead of light.

Key Facts

• Resolution limit ≈ 0.1 nm

• Used to see structures much smaller than cells

• Produces highly detailed images

Types of Electron Microscopes

Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
Atomic Force Microscope (AFM)

Transmission Electron Microscope (TEM)

An electron microscope in which electrons pass through the specimen.

Characteristics

• Highest magnification

• Thin specimen sections required

• Excellent internal detail

• Specimen thickness: 0.01–0.15 μm
  

Best For

Viewing internal structures such as:

• organelles

• membranes

• nuclear pores

Scanning Electron Microscope (SEM)

An electron microscope in which electrons reflect off the specimen surface.

Characteristics

• Produces 3D-like images

• Greater depth of focus

• Lower magnification than TEM

• Excellent surface detail

Best For

Viewing:

• cell surfaces

• tissue topography

• external structures

Atomic Force Microscope (AFM)

A microscope that scans surfaces with a tiny mechanical probe to create a 3D surface map.

Characteristics

• Combines:

  • TEM’s high resolution

  • SEM’s surface visualization

• Can examine samples under more natural physiological conditions

• Produces black-and-white images unless false color is added

Why tissues are stained

Most tissues are:

• colorless

• transparent when thinly sliced

Stains or fluorescent antibodies are used so structures become visible

Which cell features can be seen with a light microscope? With electron microscopes?

Light Microscope

Can see:

• whole cells

• tissues

• nuclei

• large organelles

• general tissue structure
  

Electron Microscopes

Can see:

• very small organelles

• membranes

• nuclear pores

• molecular-level structures

• surface details in high resolution

Plasma Membrane 3.3

The outermost structure of the cell that separates intracellular substances from extracellular substances.

Intracellular

Inside the cell; refers to substances located within the cytoplasm

Extracellular

Outside the cell; refers to substances outside the plasma membrane.

Membrane Potential

The electrical charge difference across the plasma membrane caused by unequal ion distribution

Glycolipid

A carbohydrate attached to a lipid molecule.

Glycoprotein

A carbohydrate attached to a protein molecule.

Glycocalyx

A coating on the outer surface of the plasma membrane made of glycolipids, glycoproteins, and carbohydrates.

Functions of the Plasma Membrane

1. Boundary Function
2. Structural Support
3. Attachment Function
4. Cell Recognition & Communication
5. Selective Transport

1. Boundary Function

The membrane separates:

• intracellular substances
  from

• extracellular substances

This allows the cell to maintain a controlled internal environment.

2. Structural Support

The membrane:

• encloses cell contents

• supports the cell structure

3. Attachment Function

The membrane attaches:

• cells to the extracellular environment

• cells to neighboring cells

This is important for tissue formation.

4. Cell Recognition & Communication

The plasma membrane allows cells to:

• recognize each other

• communicate chemically

Important for:

• immune responses

• signaling

• coordination between cells

5. Selective Transport

The membrane controls:

• what enters the cell

• what leaves the cell

This helps maintain homeostasis.

Chemical Components of the Plasma Membrane

The plasma membrane consists mainly of:

1. Lipids

2. Proteins

3. Small amounts of carbohydrates

1. Lipids

Main membrane lipids:

• phospholipids

• cholesterol

Percentage

Lipids account for about 45–50% of membrane weight.

Functions

• form membrane structure

• create barrier

• provide flexibility

2. Proteins

Proteins also make up about 45–50% of membrane weight.

Functions

• transport

• communication

• receptors

• enzymes

• cell recognition

3. Carbohydrates

Carbohydrates make up:

• about 4–8% of the membrane

Characteristics

• found only on outer surface

• combine with lipids and proteins

Glycocalyx

• coats the outer membrane surface

• helps with cell recognition

• helps communication

• interacts with extracellular materials

How Membrane Potential Forms

The membrane regulates ion movement.

Distribution of charges:

• more positive ions outside

• more negative ions/proteins inside
  SO….

• outside of membrane = more positive

• inside of membrane = more negative

Importance of Membrane Potential

Membrane potential is important for:

• nerve impulses

• muscle contraction

• normal cell function

Membrane Lipids

Lipids that form the structural framework of the plasma membrane.

Main membrane lipids:

• phospholipids

• cholesterol

Phospholipid

A lipid with:

• a polar hydrophilic head

• nonpolar hydrophobic tails

Lipid Bilayer

A double layer of phospholipid molecules forming the plasma membrane

Hydrophilic

“Water-loving”; attracted to water.

Hydrophobic

“Water-fearing”; repelled by water.

Fluid-Mosaic Model

A model describing the plasma membrane as flexible and dynamic, with proteins suspended in a fluid lipid bilayer.

Cholesterol

A lipid located between phospholipids that stabilizes the plasma membrane and influences membrane fluidity.

Functions of the Lipid Bilayer

• forms membrane structure

• creates a barrier

• allows flexibility

• supports membrane proteins

Location of Cholesterol

• interspersed among phospholipids

• about one-third of membrane lipids

Structure of Cholesterol

Hydrophilic Hydroxyl Group

• Extends near phospholipid heads.
  

Hydrophobic Portion

• Lies within the hydrophobic membrane interior
  

Function of Cholesterol

• limits phospholipid movement

• stabilizes the membrane

• influences membrane fluidity

Characteristics of the Fluid-Mosaic Model

The plasma membrane:

• is not rigid

• is not static

• is flexible

• changes shape and composition over time

Important Consequences of Membrane Fluidity

1. Distribution of Molecules

Fluidity allows molecules to move and distribute throughout the membrane.

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2. Membrane Repair

Damaged phospholipids can reassemble and seal small breaks.

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3. Membrane Fusion

Fluid membranes can fuse with one another.

Integral Membrane Protein

A protein deeply embedded within the lipid bilayer and often spanning the membrane.

Peripheral Membrane Protein

A protein attached to the inner or outer membrane surface.

Marker Molecule

A membrane molecule used for cell identification and recognition.

Transport Protein

A membrane protein that moves ions or molecules across the membrane.

Receptor Protein

A membrane protein that binds chemical signals and triggers cellular responses.

Enzyme

A protein that catalyzes chemical reactions.

Integral Proteins Characteristics

• penetrate lipid bilayer

• may extend completely through membrane

• contain hydrophobic and hydrophilic regions

Peripheral Proteins Characteristics

• attached to membrane surface

• do not extend through membrane

• may bind to phospholipid heads or integral proteins

Functions of Membrane Proteins

Membrane proteins function as:

1. Marker molecules

2. Attachment proteins

3. Transport proteins

4. Receptor proteins

5. Enzymes

1. Marker Molecules

Allow cells to:

• identify other cells

• recognize foreign substances

Examples:

• sperm recognizing oocyte

• immune system recognizing bacteria

2. Attachment Proteins

Allow cells to attach to:

• other cells

• extracellular molecules

Cadherins

Attach cells to other cells.

Integrins

Attach cells to extracellular molecules.

3. Transport Proteins

Move substances across membrane.

Three major classes:

1. Channel proteins

2. Carrier proteins

3. ATP-powered pumps

Channel Proteins

Form tiny membrane channels.

Leak Channels

Always open.

Ligand-Gated Channels

Open/close when ligands bind.

Voltage-Gated Channels

Open/close when membrane potential changes.