Chap04 - Cell Structure.pdf

Chapter 4

Cell Structure: A Tour of the Cell

Cell:

A basic unit of living matter separated from

its environment by a plasma membrane.

The smallest structural unit of life.

Microscopy

First observations of cells were made with

light microscopes:

Robert Hooke (1665): Used primitive microscope to

observe cork (dead plant cells). Coined the word

cell.

Anton van Leeuenhoeck (1670s): Made single lens

microscopes. First person to observe live cells

under microscope: “animalcules” (protists) in

water, red blood cells, sperm, bacteria, and insect

eggs.

Theodor Schwann (1830s): Observed harder to view

animal cells. Called cells “elementary particles” of

both plants and animals.

Cell Theory: Developed in late 1800s.

1. All living organisms are made up of one or

more cells.

2. The smallest living organisms are single

cells, and cells are the functional units of

multicellular organisms.

3. All cells arise from preexisting cells.

Microscope FeaturesMagnification:

Increase in apparent size of an object.

Ratio of image size to specimen size.

Resolving power: Measures clarity of image.

Ability to see fine detail.

Ability to distinguish two objects as separate.

Minimum distance between 2 points at which

they can be distinguished as separate and

distinct.

Microscopes

Light Microscopes: Earliest microscopes

used.

Lenses pass visible light through a specimen.

Magnification: Highest possible from 1000 X to

2000 X.

Resolving power: Up to 0.2 mm (1 mm = 1/1000

mm).

Types of Microscope

Electron Microscopes: Developed in 1950s.

Electron beam passes through specimen.

Magnification: Up to 200,000 X.

Resolving power: Up to 0.2 nm (1nm =

1/1’000,000 mm).

Two types of electron microscopes:

1. Scanning Electron Microscope: Used to study

cell or virus surfaces.

2. Transmission Electron Microscope: Used to

study internal cell structures.

Components of All Cells:

1. Plasma membrane: Separates cell contents

from outside environment. Made up of

phospholipid bilayers and proteins.

2. Cytoplasm: Liquid, jelly-like material inside

cell.

3. Ribosomes: Necessary for protein synthesis.

Procaryotic versus Eucaryotic Cells

Feature Procaryotic Eucaryotic

Organisms Bacteria All others (animals, plants,

fungi, and protozoa)

Nucleus Absent Present

DNA One chromosome Multiple chromosomes

Size Small (1-10 um) Large (10 or more um)

Membrane Absent Present (mitochondria,Bound golgi, chloroplasts, etc.)Organelles

Division Rapid process Complex process

(Binary fission) (Mitosis)

Relative Sizes of Structures

1 nanometer (10-9 m) water molecule

10 nanomters (10-8 m) small protein

100 nanometers (10-7 m) HIV virus

1 micron (10-6 m) cell vacuole

10 microns (10-5 m) bacterium

100 microns (10-4 m) large plant cell

1 millimeter (10-3 m) single cell embryo

Relative Sizes of Procaryotic and

Eucaryotic Cells and Viruses

Relative Sizes of Cells and Other Objects

Prokaryotic Cells

Bacteria and blue-green algae.

Small size: Range from 1- 10 micrometers in length.

About one tenth of eukaryotic cell.

No nucleus: DNA in cytoplasm or nucleoid region.

Ribosomes are used to make proteins

Cell wall: Hard shell around membrane

Other structures that may be present:

• Capsule: Protective, outer sticky layer. May be used for

attachment or to evade immune system.

• Pili: Hair-like projections (attachment)

• Flagellum: Longer whip-like projection (movement)

Procaryotic Cells: Lack a Nucleus and

other Membrane Bound Organelles

Eucaryotic Cells

Include protist, fungi, plant, and animal cells.

Nucleus: Protects and houses DNA

Membrane-bound Organelles: Internal

structures with specific functions.

Separate and store compounds

Store energy

Work surfaces

Maintain concentration gradients

Membrane-Bound Organelles of Eucaryotic

Cells

Nucleus

Rough Endoplasmic Reticulum (RER)

Smooth Endoplasmic Reticulum (SER)

Golgi Apparatus

Lysosomes

Vacuoles

Chloroplasts

Mitochondria

Eucaryotic Cells: Typical Animal Cell

Eucaryotic Cells: Typical Plant Cell

Nucleus

Structure

Double nuclear membrane (envelope)

Large nuclear pores

DNA (genetic material) is combined with histones

and exists in two forms:

• Chromatin (Loose, threadlike DNA, most of cell life)

• Chromosomes (Tightly packaged DNA. Found only

during cell division)

Nucleolus: Dense region where ribosomes are made

Functions

House and protect cell’s genetic information (DNA)

Ribosome synthesis

Structure of Cell Nucleus

Endoplasmic Reticulum (ER)

“Network within the cell”

Extensive maze of membranes that branches

throughout cytoplasm.

ER is continuous with plasma membrane and

outer nucleus membrane.

Two types of ER:




Flat, interconnected, rough membrane sacs

“Rough”: Outer walls are covered with

ribosomes.

Ribosomes: Protein making “machines”.

May exist free in cytoplasm or attached to ER.

RER Functions:

Synthesis of cell and organelle membranes.

Synthesis and modification of proteins.

Packaging, and transport of proteins that are

secreted from the cell.

• Example: Antibodies


Network of interconnected tubular smooth

membranes.

“Smooth”: No ribosomes

SER Functions:

Synthesis of phospholipids, fatty acids, and

steroids (sex hormones).

Breakdown of toxic compounds (drugs, alcohol,

amphetamines, sedatives, antibiotics, etc.).

Helps develop tolerance to drugs and alcohol.

Regulates levels of sugar released from liver into

the blood

Calcium storage for cell and muscle contraction.

Golgi Apparatus

Stacks of flattened membrane sacs that may be

distended in certain regions. Sacs are not

interconnected.

First described in 1898 by Camillo Golgi (Italy).

Works closely with the ER to secrete proteins.

Golgi Functions:

Receiving side receives proteins in transport vesicles from ER.

Modifies proteins into final shape, sorts, and labels proteins for proper transport.

Shipping side packages and sends proteins to cell membrane for export or to other parts of the cell.

Packages digestive enzymes in lysosomes.

The Golgi Apparatus: Receiving,

Processing, and Shipping of Proteins

Lysosomes

Small vesicles released from Golgi containing at least 40 different digestive enzymes, which can break down carbohydrates, proteins, lipids, and nucleic acids.

Optimal pH for enzymes is about 5

Found mainly in animal cells.

Lysosome Functions:

Molecular garbage dump and recycler of

macromolecules (e.g.: proteins).

Destruction of foreign material, bacteria, viruses,

and old or damaged cell components.

Digestion of food particles taken in by cell.

After cell dies, lysosomal membrane breaks down,

causing rapid self-destruction.

Lysosomes: Intracellular Digestion

Lysosomes, Aging, and Disease

As we get older, our lysosomes become leaky,

releasing enzymes which cause tissue damage and

inflammation.

Example: Cartilage damage in arthritis.

Steroids or cortisone-like anti-inflammatory agents

stabilize lysosomal membranes, but have other

undesirable effects (affect immune function).

Diseases from “mutant” lysosome enzymes are

usually fatal:

Pompe’s disease: Defective glycogen breakdown in liver.

Tay-Sachs disease: Defective lipid breakdown in brain.

Common genetic disorder among Jewish people.

Vacuoles

Membrane bound sac.

Different sizes, shapes, and functions:

Central vacuole: In plant cells. Store starch, water,

pigments, poisons, and wastes. May occupy up to

90% of cell volume.

Contractile vacuole: Regulate water balance, by

removing excess water from cell. Found in many

aquatic protists.

Food or Digestion Vacuole: Engulf nutrients in

many protozoa (protists). Fuse with lysosomes to

digest food particles.

Central Vacuole in a Plant Cell

Interactions Between Membrane

Bound Organelles of Eucaryotic Cells

Chloroplasts

Site of photosynthesis in plants and algae.

CO2 + H2O + Sun Light -----> Sugar + O2

Number may range from 1 to over 100 per

cell.

Disc shaped structure with three different

membrane systems:

1. Outer membrane: Covers chloroplast surface.

2. Inner membrane: Contains enzymes needed to

make glucose during photosynthesis. Encloses

stroma (liquid) and thylakoid membranes.

3. Thylakoid membranes: Contain chlorophyll,

green pigment that traps solar energy. Organized

in stacks called grana.

Chloroplasts Trap Solar Energy and

Convert it to Chemical Energy

Chloroplasts

Contain their own DNA, ribosomes, and

make some proteins.

Can divide to form daughter chloroplasts.

Type of plastid: Organelle that produces and

stores food in plant and algae cells.

Other plastids include:

Leukoplasts: Store starch.

Chromoplasts: Store other pigments that give

plants and flowers color.

Mitochondria (Sing. Mitochondrion)

Site of cellular respiration:

Food (sugar) + O2 -----> CO2 + H2O + ATP

Change chemical energy of molecules into the

useable energy of the ATP molecule.

Oval or sausage shaped.

Contain their own DNA, ribosomes, and

make some proteins.

Can divide to form daughter mitochondria.

Structure: Inner and outer membranes.

Intermembrane space

Cristae (inner membrane extensions)

Matrix (inner liquid)

Mitochondria Harvest Chemical Energy From Food

Origin of Eucaryotic Cells

Endosymbiont Theory: Belief that

chloroplasts and mitochondria were at one

point independent cells that entered and

remained inside a larger cell.

Both organelles contain their own DNA

Have their own ribosomes and make their own

proteins.

Replicate independently from cell, by binary

fission.

Symbiotic relationship

Larger cell obtains energy or nutrients

Smaller cell is protected by larger cell.

The Cytoskeleton

Complex network of thread-like and tube-

like structures.

Functions: Movement, structure, and structural

support.

Three Cytoskeleton Components:

1. Microfilaments: Smallest cytoskeleton fibers.

Important for:

Muscle contraction: Actin & myosin fibers in

muscle cells

“Amoeboid motion” of white blood cells

Components of the Cytoskeleton are

Important for Structure and Movement

Three Cytoskeleton Components:

2. Intermediate filaments: Medium sized fibers

Anchor organelles (nucleus) and hold cytoskeleton

in place.

Abundant in cells with high mechanical stress.

3. Microtubules: Largest cytoskeleton fibers.

Found in:

Centrioles: A pair of structures that help move

chromosomes during cell division (mitosis and

meiosis).

Found in animal cells, but not plant cells.

Movement of flagella and cilia.

Typical Animal Cell

Cilia and Flagella

Projections used for locomotion or to move

substances along cell surface.

Enclosed by plasma membrane and contain

cytoplasm.

Consist of 9 pairs of microtubules surrounding

two single microtubules (9 + 2 arrangement).

Flagella: Large whip-like projections.

Move in wavelike manner, used for locomotion.

Example: Sperm cell

Cilia: Short hair-like projections.

Example: Human respiratory system uses cilia to

remove harmful objects from bronchial tubes and

trachea.

Structure of Eucaryotic Flagellum

Cell Surfaces

A. Cell wall: Much thicker than cell membrane,

(10 to 100 X thicker).

Provides support and protects cell from lysis.

Plant and algae cell wall: Cellulose

Fungi and bacteria have other polysaccharides.

Not present in animal cells or protozoa.

Plasmodesmata: Channels between adjacent plant

cells form a circulatory and communication system

between cells.

Sharing of nutrients, water, and chemical messages.

Plasmodesmata: Communication

Between Adjacent Plant Cells

Cell SurfacesB. Extracellular matrix: Sticky layer of glycoproteins

found in animal cells.

Important for attachment, support, protection, and

response to environmental stimuli.

Junctions Between Animal Cells:

Tight Junctions: Bind cells tightly, forming a leakproof

sheet. Example: Between epithelial cells in stomach lining.

Anchoring Junctions: Rivet cells together, but still allow

material to pass through spaces between cells.

Communicating Junctions: Similar to plasmodesmata in

plants. Allow water and other small molecules to flow

between neighboring cells.

Different Animal Cell Junctions

Important Differences Between

Plant and Animal Cells

Plant cells Animal cells

Cell wall None (Extracellular matrix)

Chloroplasts No chloroplasts

Large central vacuole No central vacuole

Flagella rare Flagella more usual

No Lysosomes Lysosomes present

No Centrioles Centrioles present

Differences Between Plant and Animal Cells

Animal Cell

Plant Cell

Typical Plant Cell

Summary of Eucaryotic Organelles

Function: Manufacture

Nucleus

Ribosomes

Rough ER

Smooth ER

Golgi Apparatus

Function: Breakdown

Lysosomes

Vacuoles

Summary of Eucaryotic Organelles

Function: Energy Processing

Chloroplasts (Plants and algae)

Mitochondria

Function: Support, Movement, Communication

Cytoskeleton (Cilia, flagella, and centrioles)

Cell walls (Plants, fungi, bacteria, and some

protists)

Extracellular matrix (Animals)

Cell junctions

Chap04 - Cell Structure.pdf

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