A Tour of the Cell

Chapter 6

Overview: The Importance of Cells

Cell Theory: All organisms are made of cells

The cell is the simplest collection of matter that can live

Cells

All cells have several basic features in common

They are bounded by a plasma membrane

They contain a semifluid substance called the cytosol (cytoplasm is the physical area between membrane and nucleus which contains the cytosol)

They contain chromosomes made of DNA

They have ribosomes

The Cell

Prokaryotic cells

Do not contain a nucleus or other membrane bound organelles

Have their DNA located in a region called the nucleoid

Two Types of Cells

Pili

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella(a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

0.5 µm

Prokaryotic Cell

Eukaryotic cells

Contain a true nucleus, bounded by a membranous nuclear envelope

Contain many other specialized membrane bound organelles

Are generally quite a bit bigger than prokaryotic cells

Two Types of Cells

In animal cells but not plant cells:•Lysosomes•Centrioles•Flagella (in some plant sperm)•ECM•Desmosomes, tight junctions, gap junctions

Eukaryotic Cells: Animal

In plant cells but not animal cells:•Chloroplasts•Central vacuole and tonoplast•Cell wall•Plasmodesmata

Eukaryotic Cells: Plant

Endomembrane system is a related series of membrane bound structures responsible for protein and lipid synthesis. Includes:

Plasma/cell membrane

Nuclear membrane

Endoplasmic reticulum

Golgi apparatus

Lysosomes

Vacuoles and vesicles

Endomembrane System

Outside of cell

Hydrophilicregion

HydrophobicregionHydrophilicregion

Phospholipid

Proteins

0.1 µm

Inside of cell

Plasma membrane: Selective Barrier

Carbohydrate

Pore complexes Nuclear lamina

Nucleus

NucleusNucleolus

Nuclear envelope:

Nuclear porePorecomplex

1 µm

1 µm

0.25 µm

Nucleus and its Envelope: Contains DNA

Ribosomes ER Cytosol

Endoplasmic reticulum (ER)

Free ribosomes

Bound ribosomes

Largesubunit

Smallsubunit

TEM showing ER and ribosomes Diagram of a ribosomerRNA and proteins

0.5 µm

Ribosomes: Protein Factories

Smooth ER

Rough ER

ER lumenCisternae

RibosomesTransport vesicle

Transitional ER200 µm

Endoplasmic reticulum (ER): Series of Membranes

Rough ER:

Contains bound ribosomes so manufactures proteins

These proteins often destined to be exported from cell

Smooth ER:

No ribosomes so no protein synthesis

Lipid synthesis such as making fatty acids, steroids

Metabolizes carbohydrates

Detoxification of drugs by adding hydroxyl groups (makes water soluble)

Roles of Rough and Smooth ER

Golgiapparatus

cis facereceiving”

Cisternae

trans face“shipping” side

TEM of Golgi apparatus

0.1 0 µm

5

3

Golgi apparatus: “Post Office” of the Cell

Lysosome

1 µm

1 µ m

Vesicle containingdamaged mitochondrion

Digestion

Food vacuole

Plasma membraneLysosome

Digestiveenzymes

Phagocytosis: lysosome digesting food Autophagy: lysosome breaking down damaged organelle

Lysosome

Digestion

Lysosome

Lysosomes: Digestive Enzyme Packets

Central vacuole

Tonoplast

Centralvacuole

5 µm

Plant Cell Vacuole

Intermembrane spaceOuter

membrane

Freeribosomesin the mitochondrialmatrix

MitochondrialDNA

InnermembraneCristae

Matrix

100 µm

Mitochondrion: Site of Cellular Respiration (ATP Synthesis)

Endosymbiosis?“living within”

Granum

Chloroplast

ChloroplastDNA

RibosomesStromaInner and outermembranes

Thylakoid1 µm

Chloroplast: Site of Photosynthesis

Also endosymbiosis?

Network of fibers in cytoplasm that organize and anchors organelles and gives structural support

3 types of cytoskeleton

Microtubules

Microfilaments

Intermediate filaments

Cytoskeleton

StructureThickest of 3 types, hollow

Made of tubulin

Dynamic structure

Microtubules

Microtubules Function

Provides organelle tracks

Moves chromosomes during cell division

Forms structure of locomotive appendages cilia and flagella

StructureThinnest of 3 types, solid

Made of actin

Twisted, double chain

Dynamic stucture

Microfilaments

Function

Interacts with myosin for muscle contraction

Creates cleavage furrow during cell division

Responsible for gel-sol state

Pseudopodia

Cytoplasmic streaming

Microfilaments

• Structure

• Intermediate in size

• Made of keratin

• Permanent structure

Intermediate Filaments

• Function

• Organelle anchor

• Comprises nuclear lamina

• Desmosomes

Intermediate Filaments

Plasma membrane

1 µmCentral vacuole

Plant cell walls

Plasmodesmata

Plant Cell Walls: Made of cellulose

Tight junctions prevent fluid from moving across a layer of cells

Tight junction

0.5 µm

1 µm

Spacebetweencells

Plasma membranesof adjacent cells

Gap junction

Tight junctions

0.1 µm

Intermediatefilaments

Desmosome

Gapjunctions

.

“Communicating”

TIGHT JUNCTIONS

DESMOSOMES

GAP JUNCTIONS

Intercellular Junctions in Animal Tissues

“Rivets”

“Seals”