UNIT III – CELL STRUCTURE & FUNCTION

• Hillis – Ch 4,5• Baby Campbell – Ch 4,5• Big Campbell – Ch 6,7,11

I. DISCOVERY OF CELLS

• History of Microscopes Anton van Leeuwenhoek

Robert Hooke

• Cell Theory All living things are made of cells. Cells are the smallest working unit. All cells come from pre-existing cells through cell division.

I. DISCOVERY OF CELLS, cont.

• Types of Microscopes Compound Light Microscope

MagnificationResolutionAdvances in light microscopy

include o Confocalo Fluorescento Phase Contrasto Super-resolution

Electron MicroscopeScanning Electron

Microscope (SEM)Transmission Electron

Microscope (TEM)

I. DISCOVERY OF CELLS, cont.

• Cell Size o Metabolic needs impose

both upper & lower limits on cell size

o How small?Must have enough space for

DNA, enzymesMycoplasma sp. - < 1 μm

o How large?Surface Area to Volume RatioAdaptations

II. CELL TYPES• Prokaryotic Cells

Typically smaller than euks

BacteriaKingdom Kingdom

No true nucleus – DNA found as a single chromosome in region called nucleoid

II. CELL TYPES, cont• Prokaryotic Cells

II. CELL TYPES, cont

• Eukaryotic Cells Larger, more complex Contain true nucleus, membrane-

bound organelles suspended in cytosol

Composed of Nucleus Ribosomes Endomembrane System

o ERo Golgi Apparatuso Lysosomeso Vacuoles

Mitochondria/Chloroplasts Peroxisomes Cytoskeleton

III. EUKARYOTIC CELL STRUCTURES

_____________ Cell

_______________ Cell

III. EUKARYOTIC CELL STRUCTURES, cont

• Control center of eukaryotic cell

Double membrane that protects nucleus; continuous with ER

Contains pores

Site of ribosome production

DNA wrapped in protein

III. EUKARYOTIC CELL STRUCTURES, cont

• Suspended in cytosol or found on rough ER Site of protein production in a cell

III. EUKARYOTIC CELL STRUCTURES, cont

• Endomembrane System Endoplasmic Reticulum

Interconnected network continuous with nuclear envelope

Rough ER

Smooth ER

III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont

“Cell postmaster” Receives transport vesicles from ER; modifies, stores, and ships

products Receiving side is known as the cis face; shipping side is known as the trans face

III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont

Sacs containing hydrolytic enzymes Used for recycling cellular materials, destroying pathogens

III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont

Storage sac Plants typically have large,

central vacuole surrounded by membrane called tonoplast. Absorbs water and helps plant cell to grow larger

Some protists have contractile vacuole to pump out excess water

III. EUKARYOTIC CELL STRUCTURES, cont

• Site of oxidative respiration Contain own DNA, ribosomes Found in virtually all euk cells Enclosed by 2 membranes; inner membrane has folds called cristae

to increase surface area

III. EUKARYOTIC CELL STRUCTURES, cont

• Type of plastid that carries out photosynthesis by converting solar energy

to chemical energy (glucose) Contain membranous system of flattened sacs called thylakoids – stack is

called a granum Fluid surrounding thylakoids is called stroma Contains DNA, ribosomes

III. EUKARYOTIC CELL STRUCTURES, contEndosymbiont Theory

III. EUKARYOTIC CELL STRUCTURES, cont

• Membrane-bound compartments that use O2 to carry out metabolism H2O2 is produced; broken down by _________________

III. EUKARYOTIC CELL STRUCTURES, cont

• Provides structural support to cell Allows for movement Attachment site for organelles, enzymes More extensive in animal cells Composed of three types of proteins

Actin

More fixedKeratin

III. EUKARYOTIC CELL STRUCTURES, contCytoskeleton, cont

IV. CELL BOUNDARIES• Cell Wall

Found in

Rigid structure; protects, maintains shape of cells

Prevents excess water uptake Plant cell wall

CellulosePectin - Sticky polysaccharide

found between cell walls of adjacent cells

Plasmodesmata - Perforations between adjacent cell walls that allow for movement of materials from one cell to another

IV. CELL BOUNDARIES, cont• Extracellular Matrix of Animal Cells

Holds cells together, protects & supports cells Allows for communication between cells Composed primarily of glycoproteins – proteins with covalently-bonded

carbohydrate chains attached Must abundant glycoprotein in most animals is collagen

IV. CELL BOUNDARIES, cont• Intracellular Junctions

in Animal Cells Tight Junctions – Press

membranes together very tightly; prevents leakage of fluid

Desmosomes (Anchoring Junctions) – Fasten cells together in sheets

Gap Junctions – Allow for movement of cytoplasm from one cell to another; important in communication between cells

IV. CELL BOUNDARIES, cont• Cell (Plasma) Membrane

Selectively-permeable barrier found in all cells Composed primarily of phospholipid bilayer Fluid Mosaic Model

“Fluid” – Not a rigid structure. Organization due to high concentration of water inside & outside cell

IV. CELL BOUNDARIES, cont• Organization of Plasma Membrane

IV. CELL BOUNDARIES, cont

• Fluidity of Plasma Membrane

IV. CELL BOUNDARIES, cont• Cell Membrane, cont

Proteins - “Mosaic” – Assortment of different proteins embedded in bilayer; determine most of membrane’s specific functions. Act as channels, pumps, enzymes in metabolism, binding sites, etc

o Integral Proteins – Embedded in phospholipid layero Peripheral Proteins – Bound to surface of membrane

IV. CELL BOUNDARIES, contMembrane Proteins

IV. CELL BOUNDARIES, cont

• Cell Membrane, cont Carbohydrates

“ID tags” that identify cell.

Enable cells to recognize each other and foreign cells.

May be bonded to lipids (glycolipids) or proteins (glycoproteins)

IV. CELL BOUNDARIES, cont

V. CELL TRANSPORT

V. CELL TRANSPORT, cont• Passive Transport – Movement of materials from high to low

concentration. No energy output required. Diffusion

Random movement of a substance across membrane down concentration gradient

No net movement once equilibrium is reached

V. CELL TRANSPORT, cont• Passive Transport, cont

Facilitated Diffusion Passive transport of molecules across cell membrane with the help of

transport proteins Utilized by large molecules, charged particles, polar molecules Water

V. CELL TRANSPORT, cont• Passive Transport, cont

Osmosis – Diffusion of water across a membrane. Tonicity refers to tendency of cell to gain or lose water. If the solution is Isotonic relative to the cell – Solute concentration is same on both sides of

membrane. No net movement of water. Hypertonic relative to the cell – Concentration of solute is greater outside

cell → water moves out of cell until equilibrium is reached. Cell may shrivel. Hypotonic relative to the cell – Concentration of solute is lower outside cell

→ water moves into cell until equilibrium is reached. Cell may swell to bursting point.

V. CELL TRANSPORT, cont• Passive Transport / Osmosis, cont

Water Potential Used to predict the passive movement of water Designated as Ψ Water always moves from an area of higher water potential →

lower water potential

ΨS =

ΨP =

V. CELL TRANSPORT, cont• Passive Transport/Osmosis, cont

Osmoregulation Cells must have mechanism to prevent excess loss, uptake of waterCell wall, contractile vacuolePlasmolysis – Seen in plants; excessive water loss causes cell

membrane to pull away from cell wall

V. CELL TRANSPORT, cont

V. CELL TRANSPORT, cont• Active Transport

• Movement of materials against concentration gradient. Requires energy output by cell Carrier Proteins – Na+ / K+ Pump

V. CELL TRANSPORT, cont• Active Transport, cont

Proton Pump

V. CELL TRANSPORT, cont

• Active Transport, cont Exocytosis

Secretion of biomolecules by fusion of vesicles with cell membrane. Biomolecules “spit out”.

Hormones, neurotransmitters, etc

V. CELL TRANSPORT, cont• Active Transport, cont

Endocytosis – “Sucking In”. Cell membrane surrounds, engulfs particle or biomolecule, pinches in to form vesicle.Phagocytosis – “Sucking in” food particlesPinocytosis – “Sucking in” fluid dropletsReceptor-mediated Endocytosis – Very specific

VI. CELL SIGNALING

• Autocrine Signaling

VI. CELL SIGNALING, cont• Coordinates cell activities, development• Typically involves 3 steps:

Reception – Target cell’s detection of signal molecule due to binding of signal molecule to receptor protein in cell membrane

Transduction – Binding of signaling molecule changes receptor protein; triggers a sequence of events within cell

Response – Results in specific cellular response; for example, activation of genes, enzyme catalysis, etc.

VI. CELL SIGNALING, cont

• Reception Typically involves G Proteins

VI. CELL SIGNALING, cont• Transduction

Typically multi-step pathway Relay molecules are usually protein kinases

VI. CELL SIGNALING, cont

• Transduction Non-protein

molecule known as cAMP is often second messenger

VI. CELL SIGNALING, cont• Response

Nuclear May “turn on” or “turn off” genes

CytoplasmicMay regulate enzyme activity

ApoptosisControlled cell suicide

VI. CELL SIGNALING, cont

• Regulation