Cell Structure and FunctionChapter 6 and 7AP Biology

Cell Theory• All living things are made of cells.• Cells are the basic unit of structure and

function in living things.• All cells come from pre-existing cells.

Eukaryotic vs. Prokaryotic Cells• Eukaryotic cells contain DNA in the

nucleus. Prokaryotic cells contain DNA in a concentrated region called the nucleoid.

The Plasma Membrane• Plasma

Membrane- a selective barrier (semipermeable) that allows passage of enough oxygen, nutrients, and wastes to and from the cell. • The plasma membrane is a lipid bilayer embedded with diverse proteins.

Surface Area to Volume Ratio• As you ___________ the cell size, you

____________ the surface area to volume ratio, which ___________ the efficiency of transport across the cell membrane.

Surface Area to Volume Ratio

Animal Cell

Plant Cell

Nucleus: Information Central• Nucleus- contains cellular

DNA which includes most of the genes in the cell. The nucleus is surrounded by the nuclear envelope.• The nuclear envelope is a double membrane made of 2 lipid bilayers. Includes pore structures that help regulate things entering and exiting the nucleus.• Nuclear Lamina- a net of protein filaments that maintain shape of nucleus and support nuclear envelope.

Nucleus: Information Central• Chromosomes- structures that carry genetic information (DNA). Each chromosome contains one long DNA molecule.• Each eukaryotic species has a

distinct number of chromosomes.

• Chromatin- the complex of DNA and protein making up chromosomes. •Nucleolus- helps synthesize rRNA (ribosomal RNA) and ribosomes.

Ribosomes: Protein Factory• Ribosomes- made of rRNA and proteins-

carry out protein synthesis. • Ribosomes exist as either free ribosomes (suspended in cytosol) or bound ribosomes (attached to the Rough ER or nuclear envelope)

Endoplasmic Reticulum: Biological Factory• Endoplasmic Reticulum- consists of

membranous tubules, and sacs, called cisternae.

• Smooth ER- lacks ribosomes. Functions lipid synthesis, detoxification, and storing calcium ions.

• Rough ER- has ribosomes on surface. Continuous with the nuclear envelope. Synthesizes glycoproteins and other secretory proteins.

Golgi Apparatus: Shipping and Receiving• Golgi Apparatus- made of flattened

membranous sacs called cisternae. Has 2 sides the cis face (receiving) and the trans face (shipping).

Lysosomes: Digestive Compartments• Lysosome- contains hydrolytic enzymes

used to digest molecules.• Phagocytosis- “cell eating”- lysosome digesting food• Autophagy- lysosome breaking down damaged organelles.

Vacuoles: Storage Centers• Vacuole- functions vary depending on cell

type.• Food Vacuole• Contractile Vacuole• Central Vacuole

Mitochondria: Chemical Energy Supercenter• Mitochondria- site of

cellular respiration. • Cellular Respiration- the process that uses O2 to generate ATP by extracting energy from sugars, fats, and other fuels.

Chloroplast: Light Energy Capturer • Chloroplast- found in plants and algae-

the site of photosynthesis. Contain the green pigment chlorophyll.• Is a member of the plastid family- a group of plant organelles.

Endosymbiont Theory

Peroxisomes: Oxidation• Peroxisomes- contain enzymes that

remove hydrogen atoms and transfer them to oxygen, producing hydrogen peroxide (H2O2).

Cytoskeleton• Cytoskeleton- a network of fibers

extending throughout the cytoplasm- plays a major role in organizing the structure and activities of the cells.•Motor Proteins- allows for cell movement.

Cytoskeleton• Microtubules- the thickest cytoskeletal

fiber, provide a track that organelles with motor proteins can move along. Help separate chromosomes during mitosis. Form flagella and cilia.• Centrosome- region where microtubules are organized. Contains a pair of centrioles. Only in animal cells.

Cytoskeleton• Microfilaments- the thinnest fiber. Actin

and myosin filaments help muscle cells contract. Aide in pseudopodia movement by converting cytoplasm from a liquid to a gel.• Cytoplasmic Streaming- circular flow of cytoplasm within cells. Speeds distribution of cell materials.

Cytoskeleton• Intermediate Filaments- more

permanent fixtures, fix the position of organelles and shape of the cell. Include keratin proteins.

Cell Wall• Cell Wall- extracellular structure of plant

cells. Protects the cell, maintains its shape, and prevents excessive uptake of water. Holds the plant up against gravity.• Primary Cell Wall, Middle Lamella, Secondary Cell

Wall• Plasmodesmata-perforations in the plant cell wall

that allows cytoplasm to be continuous between neighboring plant cells.

Extracellular Matrix• Extracellular Matrix (ECM)- glycoproteins,

carbohydrates and proteoglycans that form strong fibers outside of cells.

Warm Up Exercise• What are the three components of the

cytoskeleton?• Which cytoskeletal component provides

tracks for motor proteins to move along within the cell?

• Which cytoskeletal structure helps muscles contract?

• Which cytoskeletal component helps form cilia and flagella?

Fluid Mosaic Model• Fluid Mosaic Model- membrane is a fluid

structure with a “mosaic” of various proteins embedded in or attached to a phospholipid bilayer. (lipids and proteins are amphipathic)

Membrane Proteins• Integral Proteins- penetrate the hydrophobic

interior of he lipid bilayer. (Ex: integrins)• Most of these are transmembrane proteins which span the

entire membrane.• Peripheral Proteins- loosely bound to the

surface of the membrane. Not embedded at all.

Functions of Membrane Proteins• Transport• Enzymatic Activity• Signal Transduction• Cell to Cell Recognition• Intercellular Joining• Attachment to Cytoskeleton

and ECM

Membrane Fluidity• Membranes are held together by weak

hydrophobic interactions.

Membrane Fluidity• Membrane remains fluid as temperature

decreases, until phospholipids pack so closely together that the membrane solidifies.

• Cholesterol reduces membrane fluidity at high temperatures by reducing movement. It also prevents packing, slowing solidification at low temperatures.

Membrane Permeability• Transport Proteins• Channel Proteins- provide a channel for hydrophilic molecules to move through.• Aquaporins- allow water to pass through the

cell membrane quickly.• Carrier Proteins- bind to molecules and shuttle them across the membrane.

Diffusion• Diffusion- movement of molecules of any

substance until they spread out evenly in the available space. (equilibrium).• Diffusion is a spontaneous process, needing no

energy input.• Rule of Diffusion: in the absence of a force, a

substance will diffuse from high concentration to low concentration.

Diffusion• A substance diffuses down its own concentration

gradient, unaffected by the concentration of other substances.

• Diffusion is a form of passive transport- movement that does not require the cell to use energy.

Osmosis• Osmosis- the diffusion

of water. Water diffuses from the region of lower solute concentration (higher free water concentration) to the area of higher solute concentration (lower free water concentration)- until equilibrium is reached. • Osmosis is a method of

passive transport

Osmosis• Tonicity- the ability of a surrounding solution to

cause a cell to gain or lose water.• Hypertonic- concentration of solution is more than

the cell. Cell will lose water, shrivel, and probably die.• Hypotonic- concentration of solution is less than the

cell. Water will enter the cell and the cell will swell and lyse (burst). • Isotonic- concentration of solutions is the same on

both sides of the membrane. No net movement of water = stable volume.

Osmosis• Osmoregulation- the control of solute

concentrations and water balance. • Less permeable membrane, contractile vacuole, etc.

Facilitated Diffusion• Facilitated Diffusion- passive transport aided by

proteins. • Frequently involves polar molecules.

• Ion Channels- channel proteins that transport ions down the concentration gradient. No energy required.• Gated Channels- open or close in response to a

stimulus.

Active Transport• Active Transport- moves solute from low to high

concentration. Requires energy (usually ATP). Uses carrier proteins.• Active transport allows a cell to have an internal

concentration different from its surroundings.• Sodium-Potassium Pump- an example of active

transport that exchanges Na+ for K+ across the plasma membrane.

Active Transport• Membrane Potential – the difference in voltage

across the cell membrane. (ranges from -50 to -200 mV)• The inside of the cell is negative relative to the

outside.• This favors transport of cations into the cell and

anions out of the cell.• Electrochemical Gradient- the combination of

the membrane potential (electrical force) and concentration gradient (chemical force).• Ions diffuse not only down their concentration

gradient, but down its electrochemical gradient.

Active Transport• Electrogenic Pump- a transport protein that

generates voltages across a cell membrane by maintaining a membrane potential.• Ex. Sodium-potassium pump in animals and proton

pump in plants, fungi and bacteria

Cotransport• Cotransport- active transport driven by a

concentration gradient.

Endocytosis/Exocytosis• Exocytosis- the

secretion of large molecules by the fusion of vesicles with the plasma membrane. Requires energy.

• Endocytosis- cell takes in molecules by forming new vesicles from the plasma membrane.• Phagocytosis- cell eating• Pinocytosis- cell drinking• Receptor-Mediated

Endocytosis

Endocytosis/Exocytosis