Cell Structure and FunctionChapter 6 and 7AP Biology

Cell

• Cells are the basic unit of structural and functional unit of living things.

• English scientist named Robert Hooke made a simple microscope. He observed small, box-shaped structures, called cellulae (meaning small room)

Cell Theory

• All living things are made of one or more cells.

• Cells are the basic unit of structure and function in the organization of 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.

Basic Structure of every Organism• Based on 1 of 2 types of cells• Prokaryotic• ‘pro’ =before• ‘karyon’ = kernel

• Eukaryotic• ‘eu’ = true• ‘karyon’ = kernel

Basic Structure of every Organism• Based on 1 of 2 types of cells• Prokaryotic• Only exist in domains of Bacteria or Archaea

• Eukaryotic• Protists, fungi, animals, and plants

Eukaryotic Cell (plant)

Eukaryotic Cell (animal)

Prokaryotic Cell (Bacteria)

Basic Common Feature of Both• Bound by selective barrier (plasma membrane)• Have cytosol (jellylike substance)• Where organelles and other components are found

• Contain chromosomes• Carry genes in the form of DNA

• Have ribosomes

Different Features of Both• Location of DNA• Eukaryotes• Most DNA is in nucleus• Nucleus is bound by double membrane• “true kernel”

• Prokaryotes• DNA is concentrated in region not membrane-enclosed• Nucleoid

Different Features of Both• Cytoplasm• Eukaryotes• Region between the nucleus and plasma membrane• Contains a variety of organelles of specialized form and

function• Prokaryotes• Interior of prokaryotic cell

Different Features of Both• Organelles• Eukaryotes• Membrane- bound organelles are Present• Specialized form and function

• Prokaryotes• Absence of organelles

Different Features of Both• Size• Eukaryotes• Generally Larger than prokaryotes• Size relates to function• 10 – 100um in diameter• Metabolic requirements limit size practicality of cells

• Prokaryotes• Smallest cells known• 1 – 5 um in diameter

Plasma Membrane• Acts as a selective barrier• Allows sufficient passage of oxygen, nutrients,

and wastes to service entire cell

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.

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)

Nucleus: Information Central

• Nucleus- contains cellular DNA which includes most of the genes in the cell. The nucleus is surrounded by the 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.

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.

Passive Transport• Passive Transport- moves solute from high to

low concentration. DO NOT requires energy.

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.

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