AP chpt 3

Cell theory

• All organisms are made of one or more cells

• The cell is the smallest unit of life

• All cells arise from preexisting cells

Principle of complementarity & compartmentalization

• Specific cell structures and organelles determine what functions a cell can perform
• Eukaryotic cells are divided into specialized compartments
• This allows different functions to occur efficiently

Basic components of a cell

• Plasma membrane
• Cytoplasm
• Nucleus
• Cytoplasm includes:
◦ Cytosol
◦ Organelles
◦ Inclusions

Cytosol vs. extracellular fluid (ECF)

• Cytosol: viscous intracellular fluid inside the cell
• Extracellular fluid (ECF): fluid outside the cell

Organelles vs. inclusions

• Organelles:
◦ Internal structures that perform specialized metabolic tasks
• Inclusions:
◦ Stored substances in the cytoplasm
◦ Examples: nutrients, lipids, pigments, and crystals

Membranous vs. nonmembranous organelles

• Nonmembranous:
◦ Ribosomes
◦ Centrosomes
◦ Centrioles
◦ Basal bodies
• Membranous:
◦ Nucleus
◦ Endoplasmic reticulum
◦ Golgi body
◦ Lysosomes
◦ Peroxisomes
◦ Mitochondria

Selective permeability

• Ability of the plasma membrane to:
◦ Allow some substances to cross
◦ Block other substances

Phospholipid bilayer

• Two layers of phospholipids
• Forms the basic structure of the plasma membrane
• Polar, hydrophilic heads face outward
• Nonpolar, hydrophobic tails face inward

Which molecules pass easily through the phospholipid bilayer, and why do polar molecules struggle?

• Easily pass:
◦ Nonpolar
◦ Hydrophobic
◦ Lipid-soluble molecules
• Polar molecules struggle because:
◦ The interior of the bilayer is hydrophobic

Fluid mosaic model

• The plasma membrane is fluid
• Made of a phospholipid bilayer with proteins floating within or on it
• Kinked phospholipid tails:
◦ Prevent phospholipids from packing tightly
◦ Help maintain membrane fluidity

Major components of the plasma membrane

• Phospholipids
• Cholesterol
• Glycolipids
• Proteins
• Glycoproteins

Six types of membrane proteins

• Transport proteins:
◦ Move substances
• Enzyme proteins:
◦ Carry out reactions
• Receptor proteins:
◦ Bind chemical messengers
• Recognition proteins:
◦ Identify cells
• Intercellular joining proteins:
◦ Help cells adhere
• Attachment proteins:
◦ Connect the membrane to the cytoskeleton or extracellular matrix

Glycocalyx

• Fuzzy carbohydrate coat outside the plasma membrane
• Made of:
◦ Glycoproteins
◦ Glycolipids
• Functions:
◦ Protection
◦ Cell adhesion and recognition
◦ Immunity
◦ Fertilization
◦ Embryonic development
◦ Cancer defense
◦ Transplant compatibility

Microvilli & brush border

• Microvilli:
◦ Plasma membrane extensions
◦ Increase surface area
• Especially common in absorptive cells:
◦ Intestines
◦ Kidney tubules
• Dense microvilli create a:
◦ Brush border

Cytoskeleton

• Network of filaments and tubules
• Functions:
◦ Maintains cell shape
◦ Provides support
◦ Transports materials within the cell
◦ Allows movement of cells and organelles
• Three components:
◦ Microfilaments
◦ Intermediate filaments
◦ Microtubules

Microfilaments, intermediate filaments, and microtubules

• Microfilaments:
◦ Help change cell shape
• Intermediate filaments:
◦ Help maintain cell shape
• Microtubules:
◦ Help maintain cell shape
◦ Move organelles
◦ Allow movement through cilia and flagella

Cilia vs. flagella

• Cilia:
◦ Move air or fluid along a cell's surface
◦ Shorter
◦ More numerous
• Flagella:
◦ Provide cell motility
◦ Longer
◦ Fewer in number
◦ Example: sperm cells

Centrioles & centrosome

• Centrioles:
◦ Short microtubules
◦ Arranged in 9 groups of 3
◦ Help with cell division
• Centrosome:
◦ Small area of cytoplasm
◦ Contains two centrioles

Ribosomes

• Site of protein synthesis
• Made of:
◦ Large subunit
◦ Small subunit
◦ Proteins
◦ Ribosomal RNA (rRNA)
• Free ribosomes:
◦ Float in the cytosol
• Bound ribosomes:
◦ Attached to the rough ER

Nucleus

• Largest organelle
• Functions:
◦ Cell's control center
◦ Stores genetic information in DNA
• Three main structures:
◦ Nuclear envelope
◦ Nucleolus
◦ Chromatin

Nuclear envelope & nuclear pores

• Nuclear envelope:
◦ Double membrane surrounding the nucleus
◦ Outer membrane is continuous with the rough ER
• Nuclear pores:
◦ Control what enters and leaves the nucleus

What enters and leaves the nucleus?

• Enters:
◦ Raw materials for nucleotides
◦ Enzymes
◦ ATP
• Leaves:
◦ mRNA
◦ Waste
• DNA:
◦ Does not leave the nucleus

Nucleolus

• Site of:
◦ rRNA synthesis
◦ Production of new ribosomes

Chromatin

• DNA wrapped around histone proteins
• Forms threadlike material
• Can coil into chromosomes

Multinucleate vs. anucleate cells

• Multinucleate cells:
◦ Have more than one nucleus
◦ Example: skeletal muscle cells
• Anucleate cells:
◦ Lack a nucleus
◦ Example: mature red blood cells
◦ Cannot reproduce or make proteins

Endomembrane system

• Network of membranes including:
◦ Nuclear envelope
◦ Rough ER
◦ Smooth ER
◦ Golgi body
◦ Lysosomes
◦ Vesicles
• Materials move between compartments because membranes can:
◦ Bud off
◦ Merge with one another

Vesicles

• Tiny membrane-bound sacs
• Transport materials:
◦ Through the cytosol
◦ Between parts of the endomembrane system

Rough ER (RER)

• Has attached ribosomes
• Functions:
◦ Protein synthesis
◦ Protein processing
• Basic process:
◦ Protein chain enters the cisternal space
◦ Protein folds
◦ Side chains may be added
◦ Protein is packaged into a transport vesicle

Smooth ER (SER)

• Lacks ribosomes
• Does not synthesize proteins
• Functions:
◦ Lipid metabolism
◦ Cholesterol synthesis
◦ Steroid hormone synthesis
◦ Fat synthesis and transport
◦ Detoxification of drugs and carcinogens
◦ Absorption
◦ Storage

Golgi body

• Stack of membranous sacs
• Receives protein-filled vesicles from the ER
• Functions:
◦ Modifies
◦ Sorts
◦ Packages
◦ Ships contents

Lysosomes

• Contain digestive enzymes
• Break down:
◦ Large organic molecules
◦ Portions of cytosol
◦ Worn-out organelles
◦ Glycogen
◦ Whole cells
◦ Bone
• Interior is acidic:
◦ About pH 5
◦ Provides optimal conditions for digestive enzymes

Autophagy vs. autolysis

• Autophagy:
◦ Digestion and recycling of worn-out organelles
◦ Example: mitochondria
• Autolysis:
◦ Cell suicide
◦ Cell destroys itself after completing its function

Peroxisomes & catalase

• Peroxisomes:
◦ Break down fatty acids
◦ Break down amino acids
◦ Neutralize free radicals
◦ Produce hydrogen peroxide (H₂O₂)
• Catalase:
◦ Breaks H₂O₂ into water and oxygen

Mitochondria

• Perform cellular respiration
• Produce ATP using:
◦ Glucose
◦ Oxygen
• Cells with high energy demands have many mitochondria
• Example:
◦ Muscle cells

Why are mitochondria called the powerhouses of the cell?

• Produce ATP
• ATP provides energy for cellular processes

Mitochondrial structure

• Double membrane:
◦ Continuous outer membrane
◦ Highly folded inner membrane
• Cristae:
◦ Folds of the inner membrane
◦ Increase surface area for chemical reactions
• Matrix:
◦ Semifluid interior

Evidence for the endosymbiotic origin of mitochondria

• Can replicate themselves
• Contain their own:
◦ DNA
◦ Ribosomes
• These features are similar to prokaryotes

Passive vs. active vs. vesicular transport

• Passive transport:
◦ Does not require ATP
◦ Powered by random molecular motion
• Active transport:
◦ Uses ATP
◦ Moves substances against a gradient
• Vesicular transport:
◦ Uses membrane-bound vesicles
◦ Moves large particles, fluid droplets, or many molecules at once

Three types of passive transport

• Filtration
• Diffusion
• Osmosis

Carrier-mediated transport

• Uses membrane carrier proteins
• Moves substances across the membrane
• Two types:
◦ Facilitated diffusion
◦ Active transport

Filtration

• Movement of particles through a selectively permeable membrane
• Driven by hydrostatic pressure
• Hydrostatic pressure:
◦ Force exerted by water against the membrane

Simple diffusion

• Net movement of particles:
◦ High concentration → low concentration
• Occurs because of constant random motion
• Moves down a concentration gradient

Concentration gradient

• Difference in the concentration of a substance between two areas

Factors affecting the rate of diffusion

• Temperature:
◦ Higher temperature = faster diffusion
• Molecular weight:
◦ Larger molecules = slower diffusion
• Concentration gradient:
◦ Steeper gradient = faster diffusion
• Membrane surface area:
◦ Greater surface area = faster diffusion
• Membrane permeability:
◦ Greater permeability = faster diffusion

Diffusion through the membrane

• Through phospholipid bilayer:
◦ Nonpolar
◦ Hydrophobic
◦ Lipid-soluble substances
• Through channel proteins:
◦ Water
◦ Charged solutes
◦ Hydrophilic solutes
• Cells regulate permeability by:
◦ Changing the number of channels
◦ Opening or closing channel gates

Osmosis

• Movement of water across a selectively permeable membrane
• Moves:
◦ Higher water concentration → lower water concentration

Hydration spheres

• Water molecules surrounding solute particles
• These water molecules are less available to diffuse freely

Aquaporins

• Channel proteins specialized for water transport
• More aquaporins:
◦ Increase the rate of osmosis

Osmotic pressure

• Amount of hydrostatic pressure required to stop osmosis
• More solute:
◦ Higher osmotic pressure
• Reverse osmosis:
◦ Applied pressure overrides osmotic pressure
◦ Pushes water against its concentration gradient

Osmolarity vs. osmolality

• Osmolarity:
◦ Number of osmoles of solute per liter of solution
• Osmolality:
◦ Number of osmoles of solute per kilogram of water
• Higher solute concentration:
◦ Higher osmolarity
• Normal blood plasma:
◦ About 300 mOsm/L

Tonicity

• Ability of a solution to affect:
◦ Cell fluid volume
◦ Cell pressure

Hypotonic, hypertonic, and isotonic solutions

• Hypotonic:
◦ Lower concentration of nonpermeating solutes than the cell
◦ Water enters
◦ Cell swells and may lyse
• Hypertonic:
◦ Higher concentration of nonpermeating solutes than the cell
◦ Water leaves
◦ Cell shrivels or crenates
• Isotonic:
◦ No net change in cell volume or shape
◦ Example: normal saline

Carrier protein specificity & saturation

• Specificity:
◦ Carrier proteins usually transport certain molecules or ligands
• Saturation:
◦ Transport rate increases as solute concentration increases
◦ Eventually all carriers become occupied
• Transport maximum (Tm):
◦ Maximum transport rate when all carriers are occupied

Uniport vs. symport vs. antiport

• Uniport:
◦ Transports one solute
• Symport:
◦ Transports two or more solutes
◦ Same direction
• Antiport:
◦ Transports two or more solutes
◦ Opposite directions

Facilitated diffusion

• Carrier-mediated transport
• Moves solutes:
◦ Down their concentration gradient
◦ Without ATP
• Process:
◦ Solute binds to carrier
◦ Carrier changes shape
◦ Solute is released on the other side

Active transport

• Carrier-mediated transport
• Moves solutes:
◦ Against their concentration gradient
◦ Using ATP
• Examples:
◦ Sodium-potassium pump
◦ Amino acid transport into cells
◦ Calcium pumped out of cells

Sodium-potassium pump

• Active transport mechanism
• Uses:
◦ 1 ATP per cycle
• Moves:
◦ 3 Na⁺ out of the cell
◦ 2 K⁺ into the cell
• Maintains:
◦ High K⁺ inside the cell
◦ Low Na⁺ inside the cell
• Necessary because Na⁺ and K⁺ constantly leak across the membrane

Endocytosis vs. exocytosis

• Endocytosis:
◦ Brings material into the cell using vesicles
• Exocytosis:
◦ Releases or secretes material from the cell
◦ Replaces plasma membrane lost during endocytosis

Phagocytosis

• "Cell eating"
• Engulfs large particles
• Functions:
◦ Removes debris
◦ Removes infectious microorganisms

Pinocytosis

• "Cell drinking"
• Takes in droplets of extracellular fluid containing useful molecules
• Process:
◦ Plasma membrane caves inward
◦ Pinches off
◦ Forms a pinocytotic vesicle

Receptor-mediated endocytosis

• Selective form of endocytosis
• Specific extracellular molecules bind to membrane receptors
• Process:
◦ Clathrin-coated pit forms
◦ Pit pinches off
◦ Forms a clathrin-coated vesicle
◦ Vesicle contains concentrated molecules