Chapter 3

Biology 25: Human Biology

Prof. Gonsalves

Los Angeles City College

Loosely Based on Mader’s Human Biology,7th edition

Cell Theory:Cell Theory: Developed in late 1800s. Developed in late 1800s.

1. All living organisms are made up of 1. All living organisms are made up of one or more cells.one or more cells.

2. The smallest living organisms are 2. The smallest living organisms are single cells, and cells are the functional single cells, and cells are the functional units of multicellular organisms.units of multicellular organisms.

3. All cells arise from preexisting cells.3. All cells arise from preexisting cells.

Microscope FeaturesMagnification:– Increase in apparent size of an object. – Ratio of image size to specimen size.

Resolving power: Measures clarity of image.– Ability to see fine detail.– Ability to distinguish two objects as separate.– Minimum distance between 2 points at which

they can be distinguished as separate and distinct.

Microscopes

Light Microscopes: Earliest microscopes used.

Lenses pass visible light through a specimen.

– Magnification: Highest possible from 1000 X to

2000 X.

– Resolving power: Up to 0.2 m (1 m = 1/1000

mm).

Types of Microscope

Electron Microscopes: Developed in 1950s. Electron

beam passes through specimen.– Magnification: Up to 200,000 X.– Resolving power: Up to 0.2 nm (1nm =

1/1’000,000 mm).

Two types of electron microscopes:

1. Scanning Electron Microscope: Used to study cell or virus surfaces.

2. Transmission Electron Microscope: Used to study internal cell structures.

Components of All Cells:

1. Plasma membrane: Separates cell contents from outside environment. Made up of phospholipid bilayers and proteins.

2. Cytoplasm: Liquid, jelly-like material inside cell.

3. Ribosomes: Necessary for protein synthesis.

Prokaryotic versus Eukaryotic CellsFeature Prokaryotic Eukaryotic

Organisms Bacteria All others (animals, plants,fungi, and protozoa)

Nucleus Absent Present

DNA One chromosome Multiple chromosomes

Size Small (1-10 um) Large (10 or more um)

Membrane Absent Present (mitochondria,Bound golgi, chloroplasts, etc.)Organelles

Division Rapid process Complex process(Binary fission) (Mitosis)

Eukaryotic Cells

– Include protist, fungi, plant, and animal cells.

– Nucleus: Protects and houses DNA

– Membrane-bound Organelles: Internal structures

with specific functions.• Separate and store compounds• Store energy• Work surfaces• Maintain concentration gradients

Functions of Cell Membranes 1. Separate cell from nonliving environment. Form

most organelles and partition cell into discrete compartments.

2. Regulate passage of materials in and out of the cell and organelles. Membrane is selectively permeable.

3. Receive information that permits cell to sense and respond to environmental changes.

• Hormones• Growth factors• Neurotransmitters

4. Communication with other cells and the organism as a whole. Surface proteins allow cells to recognize each other, adhere, and exchange materials.

I. Fluid Mosaic Model of the Membrane

1. Phospholipid bilayer: Major component is a phospholipid bilayer.• Hydrophobic tails face inward

• Hydrophilic heads face water

2. Mosaic of proteins: Proteins “float” in the phospholipid bilayer.

3. Cholesterol: Maintains proper membrane fluidity.

The outer and inner membrane surfaces are different.

A. Fluid Quality of Plasma Membranes

– In a living cell, membrane has same fluidity as salad oil.

• Unsaturated hydrocarbon tails INCREASE membrane fluidity

– Phospholipids and proteins drift laterally.• Phospholipids move very rapidly

• Proteins drift in membrane more slowly

– Cholesterol: Alters fluidity of the membrane• Decreases fluidity at warmer temperatures (> 37oC)

• Increases fluidity at lower temperatures (< 37oC)

B. Membranes Contain Two Types of Proteins

1. Integral membrane proteins:

Inserted into the membrane.

Hydrophobic region is adjacent to hydrocarbon tails.

2. Peripheral membrane proteins:

Attached to either the inner or outer membrane surface.

Functions of Membrane Proteins:

1. Transport of materials across membrane

2. Enzymes

3. Receptors of chemical messengers

4. Identification: Cell-cell recognition

5. Attachment:• Membrane to cytoskeleton• Intercellular junctions

C. Membrane Carbohydrates and Cell-Cell Recognition

– Found on outside surface of membrane.

– Important for Cell-cell recognition: Ability of one cell

to “recognize” other cells.

• Allows immune system to recognize self/non-self

• Include: – Glycolipids: Lipids with sugars

– Glycoproteins: Proteins with sugars

– Major histocompatibility proteins (MHC or transplantation antigens).

• Vary greatly among individuals and species.

• Organ transplants require matching of cell markers and/or immune suppression.

The cell plasma membrane is Selectively PermeableA. Permeability of the Lipid Bilayer

1. Non-polar (Hydrophobic) Molecules– Dissolve into the membrane and cross with ease– The smaller the molecule, the easier it can cross– Examples: O2 , hydrocarbons, steroids

2. Polar (Hydrophilic) Molecules

– Small polar uncharged molecules can pass through easily (e.g.: H2O , CO2)

– Large polar uncharged molecules pass with difficulty (e.g.: glucose)

3. Ionic (Hydrophilic) Molecules– Charged ions or particles cannot get through

(e.g.: ions such as Na+ , K+ , Cl- )

Transport Proteins in the membrane: Integral membrane proteins that allow for the transport of specific molecules across the phospholipid bilayer of the plasma membrane.How do they work?

• May provide a “hydrophilic tunnel” (channel)• May bind to molecule and physically move it• Are specific for the atom/molecule transported

III. Passive transport: Diffusion of molecules across the plasma membrane

A. Diffusion: The net movement of a substance from an area of high concentration to area of low concentration.

Does not require energy.

B. Passive transport: The diffusion of substance across a biological membrane.• Only substances which can cross bilayer

by themselves or with the aid of a protein

• Does not require the cell’s energy

Passive Transport: Diffusion Across a Membrane Does Not Require Energy

IV. Osmosis:

The diffusion of water across a semi-permeable

membrane.

Through osmosis water will move from an area

with higher water concentration to an area

with lower water concentration.

Solutes can’t move across the semi-permeable

membrane.

Osmotic Pressure: Ability of a solution to take up water through osmosis.

Example: The cytoplasm of a cell has a certain osmotic

pressure caused by the solutes it contains.There are three different types of solution when compared

to the interior (cytoplasm) of a cell:

1. Hypertonic solution: Higher osmotic pressure than cell due to:

Higher solute concentration than cell or

Lower water concentration than cell.

2. Hypotonic solution: Lower osmotic pressure than cell due to:

Lower solute concentration than cell or

Higher water concentration than cell.

3. Isotonic solution: Same osmotic pressure than cell.

Equal concentration of solute(s) and water than cell.

V. Cells depend on proper water balance

Animal Cells:

Do best in isotonic solutions.

Examples:• 0.9% NaCl (Saline)

• 5% Glucose

If solution is not isotonic, cell will be affected:

– Hypertonic solution: Cell undergoes crenation. Cell “shrivels” or shrinks.• Example: 5% NaCl or 10% glucose

– Hypotonic solution: Cell undegoes lysis. Cell swells and eventually bursts.• Example: Pure water.

VI. Facilitated Diffusion:

Some substances cannot cross the membrane by themselves due to their size or charge.

Membrane proteins facilitate the transport of solutes down their concentration gradient.

No cell energy is required.

Transport Proteins– Specific : Only transport very specific

molecules (binding site)• Glucose• Specific ions (Na+, K+, Cl- )

VII. Active Transport:

• Proteins use energy from ATP to actively “pump” solutes across the membrane

• Solutes are moved against a concentration gradient.

• Energy is required.

Example:

The Na+-K+ ATPase pump:

Energy of ATP hydrolysis is used to move Na+ out of the cell and K+ into the cell

Endocytosis: Moving materials into cell with vesicles.Requires use of cell energy.1. Pinocytosis (“Cell drinking”): Small droplets of liquid are taken into the cell through

tiny vesicles.

Not a specific process, all solutes in droplets are taken in.

2. Phagocytosis (“Cell eating”): Large solid particles are taken in by cell.

Example: Amoebas take in food particles by surrounding them with cytoplasmic

extensions called pseudopods.

Particles are surrounded by a vacuole.

Vacuole later fuses with the lysosome and contents are digested.

Endocytosis Uses Vesicles to Move Substances into the Cell

Endocytosis: 3. Receptor mediated endocytosis: Highly specific. Materials moved

into cell must bind to specific receptors first.Example: Low density lipoproteins (LDL):

– Main form of cholesterol in blood. – Globule of cholesterol surrounded by single layer of

phospholipids with embedded proteins. – Liver cell receptors bind to LDL proteins and remove LDLs

from blood through receptor mediated endocytosis.– Familial hypercholesterolemia: Genetic disorder in which

gene for the LDL receptor is mutated. Disorder found in 1 in 500 human babies worldwide. Results in unusually high levels of blood cholesterol.

Blood Cholesterol is Taken Up by Liver Cells through Receptor Mediated Endocytosis

Exocytosis:

Used to export materials out of cell.

Materials in vesicles fuse with cell membrane and are released to outside.

• Tear glands export salty solution.• Pancreas uses exocytosis to secrete

insulin.

Membrane-Bound Organelles of Eukaryotic Cells

• Nucleus

• Rough Endoplasmic Reticulum (RER)

• Smooth Endoplasmic Reticulum (SER)

• Golgi Apparatus

• Lysosomes

• Vacuoles

• Chloroplasts

• Mitochondria

Nucleus

Structure

• Double nuclear membrane (envelope)

• Large nuclear pores

• DNA (genetic material) is combined with histones and exists in two forms:

– Chromatin (Loose, threadlike DNA, most of cell life)

– Chromosomes (Tightly packaged DNA. Found only during cell division)

• Nucleolus: Dense region where ribosomes are made

Functions

• House and protect cell’s genetic information (DNA)

• Ribosome synthesis

Structure of Cell Nucleus

Endoplasmic Reticulum (ER)

– “Network within the cell”

– Extensive maze of membranes that branches throughout cytoplasm.

– ER is continuous with plasma membrane and outer nucleus membrane.

– Two types of ER:

• Rough Endoplasmic Reticulum (RER)

• Smooth Endoplasmic Reticulum (SER)

Rough Endoplasmic Reticulum (RER)

– Flat, interconnected, rough membrane sacs– “Rough”: Outer walls are covered with ribosomes.

– Ribosomes: Protein making “machines”. May exist free in cytoplasm or attached to ER.

– RER Functions:• Synthesis of cell and organelle membranes.• Synthesis and modification of proteins.• Packaging, and transport of proteins that are secreted from

the cell. – Example: Antibodies

Rough Endoplasmic Reticulum (RER)

Smooth Endoplasmic Reticulum (SER)

– Network of interconnected tubular smooth membranes.

– “Smooth”: No ribosomes

– SER Functions:• Synthesis of phospholipids, fatty acids, and steroids (sex

hormones).• Breakdown of toxic compounds (drugs, alcohol,

amphetamines, sedatives, antibiotics, etc.).• Helps develop tolerance to drugs and alcohol.• Regulates levels of sugar released from liver into the blood• Calcium storage for cell and muscle contraction.

Smooth Endoplasmic Reticulum (SER)

Golgi Apparatus

– Stacks of flattened membrane sacs that may be distended in certain regions. Sacs are not interconnected.

– First described in 1898 by Camillo Golgi (Italy).– Works closely with the ER to secrete proteins.

– Golgi Functions:• Receiving side receives proteins in transport vesicles

from ER.• Modifies proteins into final shape, sorts, and labels

proteins for proper transport.• Shipping side packages and sends proteins to cell

membrane for export or to other parts of the cell.• Packages digestive enzymes in lysosomes.

The Golgi Apparatus: Receiving, Processing, and Shipping of Proteins

Lysosomes– Small vesicles released from Golgi containing at

least 40 different digestive enzymes, which can break down carbohydrates, proteins, lipids, and nucleic acids.

– Optimal pH for enzymes is about 5– Found mainly in animal cells.– Lysosome Functions:

• Molecular garbage dump and recycler of macromolecules (e.g.: proteins).

• Destruction of foreign material, bacteria, viruses, and old or damaged cell components.

• Digestion of food particles taken in by cell.

• After cell dies, lysosomal membrane breaks down, causing rapid self-destruction.

Lysosomes: Intracellular Digestion

Lysosomes, Aging, and Disease

– As we get older, our lysosomes become leaky, releasing enzymes which cause tissue damage and inflammation.

• Example: Cartilage damage in arthritis.

– Steroids or cortisone-like anti-inflammatory agents stabilize lysosomal membranes, but have other undesirable effects (affect immune function).

– Diseases from “mutant” lysosome enzymes are usually fatal:

• Pompe’s disease: Defective glycogen breakdown in liver.

• Tay-Sachs disease: Defective lipid breakdown in brain. Common genetic disorder among Jewish people.

Mitochondria (Sing. Mitochondrion)

– Site of cellular respiration:

Food (sugar) + O2 -----> CO2 + H2O + ATP

– Change chemical energy of molecules into the useable energy of the ATP molecule.

– Oval or sausage shaped.– Contain their own DNA, ribosomes, and make some proteins. – Can divide to form daughter mitochondria.– Structure:

• Inner and outer membranes.

• Intermembrane space

• Cristae (inner membrane extensions)

• Matrix (inner liquid)

Mitochondria Harvest Chemical Energy From Food

The Cytoskeleton

Complex network of thread-like and tube-like structures.Functions: Movement, structure, and structural support.

Three Cytoskeleton Components:

1. Microfilaments: Smallest cytoskeleton fibers.

Important for:

• Muscle contraction: Actin & myosin fibers in muscle

cells

• “Amoeboid motion” of white blood cells

Components of the Cytoskeleton are Important for Structure and Movement

Three Cytoskeleton Components:

2. Intermediate filaments: Medium sized fibers• Anchor organelles (nucleus) and hold cytoskeleton in place.• Abundant in cells with high mechanical stress.

3. Microtubules: Largest cytoskeleton fibers. Found in:• Centrioles: A pair of structures that help move

chromosomes during cell division (mitosis and meiosis). Found in animal cells, but not plant cells.• Movement of flagella and cilia.

Cilia and Flagella– Projections used for locomotion or to move

substances along cell surface. – Enclosed by plasma membrane and contain

cytoplasm.– Consist of 9 pairs of microtubules surrounding

two single microtubules (9 + 2 arrangement).Flagella: Large whip-like projections. Move in wavelike manner, used for locomotion.

• Example: Sperm cell

Cilia: Short hair-like projections.• Example: Human respiratory system uses cilia to

remove harmful objects from bronchial tubes and trachea.

Structure of eukaryotic Flagellum

Summary of Eukaryotic Organelles Function: Manufacture

– Nucleus– Ribosomes– Rough ER– Smooth ER– Golgi Apparatus

Function: Breakdown– Lysosomes– Vacuoles

Summary of Eukaryotic Organelles Function: Energy Processing

– Chloroplasts (Plants and algae)– Mitochondria

Function: Support, Movement, Communication– Cytoskeleton (Cilia, flagella, and centrioles)– Cell walls (Plants, fungi, bacteria, and some

protists)– Extracellular matrix (Animals)– Cell junctions

Metabolism: All chemical processes that occur within a living organism. Either catabolic or anabolic reactions.

I. Catabolic Reactions:

– Release energy (exergonic).

– Break down large molecules (proteins, polysaccharides) into their building blocks (amino acids, simple sugars).

– Often coupled to the endergonic synthesis of ATP.Examples:

1. Cellular respiration is a catabolic process:

C6H12O6 + 6 O2 -------> 6 CO2 + 6 H2O + EnergySugar Oxygen Carbon dioxide Water

2. The digestion of sucrose is a catabolic process:

Sucrose + Water -------> Glucose + Fructose + EnergyDisaccharide Monosaccharides

Metabolism: Catabolism + Anabolism II. Anabolic Reactions:

– Require energy (endergonic).

– Build large molecules (proteins, polysaccharides) from their building blocks (amino acids, simple sugars).

– Often coupled to the exergonic breakdown or hydrolysis of ATP.Examples:

1. Photosynthesis is an anabolic process:

6 CO2 + 6 H2O + Sunlight ----> C6H12O6 + 6 O2

Carbon Water Sugar Oxygen

Dioxide

2. Synthesis of sucrose is an anabolic process:

Glucose + Fructose + Energy -------> Sucrose + H2OMonosaccharides Disaccharide

V. ATP: Shuttles Chemical Energy in the Cell

– Coupled Reactions: • Endergonic and exergonic reactions are often coupled to

each other in living organisms.

• The energy released by exergonic reactions is used to fuel endergonic reactions.

– ATP “shuttles” energy around the cell from exergonic reactions to endergonic reactions.

• One cell makes and hydrolyzes about 10 million ATPs/second.

• Cells contain a small supply of ATP molecules (1-5 seconds).

– ATP powers nearly all forms of cellular work:1. Mechanical work: Muscle contraction, beating of flagella

and cilia, cell movement, movement of organelles, cell division.

2. Transport work: Moving things in & out of cells.3. Chemical work: All endergonic reactions.

A. Structure of ATP (Adenosine triphosphate)

• Adenine: Nitrogenous base.

• Ribose: Pentose sugar, same ribose of RNA.

• Three Phosphate groups: High energy bonds.

B. ATP Releases Energy When Phosphates Are

Removed:

Phosphate bonds are rich in chemical energy and easily broken by hydrolysis:ATP + H2O ----> ADP + Energy + Pi

ADP + H2O ----> AMP + Energy + Pi

VI. Enzymes: • Protein molecules that catalyze the reactions of living

organisms.

• Enzymes increase the rate of a chemical reaction without being consumed in the process.

• Name: Substrate (or activity) + ase suffix

Examples:

– Sucrase

– Lipase

– Proteinase

– Dehydrogenase (Removes H atoms)

• Enzymes are specific: Catalyze one or a few related reactions.

• Enzymes are efficient. Can increase the rate of a reaction 10 to billions of times!!!!

VI. Enzymes: – Enzymes increase the rate of a chemical

reaction by lowering the activation energy required to initiate the reaction.

– Activation energy of a reaction: Energetic barrier that reactant molecules must overcome for reaction to proceed.

Creation of new bonds requires breaking of old bonds.

• Both exergonic and endergonic reactions

• Transition state :“Intermediate” state of

reactants

Enzyme Mechanism of Action: 1. Binding: Enzyme binds to the reactant(s), forming an

enzyme-substrate complex.

• Substrate: The reactant the enzyme acts upon to

lower the activation energy of the reaction.

• Active site: Region on enzyme where binding to

substrate occurs.

– Active site dependent upon proper 3-D conformation.

Enzyme Mechanism of Action:

2. Induced fit model: After enzyme binds to substrate, it

changes shape and lowers activation energy of the reaction

by one of several mechanisms:

• Straining chemical bonds of the substrate

• Bringing two or more reactants close together

• Providing “micro-environment” conducive to reaction3. Release: Once product is made, it is released from active site

of enzyme. Enzyme is ready to bind to another substrate molecule.

CELLULAR RESPIRATION BANKS ATP

REACTION:C6H12O6 + 6O2 ----> 6CO2 + 6H2O + ENERGY(Glucose) (Oxygen) (Carbon dioxide) (Water)

What happens to the energy in glucose or other food molecules?

– Only about 40% of energy is turned into ATP

– The rest is lost as metabolic heat.– One ATP molecule has about 1% of the

chemical energy found in glucose.

MAJOR CATABOLIC PATHWAYSA. Aerobic (Cellular) respiration:

– Requires oxygen.– Most commonly used catabolic pathway.– Over 30 reactions. Used to extract

energy from glucose molecules.– Final electron acceptor: Oxygen.– Most efficient: 40% of glucose energy is

converted into ATP.REACTION:

C6H12O6 + 6O2 ---> 6CO2 + 6H2O + ENERGYGlucose Oxygen Carbon dioxide Water

V. Three Stages of Cellular Respiration

A. Glycolysis

B. Kreb’s Cycle

C. Electron Transport Chain & Chemiosmosis

A. Glycolysis: “Splitting sugar” – Occurs in the cytoplasm of the cell– Does not require oxygen– 9 chemical reactions– Net result: Glucose molecule (6 carbons each) is split into

two pyruvic acid molecules of 3 carbons each.– Yield per glucose molecule:

2 ATP ( Substrate-level phosphorylation)2 NADH + 2 H+ (2 ATP are “invested” to get 4 ATP back)

– Pyruvic acid diffuses into mitochondrial matrix where all subsequent reactions take place.

Conversion of Pyruvate to Acetyl CoA

– Before entering the next stage, pyruvic acid (3C) must be converted to Acetyl CoA (2 C).

– A carbon atom is lost as CO2.

– Yield per glucose molecule: 2 NADH + 2 H+

B. Kreb’s Cycle

– Occurs in the matrix of the mitochondrion– A cycle of 8 reactions

• Reaction 1: Acetyl CoA (2C) joins with 4C molecule (oxaloacetic acid) to produce citric acid (6C).

• Reactions 2 & 3: Citric acid loses 2C atoms as CO2.• Reactions 4 & 5: REDOX reactions produce NADH and

FADH2.• Reactions 6-8: Oxaloacetic acid is regenerated.

B. Kreb’s Cycle

– Carbons are released as CO2

– Yield per glucose molecule:

2 ATP (substrate-level phosphorylation)

6 NADH + 6 H+

2 FADH2

C. Electron Transport Chain & Chemiosmosis

– Most ATP is produced at this stage– Occurs on inner mitochondrial membrane– Electrons from NADH and FADH2 are transferred to

electron acceptors, which produces a proton gradient– Proton gradient used to drive synthesis of ATP.– Chemiosmosis: ATP synthase allows H+ to flow across

inner mitochondrial membrane down concentration gradient, which produces ATP.

– Ultimate acceptor of H+ and electrons is OXYGEN, producing water.

C. Electron Transport Chain & Chemiosmosis

Yield of ATP through Chemiosmosis:– Each NADH produces 3 ATP

– Each FAHD2 produces 2 ATP

2 NADH (Glycolysis) x 3 ATP = 6 ATP

2 NADH (Acetyl CoA) x 3 ATP = 6 ATP

6 NADH (Kreb’s cycle) x 3 ATP = 18 ATP

2 FADH2 (Kreb’s cycle) x 2 ATP = 4 ATP

________________

32 - 34 ATP

These ATPs are made by oxidative phosphorylation

or chemiosmosis.

VIII. Total Energy from cellular respirationSubstrate Oxidative

Process Phosphoryl e-Carrier PhosphorylTOTAL

Glycolysis 2 ATP 2 NADH ---> 4 - 6 ATP 6-8 ATP

Acetyl CoA 2 NADH ---> 6 ATP 6 ATP

Formation

Kreb’s 2 ATP 6 NADH --->18 ATP

2 FADH2 ---> 6 ATP 24 ATP

__________

Total yield per glucose : 36-38 ATP

THREE MAJOR CATABOLIC PATHWAYS

B. Anaerobic respiration:

– Does not require oxygen.

– Used by bacteria that live in environments without oxygen.

– Final electron acceptor: Inorganic molecule.

– Very inefficient: Only 2% of glucose energy is converted into ATP.

– Final products: Carbon dioxide, water, and other inorganic compounds.

THREE MAJOR CATABOLIC PATHWAYS

C. Fermentation: – Does not require oxygen.– Used by yeast, bacteria, and other cells when

oxygen is not available.– Final electron acceptor: Organic molecule.– Very inefficient: Only 2% of glucose energy is

converted into ATP.– Products depend on type of fermentation:

• Lactic acid fermentation: Used to make cheese and yogurt. Carried out by muscle cells if oxygen is low.

• Alcoholic fermentation: Used to make alcoholic beverages. Produces alcohol and carbon dioxide.