Cell Structure and Function

Cells

• Smallest living unit• (plants and animals

are composed of cells)

• Most are microscopic

Discovery of Cells

• Robert Hooke (mid-1600s)– Observed sliver of cork– Saw “row of empty boxes”– Coined the term cell

Cell theory

• (1839)Theodor Schwann & Matthias Schleiden

“ all living things are made of cells”

• (50 yrs. Later) Louis Pasteur

“all cells come from cells”

Principles of Cell Theory

• All living things are made of cells• The smallest living unit of structure

and function of all organisms is the cell• Cells carry out the functions needed to

support life.• All cells arise from preexisting cells

(this principle discarded the idea of

spontaneous generation)

Why study cells?• Cells Tissues Organs Bodies

– bodies are made up of cells– cells do all the work of life!

The Work of Life• What jobs do cells have to do for an organism to live…

– “breathe” • gas exchange: O2 in vs. CO2 out

– eat• take in & digest food

– make energy• ATP

– build molecules• proteins, carbohydrates, fats, nucleic acids

– remove wastes – control internal conditions

• homeostasis

– respond to external environment– build more cells

• growth, repair, reproduction & development

ATP

• Cells provide structure and form to the body.

• They appear in a variety of shapes;

round, concave,

rectangular, tapered,

spherical, and other.

• Cell shape seems to

be related to

specialized function.

Cell Size (Varies)

Cells are:

• Unit of Function: Each cell is a living unit. A cell performs many metabolic functions to sustain life. Each cell is a biochemical factory using food molecules for energy; repair of tissues, growth and ultimately reproduction.

• Unit of Growth: Each living organism begins as a single cell. Some organisms such as a protist, remain unicellular. For a multicellular organism, as the number of cells increases in the body of a plant or animal, so too does its size.

• Unit of heredity: New cells only arise from preexisting cells. A cell grows to optimum size and then divides, producing either two cells identical to itself OR four cells not identical.

• Cells carry hereditary information from one generation to the next. This information is coded in molecules of DNA (deoxyribonucleic acid).

Characteristics of All Cells

• Have a surrounding membrane

• Cytoplasm – cell contents in thick fluid

• Organelles – structures for cell function

• Control center with DNA

Cell Types

• Prokaryotic

• Eukaryotic

Two Types of Cells

• Prokaryotes

• First cells to evolve

• No nucleus

• Hereditary info is contained within cytoplasm

• Ex. Bacteria

• Eukaryotes• Evolved from

Prokaryotes• Have a nucleus• Hereditary Info is

contained within the nucleus

• Ex. Plants, Animals, Fungi

Prokaryotic Cells

• First cell type on earth

• Cell type of Bacteria and Archaea

Prokaryotic Cells

• No membrane bound nucleus

• Nucleoid = region of DNA concentration

• Organelles not bound by membranes

Bacterium Shapes

Eukaryotic Cells• Nucleus bound by membrane

• Include fungi, protists, plant, and animal cells

• Possess many organelles

Protozoan

Representative Animal Cell

Representative Plant Cell

Organelles

• Cellular machinery

Cell Walls• Found in plants, fungi, & many protists• Surrounds plasma membrane• Made of cellulose • Is rigid • Provides support and

protection for the cell

Cell Wall Differences

• Plants – mostly cellulose

• Fungi – contain chitin

Cell membrane• Surrounds all cells• In a plant cell, it lies beneath the cell wall • – In animal cells, it is the outer boundary (made of

cholesterol) • Lipid bilayer with embedded proteins

• Provides cell with – Protection • Isolates the cell’s contents from external environment• Regulates the flow of materials into and out of the cell

(i.e. selectively permeable )• Allows interaction among cells•  Support

Cytoplasm• Viscous fluid containing organelles• components of cytoplasm

– Interconnected filaments & fibers – Fluid = cytosol

• Found in both plant and animal cells • Located beneath cell membrane • Supports and protects cell organelles

Organelles

• Functional components within cytoplasm

Nucleus• Function

– control center of cell– protects DNA

• instructions for building proteins

• Structure– nuclear membrane– nucleolus

• ribosome factory

– chromosomes• DNA

DNA

• Hereditary material

• Chromosomes

Nucleic Acid

• Deoxyribonucleic acid (DNA) has two functions:

• DNA controls protein synthesis in the cell

• DNA is replicated and passed on to progeny cells during reproduction

Nucleolus

• Most cells have 2 or more

• Directs synthesis of RNA

• Forms ribosomes

Endoplasmic Reticulum

• Helps move substances within cells

• Network of interconnected tubes

• Two types– Rough endoplasmic reticulum– Smooth endoplasmic reticulum

Rough Endoplasmic Reticulum

• Ribosomes attached to surface– Manufacture proteins– Not all ribosomes attached to rough ER

Smooth Endoplasmic Reticulum

• No attached ribosomes

• Has enzymes that help build molecules– Carbohydrates– Lipids

Endo-membrane System

transport vesicles

vesiclescarrying proteins

Golgi Apparatus• Function

– finishes, sorts, labels & ships proteins• like UPS headquarters

– shipping & receiving department

– ships proteins in vesicles• “UPS trucks”

• Structure– membrane sacs

Lysosomes

• Found only in animal cells• Contain digestive enzymes• Functions

– Aid in cell renewal– Break down old cell parts – Digests invaders

Lysosome

Peroxisome

• Similar to lysosome

• Membrane-bound vesicle that contains enzymes

• Enzymes are used to breakdown toxic substances to hydrogen peroxide

• Hydrogen peroxide is broken down by catalase to produce water and oxygen

Vacuoles

• Membrane bound storage sacs

• More common in plants than animals

• Contents – Water– Food– wastes

Mitochondria• Have their own DNA• Bound by double membrane• Has inner foldings (Cristae) that increase the internal surface

area

Mitochondria

• Break down fuel molecules (cellular respiration)

– Glucose– Fatty acids

• Release energy– ATP

Mitochondria• Function

– make ATP energy from cellular respiration• sugar + O2 ATP• fuels the work of life

in both animal & plant cellsin both animal & plant cells

ATP

Plants make energy two ways!

• Mitochondria– make energy from sugar + O2

• cellular respiration• sugar + O2 ATP

• Chloroplasts– make energy + sugar from sunlight

• photosynthesis

• sunlight + CO2 ATP & sugar– ATP = active energy– sugar = stored energy

» build leaves & roots & fruit out of the sugars

ATP

sugar

ATP

Chloroplasts

•Solar energy capturing organelle

Photosynthesis

• Takes place in the chloroplast

• Makes cellular food – glucose

Mitochondria are in both cells!!

animal cellsanimal cells plant cellsplant cells

mitochondriamitochondriachloroplastchloroplast

Cells need workers = proteins!

• Making proteins– to run daily life & growth, the cell must…

• read genes (DNA)• build proteins

– structural proteins (muscle fibers, hair, skin, claws)– enzymes (speed up chemical reactions)– signals (hormones) & receptors

– organelles that do this work…• nucleus • ribosomes• endoplasmic reticulum (ER) • Golgi apparatus

DNA

RNA

ribosomes

endoplasmicreticulum

vesicle

Golgi apparatus

vesicle

proteinon its way!

protein finishedprotein

Making Proteins

TO:

TO:

TO:

TO:

nucleus

Cells need to make more cells!

• Making more cells– to replace, repair & grow,

the cell must…• copy their DNA• make extra organelles

• divide the new DNA & new organelles between 2 new “daughter” cells

– organelles that do this work…• nucleus • centrioles

Centrioles• Function

– help coordinate cell division• only in animal cells

• Structure– one pair in each cell

Cell Summary• Cells have 3 main jobs

– make energy• need food + O2

• cellular respiration & photosynthesis• need to remove wastes

– make proteins• need instructions from DNA• need to chain together amino acids & “finish”

& “ship” the protein

– make more cells• need to copy DNA & divide it up to daughter cells

Our organellesdo all thosejobs!

Plasma Membrane

• Contains cell contents

• Double layer of phospholipids & proteins

Phospholipids

• Polar– Hydrophylic head– Hydrophobic tail

• Interacts with water

Movement Across the Plasma Membrane

• A few molecules move freely– Water, Carbon dioxide, Ammonia, Oxygen

• Carrier proteins transport some molecules– Proteins embedded in lipid bilayer– Fluid mosaic model – describes fluid nature of

a lipid bilayer with proteins

Molecule Movement & Cells

• Passive Transport

• Active Transport

• Endocytosis

(phagocytosis & pinocytosis)

• Exocytosis

Passive Transport

• No energy required

• Move due to gradient– differences in concentration, pressure, charge

• Move to equalize gradient– High moves toward low

Types of Passive Transport

1. Diffusion

2. Osmosis

3. Facilitated diffusion

Diffusion

• Molecules move to equalize concentration

Osmosis

• Special form of diffusion

• Fluid flows from lower solute concentration

• Often involves movement of water– Into cell– Out of cell

Solution Differences & Cells• solvent + solute = solution

• Hypotonic– Solutes in cell more than outside– Outside solvent will flow into cell

• Isotonic– Solutes equal inside & out of cell

• Hypertonic– Solutes greater outside cell– Fluid will flow out of cell

Facilitated Diffusion

• Differentially permeable membrane

• Channels (are specific) help molecule or ions enter or leave the cell

• Channels usually are transport proteins (aquaporins facilitate the movement of

water)• No energy is used

Process of Facilitated Transport

• Protein binds with molecule

• Shape of protein changes

• Molecule moves across membrane

Active Transport

• Molecular movement

• Requires energy (against gradient)

• Example is sodium-potassium pump

Endocytosis

• Movement of large material– Particles– Organisms – Large molecules

• Movement is into cells

• Types of endocytosis– bulk-phase (nonspecific)– receptor-mediated (specific)

Process of Endocytosis

• Plasma membrane surrounds material

• Edges of membrane meet

• Membranes fuse to form vesicle

Forms of Endocytosis

• Phagocytosis – cell eating

• Pinocytosis – cell drinking

Exocytosis

• Reverse of endocytosis

• Cell discharges material

Exocytosis

• Vesicle moves to cell surface

• Membrane of vesicle fuses

• Materials expelled

Membrane Proteins

1. Channels or transporters– Move molecules in one direction

2. Receptors – Recognize certain chemicals

Membrane Proteins

3. Glycoproteins – Identify cell type

4. Enzymes – Catalyze production of substances

Review of Eukaryotic Cells

Review of Eukaryotic Cells