CELL STRUCTURE AND FUNCTION

EARLY STUDIES LED TO THE DEVELOPMENT OF THE CELL THEORY

HISTORY OF CELL THEORY

• 1665 Robert Hooke: looked at cork-saw cell walls and named them “cells”

• 1674 Leeuwenhock: invented the 1st light microscope-saw first organisms using pond water

HISTORY OF CELL THEORY

• 1838 Scleiden: plants are made of cells!!

• 1839 Schwann: animals are made of cells!!

• 1855 Virchow: recognized dividing cells-all living things come from other cells!!

Cell Theory is Complete

CELL THEORY

• All organisms are made of cells

• All existing cells are produced by other living cells

• The cell is the most basic unit of life

SMALL CELL SIZE = GOOD

• Function more efficiently than large cells

• Substances do not have to travel as far to reach the center of a smaller cell

• Can exchange substances more readily than large cells

• Higher surface-to-volume ratio than larger cells

COMMON FEATURES OF CELLS

• Cell Membrane

• Cytoplasm

• Ribosomes

CYTOPLASM

• The region of the cell within the membrane that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus

• Jellylike

• In other words… the cell fluid

TWO MAJOR CELL TYPES

PROKARYOTIC VS. EUKARYOTIC

• Prokaryotic cell: cell that does not have a nucleus or other membrane-bound organelles

• Eukaryotic cell: cell that has a nucleus and other membrane-bound organelles

ORGANELLES

• Membrane-bound structure that is specialized to perform a distinct process within a cell

PROKARYOTIC CELLS LACK A NUCLEUS AND MOST

INTERNAL STRUCTURES OF EUKARYOTIC CELLS

PROKARYOTIC CELLS • Smallest, simplest cells

• Originated 3.5 billion years ago

• Single-celled organisms

• Can live in a broad range

of environmental conditions

CHARACTERISTICS OF PROKARYOTES

• No internal structures

– Enzymes and ribosomes are free to move in the cytoplasm

• Genetic Material

– Singular, circular molecule of DNA…NO NUCLEUS to contain it!!

• Cell wall

– A rigid structure that surrounds the cell membrane and provides support to the cell

• Flagella

– Long, hair-like structure that grows out of a cell and enables the cell to move

EUKARYOTIC CELLS: PLANT, ANIMAL, FUNGI & PROTIST

• Single celled or multi-celled organisms

• Organism whose cells have a nucleus

• Have organelles

EUKARYOTIC CELLS

• Many single-celled eukaryotes move:

• Flagella

• Cilia – Example: cilia in

human respiratory tract moves mucus out of lungs

ANIMAL CELLS

white blood cell

red blood cell

cheek cells sperm

nerve cell

muscle cell

Amoeba

Paramecium

CELLS HAVE AN INTERNAL STRUCTURE

• Cytoskeleton: network of proteins, such as microtubules and microfilaments, inside a eukaryotic cell

• Supports and shapes cell

• Role in cell movement and division

THE CYTOSKELETON… A WEB OF PROTEIN FIBERS

• Actin Fibers

• Major role in determining the SHAPE of animal cells

THE CYTOSKELETON… A WEB OF PROTEIN FIBERS

• Microtubules

• Transport route of information from the nucleus to different cell parts

THE CYTOSKELETON… A WEB OF PROTEIN FIBERS

• Intermediate Fibers

• Stabilize organelles

NUCLEUS

• Organelle composed of a double membrane that acts as the storehouse for most of a cell’s DNA

• DNA – Hereditary information stored in the

nucleus – Found in the form of long strands called

chromosomes

THE NUCLEUS… THE CONTROL CENTER

• Nuclear envelope: double membrane that surrounds the nucleus

• Nuclear pores: small channels in the nuclear envelope

• Items made in the nucleus exit to the cytoplasm

• Nucleolus: location where ribosomes are made

ENDOPLASMIC RETICULUM (ER)

• Interconnected network of thin, folded membranes that produce, process, and distribute proteins

• Found in a cell’s cytoplasm

• Assists in the production of lipids

THE ER

• Rough ER

• Part of the ER with ribosomes attached

• Where proteins are made and released by a vesicle

THE ER

• Smooth ER

• Part of the ER that lacks ribosomes

• Where steroids are created and stored

RIBOSOMES

• Organelle that links amino acids together to form proteins

• Composed of RNA and protein

• Can be free-floating or attached to the ER

GOLGI APPARATUS

• Stack of flat, membrane-enclosed spaces containing enzymes that process, sort, and deliver proteins

• Helps make and package materials to be transported out of the cell

VESICLES

• Small organelle that contains and transports materials within the cytoplasm

SEVERAL ORGANELLES ARE INVOLVED IN MAKING AND

PROCESSING PROTEINS

PACKING & DISTRIBUTION OF PROTEINS

• Ribosomes make proteins (Where? The rough

ER)

• The proteins are packaged into vesicles

• The vesicles transport the newly made proteins (Where? rough ER Golgi apparatus)

• In the Golgi apparatus, proteins are processed and then packaged into new vesicles

PACKING & DISTRIBUTION OF PROTEINS

• Many of these vesicles move to the cell

membrane and release their contents outside the cell

• Other vesicles, including lysosomes, remain within the cytoplasm

• Lysosomes digest and recycle the cell’s used components by breaking down proteins, nucleic acids, lipids, and carbohydrates

MITOCHONDRION (A)

• Bean-shaped organelle, surrounded by two membranes

• Site of cellular respiration

• Supplies energy (ATP) to the cell

• Has its own ribosomes to make its own proteins and has its own DNA

• Endosymbiosis Theory

VACUOLE

• Organelle that is used to store materials such as water, food, or enzymes, that are needed by the cell

CENTRAL VACUOLE • Found in plant cells or

protozoans

• Contains air or partially digested food

• Stores water

• Can contain ions, nutrients and/or waste

• When it is full, the cell becomes rigid, enabling the plant to stand upright

LYSOSOME

• Organelle that contains enzymes

CELL WALL

• Rigid structure that gives protection, support, and shape to cells in – Plants

– Algae

– Fungi

– Bacteria

CELL WALL

• Surrounds the cell membrane

• Composed of proteins and carbohydrates, including the polysaccharide cellulose

CELL WALL

• Provides support to the cell

• Helps maintain cell shape

• Protects the cell from damage

• Connects cell with adjacent cells

CHLOROPLASTS…SITE OF PHOTOSYNTHESIS

• Use light energy to make carbohydrates from carbon dioxide and water

• Also found in eukaryotic algae, such as seaweed

CHLOROPLASTS…SITE OF PHOTOSYNTHESIS

• Supply much of the energy to power plant cells

• Surrounded by two membranes, contain their own DNA

CELL MEMBRANE

• Double-layer of phospholipids

• Forms a boundary between a cell and the surrounding environment

• Controls the passage of materials into and out of a cell

PHOSPHOLIPID

• Molecule that forms a double-layered cell membrane

• Consists of: – a glycerol molecule

– a phosphate group

– two fatty acids

CELL MEMBRANES ARE COMPOSED OF TWO

PHOSPHOLIPID LAYERS

FLUID MOSAIC MODEL

• Model that describes the arrangement and movement of the molecules that make up a cell membrane

MRS. B’S INTERPRETATION OF THE FLUID MOSAIC MODEL

MEMBRANE PROTEINS “FLUID-MOSAIC MODEL”

• How are proteins held in the membrane?

• Flashback: some amino acids are polar, some are nonpolar

• Nonpolar part of membrane protein is attracted to the interior of the lipid bilayer

• Polar part of the membrane protein is attracted to the water on the exterior of the lipid bilayer

THE CELL MEMBRANE… THE SELECTIVELY-PERMEABLE

BARRIER!

• Phospholipid Bilayer

• Phosphate group

• 2 fatty acids

PHOSPHOLIPID BILAYER

• Interior nonpolar tails

• Exterior polar heads

• Allows lipids and substances that dissolve in lipids to pass through

• Ions and most polar molecules are repelled by the nonpolar interior of the lipid bilayer

SELECTIVE PERMEABILITY

• Condition or quality of allowing some, but not all, materials to cross a barrier or membrane

CHEMICAL SIGNALS ARE TRANSMITTED ACROSS

THE CELL MEMBRANE

MEMBRANE PROTEINS

• Marker Protein

• Attach to a carbohydrate on the cell’s surface

• Advertise cell type-i.e. liver cell, heart cell

MEMBRANE PROTEINS

• Receptor Protein

• Bind specific substances, such as signal molecules, outside the cell

MEMBRANE PROTEINS

• Enzyme

• Involved in important biochemical reactions in the cell

MEMBRANE PROTEINS

• Transport Protein

• Aid in the movement of substances into and out of the cell

SIGNAL MOLECULES

• Molecules that carry information to and from nearby cells and throughout the body

• Example: Hormones…Made in one part of the body and transported in the blood stream where they have their effects

RECEPTOR PROTEINS

• A protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule

• Example: The muscles of a person exercising would not contract without receptor proteins and signal molecules to tell the muscles when to contract and when to relax.

FUNCTIONS OF RECEPTOR PROTEINS

• Changes in Permeability

• Second Messengers

• Enzyme Action

DIFFUSION

• The movement of a substance from an area of high concentration to an area of lower concentration

RANDOM MOTION AND CONCENTRATION

• Concentration gradient: the difference in the concentration of a substance across a distance

• Equilibrium:

concentration of a substance is equal throughout a space

BACK TO THE CELL MEMBRANE

• It is Selectively Permeable!!

• Allows Readily: – Very small molecules – Nonpolar molecules

• Does Not Allow Readily: – Large molecules – Polar molecules

PASSIVE TRANSPORT

• The movement of substances across a cell membrane

• Without the use of energy

• Very small molecules

• Nonpolar molecules

DIFFUSION THROUGH ION CHANNELS

• Transport proteins with a polar pole through which ions can pass

• Some pores are always open

• Some pores can be closed by ion channel gates

OSMOSIS

• The diffusion of water through a selectively permeable membrane

• LOWER SOLUTE concentration HIGHER SOLUTE concentration

HYPERTONIC SOLUTION

• A solution whose solute concentration is higher than the solute concentration inside a cell

• Water moves out of the cell and the cell shrinks

HYPOTONIC SOLUTION

• A solution whose solute concentration is lower than the solute concentration inside a cell

• Water moves into the cell and the cell swells or bursts

ISOTONIC SOLUTION

• A solution whose solute concentration is equal to the solute concentration inside a cell

• Water flows into and out of the cell at equal rates

Isotonic Hypertonic Hypotonic

WATER MOVES: HYPOTONIC HYPERTONIC

SOME MOLECULES DIFFUSE THROUGH TRANSPORT PROTEINS

• Facilitated diffusion: diffusion of molecules assisted by protein channels that pierce a cell membrane

DIFFUSION AND OSMOSIS ARE TYPES OF PASSIVE

TRANSPORT

ACTIVE TRANSPORT

• The movement of chemical substances, usually across the cell membrane, against a concentration gradient

• Requires cells to use energy – Large molecules

– Polar molecules

PROTEINS CAN TRANSPORT MATERIALS AGAINST A

CONCENTRATION GRADIENT

SODIUM-POTASSIUM (NA+-K+) PUMP

• 3 Na+ out of the cell (more abundant outside) • 2 K+ into the cell (more abundant inside) • Therefore…this is ACTIVE TRANSPORT

ENDOCYTOSIS AND EXOCYTOSIS TRANSPORT MATERIALS ACROSS THE MEMBRANE IN VESICLES

MOVEMENT IN VESICLES

ENDOCYTOSIS

• Cell membrane surrounds a particle and encloses it in a vesicle to bring into the cell

ENDOCYTOSIS

• Pinocytosis –Liquid being taken in by

endocytosis

• Phagocytosis –Large particles being

taken in by endocytosis

EXOCYTOSIS

• A substance is released from the cell through a vesicle

• The vesicle transports the substance to the cell surface and then fuses with the membrane to let the substance out