Cell Structure and Function

1 KEDALAMAN KAJIAN BIOMEDIK

2 Cell Structure and Function

Cell Structure

^• In 1655, the English scientist Robert Hooke coined the term “cellulae” for the small box-like structures he saw while examining a thin slice of cork under a microscope.

All cells have the following basic structure:
A thin, flexible
The interior is filled with a semi-fluid
Also inside are specialized structures

4 Basic Cell Structure

Basic Cell Structure

All cells have the following basic structure:

A thin, flexible plasma membrane plasma membrane surrounds the entire cell. surrounds the entire cell.

The interior is filled with a semi-fluid material called the material called the cytoplasm cytoplasm .

Also inside are specialized structures called organelles and the cell’s called organelles and the cell’s genetic genetic material. material.

5 Generalized Eukaryotic Cell

6 Visualizing Cells

Prokaryotic Cells

^• Simplest organisms ^–

Cytoplasm is surrounded by plasma membrane and

encased in a rigid cell wall composed of peptidoglycan. ^– No distinct interior compartments ^– Some use flagellum for locomotion, threadlike structures protruding from cell surface

Characterized by compartmentalization by
an endomembrane system, and the
presence of membrane-bound organelles.
_– central vacuole _– vesicles _– chromosomes _– cytoskeleton _– cell walls

8 Eukaryotic Cells

9 Animal cell anatomy Animal Cell

Membrane Function Membrane Function

_•

carbohydrate groups join

function as cell identity

glycoproteins. These

proteins to form

glycolipids, and with

with lipids to form

carbohydrate groups join

On the external surface,

All cells are surrounded

On the external surface,

proteins embedded in the bilayer. bilayer. _•

proteins embedded in the

bilayer with globular

composed of a lipid

Cell membranes are

All cells are surrounded by a plasma membrane. by a plasma membrane. _•

function as cell identity markers. markers.

Fluid Mosaic Model Fluid Mosaic Model

_•

In 1972, S. Singer and G. Nicolson proposed the Fluid

Mosaic Model of membrane structure

Mosaic Model of membrane structure _{Extracellular fluid} Carbohydrate ^Glycolipid

Transmembrane ^Glycoprotein _proteins _Peripheral protein ^Cholesterol _{Filaments of} _cytoskeleton ^Cytoplasm

Phospholipids Phospholipids

Glycerol

Glycerol

Two fatty acids

Two fatty acids

Phosphate group Hydrophilic _heads Hydrophobic _tails ^{ECF WATER}

Phosphate group

Phospholipid Bilayer Phospholipid Bilayer

^• Mainly 2 layers of phospholipids; the non-polar tails

Mainly 2 layers of phospholipids; the non-polar tails point inward and the polar heads are on the surface. _• point inward and the polar heads are on the surface.

Contains cholesterol in animal cells.

^• Is fluid, allowing proteins to move around within the

Is fluid, allowing proteins to move around within the bilayer. bilayer. Polar _heads _hydro-philic _tails _hydro-phobic Nonpolar _heads _hydro-philic Polar Effects on membrane fluidity within the animal cell membrane the animal cell membrane

Cholesterol

Steroid Cholesterol Steroid Cholesterol

Effects on membrane fluidity within

A membrane is a collage of different proteins
Peripheral proteins are appendages loosely

Glycoprotein _Carbohydrate Microfilaments _{of cytoskeleton} _{Cholesterol Peripheral} _protein _Integral _protein ^Glycolipid

Membrane Proteins Membrane Proteins

A membrane is a collage of different proteins

embedded in the fluid matrix of the lipid bilayer

Peripheral proteins are appendages loosely

bound to the surface of the membrane

bound to the surface of the membrane _{Fibers of extracellular} _{matrix (ECM)}

Integral proteins Integral proteins

Penetrate the hydrophobic core of the lipid bilayer lipid bilayer

Penetrate the hydrophobic core of the

Are often transmembrane proteins, completely spanning the membrane completely spanning the membrane _{EXTRACELLULAR}

Are often transmembrane proteins,

SIDE ^N-terminus C-terminus _{ Helix} _CYTOPLASMIC _SIDE

Functions of Cell Membranes Functions of Cell Membranes

Regulate the passage of substance into and out of cells and between cell into and out of cells and between cell organelles and cytosol organelles and cytosol

Regulate the passage of substance

Detect chemical messengers arriving at the surface at the surface

Detect chemical messengers arriving

Link adjacent cells together by membrane junctions membrane junctions

Link adjacent cells together by

Anchor cells to the extracellular matrix matrix

Anchor cells to the extracellular

6 Major Functions Of Membrane

6 Major Functions Of Membrane Proteins _{1. Transport. (left) A protein that spans the membrane} Proteins _{(right) Other transport proteins shuttle a substance} _{membrane that is selective for a particular solute.} may provide a hydrophilic channel across the _{actively pump substances across the membrane} _{these proteins hydrolyze ATP as an energy ssource to} from one side to the other by changing shape. Some of _ATP _{2. Enzymatic activity. A protein built into the membrane} _{substances in the adjacent solution. In some cases,} _{may be an enzyme with its active site exposed to} Enzymes _pathway. _{team that carries out sequential steps of a metabolic} several enzymes in a membrane are organized as a _{3. Signal transduction. A membrane protein may have a} _{chemical messenger, such as a hormone. The external} _{binding site with a specific shape that fits the shape of a} Signal _{inside of the cell.} _{in the protein (receptor) that relays the message to the} messenger (signal) may cause a conformational change Receptor

Cell-cell recognition. Some glyco-proteins serve as _{identification tags that are specifically recognized} _{by other cells.}

Intercellular joining. Membrane proteins of adjacent cells _{may hook together in various kinds of junctions, such as} _{gap junctions or tight junctions} Attachment to the cytoskeleton and extracellular matrix _{(ECM). Microfilaments or other elements of the} _{cytoskeleton may be bonded to membrane proteins,} a function that helps maintain cell shape and stabilizes _{the location of certain membrane proteins. Proteins that} _{adhere to the ECM can coordinate extracellular and} intracellular changes ^4. ^5. ^6. ^Glyco- ^protein

6 Major Functions Of Membrane Proteins

_Outside Functions of Plasma Membrane Proteins _membrane Plasma Inside _{Transporter Enzyme} _{Cell surface} _receptor

Cell surface identity _marker _{Cell adhesion} ^{Attachment to the} _cytoskeleton

The plasma membrane is the boundary that

In order to survive, A cell must exchange
Materials must enter and leave the cell through
Membrane structure results in selective

it more easily than others

permeability, it allows some substances to cross

Membrane structure results in selective

Materials must enter and leave the cell through the plasma membrane. the plasma membrane.

controlled by the plasma membrane

materials with its surroundings, a process

In order to survive, A cell must exchange

surroundings

separates the living cell from its nonliving

The plasma membrane is the boundary that

Membrane Transport Membrane Transport

it more easily than others

The plasma membrane exhibits selective permeability - It allows some selective permeability - It allows some substances to cross it more easily substances to cross it more easily than others than others

Membrane Transport Membrane Transport

The plasma membrane exhibits

Passive Transport Passive Transport

Passive transport is diffusion of a substance across a membrane with substance across a membrane with no energy investment no energy investment

Passive transport is diffusion of a

4 types

4 types

Simple diffusion

Simple diffusion
Dialysis

Dialysis

Osmosis

Osmosis
Facilitated diffusion

Facilitated diffusion Solution – homogeneous mixture of two or more components two or more components

Solutions and Transport Solutions and Transport

Solution – homogeneous mixture of

Solvent – dissolving medium

Solvent – dissolving medium

Solutes – components in smaller quantities within a solution within a solution

Solutes – components in smaller quantities

Intracellular fluid – nucleoplasm and cytosol cytosol

Intracellular fluid – nucleoplasm and

Extracellular fluid

Extracellular fluid

Interstitial fluid – fluid on the exterior of the cell within tissues within tissues

Interstitial fluid – fluid on the exterior of the cell

Plasma – fluid component of blood

Plasma – fluid component of blood

Lump _{of sugar} No net movement at ^{Random movement leads to}

^{net movement down a}

^{concentration gradient}

^Water

Diffusion Diffusion

_•

_{The net movement of a substance from an area of higher The net movement of a substance from an area of higher}

_• concentration to an area of lower concentration - down a concentration to an area of lower concentration - down a _{concentration gradient} _{concentration gradient} Caused by the constant random motion of all atoms and molecules

^{Caused by the constant random motion of all atoms and molecules}

_•

_{Movement of individual atoms & molecules is random, but each}

^{substance moves down its own concentration gradient.}

Net diffusion Net diffusion ^Equilibrium

Diffusion Across a Membrane Diffusion Across a Membrane

_•

_{The membrane has pores large enough for the molecules to pass The membrane has pores large enough for the molecules to pass}

_•

_{Random movement of the molecules will cause some to pass}

through the pores; this will happen more often on the side with more

^{through the pores; this will happen more often on the side with more}

_{molecules. The dye diffuses from where it is more concentrated to}

_{where it is less concentrated}

_{This leads to a dynamic equilibrium: The solute molecules continue} _{This leads to a dynamic equilibrium: The solute molecules continue} _{to cross the membrane, but at equal rates in both directions.} _{to cross the membrane, but at equal rates in both directions.}

the left side ^{the left side} Net diffusion _{Net diffusion}

^{Net diffusion}

_{Net diffusion}

_Equilibrium

^Equilibrium

Diffusion Across a Membrane Diffusion Across a Membrane

_•

_{Two different solutes are separated by a membrane that is Two different solutes are separated by a membrane that is}

_• permeable to both permeable to both _{Each solute diffuses down its own concentration gradient.} _{Each solute diffuses down its own concentration gradient.}
_{There will be a net diffusion of the purple molecules toward the left,} _{There will be a net diffusion of the purple molecules toward the left,} _{even though the total solute concentration was initially greater on} _{even though the total solute concentration was initially greater on}

Permeability Factors

Hydrophobic molecules are lipid soluble and can

substances across the membrane

Transport proteins allow passage of hydrophilic

rapidly

Polar molecules do not cross the membrane

pass through the membrane rapidly

Presence of channels and transporters

Charge _•

Charge

Size _•

Size

Lipid solubility _•

Permeability Factors _• Lipid solubility

The Permeability of the Lipid Bilayer The Permeability of the Lipid Bilayer

Hydrophobic molecules are lipid soluble and can
Polar molecules do not cross the membrane
Transport proteins allow passage of hydrophilic

substances across the membrane

Passive Transport Processes Passive Transport Processes _• _{3 special types of diffusion} _{3 special types of diffusion} that involve movement of ^{that involve movement of} _{materials across a} _{materials across a} _{semipermeable membrane semipermeable membrane}

_{Dialysis/selective diffusion} _{Dialysis/selective diffusion} _{of solutes} _{of solutes} _• _{Lipid-soluble materials} _{Lipid-soluble materials}
_{Small molecules that} _{Small molecules that} _{can pass through} _{can pass through} _{membrane pores} _{membrane pores}
_• unassisted ^unassisted _{Facilitated diffusion -} _{Facilitated diffusion -} _{substances require a substances require a} protein carrier for passive
_• ^{protein carrier for passive} _transport _transport _{Osmosis – simple diffusion} _{Osmosis – simple diffusion} of water

^{of water}

Osmosis Osmosis

Diffusion of the solvent across a semipermeable membrane. semipermeable membrane.

Diffusion of the solvent across a

In living systems the solvent is always water, so biologists always water, so biologists generally define osmosis as the generally define osmosis as the diffusion of water across a diffusion of water across a semipermeable membrane: semipermeable membrane:

In living systems the solvent is

Osmosis _Lower _Higher Osmosis _{of solute (sugar) of sugar} _{concentration concentration}

_{of sugar}

_{permeable mem-}

_{cules cannot pass}

_{brane: sugar mole-}

_{Water molecules}

_{sugar molecules}

_{cluster around}

_{water molecules can}

_{molecules (higher}

_{More free water}

_{Fewer free water}

_{concentration)}

_Osmosis

_{concentration)}

_{of lower free water concentration}

_{free water concentration to an area}

_{Water moves from an area of higher}

Osmotic Pressure Osmotic Pressure

Osmotic pressure of a solution is the pressure needed to keep it in pressure needed to keep it in equilibrium with pure H20. equilibrium with pure H20.

Osmotic pressure of a solution is the

The higher the concentration of solutes in a solution, the higher its solutes in a solution, the higher its osmotic pressure. osmotic pressure.

The higher the concentration of

Tonicity is the ability of a solution to cause a cell to gain or lose water – cause a cell to gain or lose water – based on the concentration of solutes based on the concentration of solutes

Tonicity is the ability of a solution to

Tonicity Tonicity

_•

If 2 solutions have equal [solutes], they are called

_• isotonic

isotonic

If one has a higher [solute], and lower [solvent], is

_• hypertonic

hypertonic

The one with a lower [solute], and higher [solvent], is

hypotonic

hypotonic Hypotonic solution _{Isotonic solution} ^{Hypertonic solution}

H ₂ Ô ^H ² Ô ^H ² Ô ^H ² Ô Lysed ^{Normal Shriveled}

Water Balance In Cells With Walls Water Balance In Cells With Walls (b) Plant cell. Plant cells _{generally healthiest in} _{a hypotonic environ-} _{are turgid (firm) and} _{H O} ₂ _{H O} ₂ _{H O H O} ₂ ₂ _{by the elastic wall} _{eventually balanced} _{uptake of water is} ment, where the _cell. pushing back on the _{Turgid (normal) Flaccid} _Plasmolyzed

My definition of Osmosis My definition of Osmosis

Osmosis is the diffusion of water across a semi-permeable membrane across a semi-permeable membrane from a hypotonic solution to a from a hypotonic solution to a hypertonic solution hypertonic solution

Osmosis is the diffusion of water

Facilitated Diffusion

_•

_{Diffusion of solutes through a semipermeable membrane with the Diffusion of solutes through a semipermeable membrane with the}

_{that cannot pass through phospholipid bilayer.}

_•

^{Two types of transport proteins can help ions and large polar}

_{molecules diffuse through cell membranes:}

_•

_{Channel proteins – provide a narrow channel for the substance to pass}

_•

_{Carrier proteins – physically bind to the substance on one side of Carrier proteins – physically bind to the substance on one side of}

_{membrane and release it on the other.}

EXTRACELLULAR _FLUID Channel protein ^Solute _CYTOPLASM _{Carrier protein} ^Solute

Facilitated Diffusion Facilitated Diffusion

Specific

Specific

– each channel or carrier
– each channel or carrier

transports certain ions or molecules transports certain ions or molecules only only

Passive

Passive

– direction of net movement
– direction of net movement

is always down the concentration is always down the concentration gradient gradient

Saturates

Saturates

– once all transport
– once all transport

proteins are in use, rate of diffusion proteins are in use, rate of diffusion cannot be increased further cannot be increased further Uses energy (from ATP) to move a substance against its natural tendency substance against its natural tendency e.g. up a concentration gradient. e.g. up a concentration gradient.

Active Transport Active Transport

Uses energy (from ATP) to move a

Requires the use of carrier proteins

(transport proteins that physically bind to

Requires the use of carrier proteins

(transport proteins that physically bind to

2 types:

2 types:

Membrane pump (protein-mediated active transport) transport)

Membrane pump (protein-mediated active

Coupled transport (cotransport).

Coupled transport (cotransport).

ATP to move a substance across a membrane, up its concentration membrane, up its concentration gradient: gradient:

Membrane Pump Membrane Pump

A carrier protein uses energy from

The Sodium-potassium Pump The Sodium-potassium Pump

One type of active transport system

₊ ₊ ^•

One type of active transport system _{[K ] low} _{[Na ] high}

⁺ _{to the sodium-potassium} _pump. ₊ _Na ₊ ₊

_{1. Cytoplasmic Na binds}

_Na

_{EXTRACELLULAR}

_{FLUID Na}

_Na

_{[Na ] low ATP}

₊

⁺

_Na

_{2. Na+ binding stimulates}

_{phosphorylation by ATP.}

_CYTOPLASM

[K ] high ADP

⁺

_{6. K is released and Na}

_{sites are receptive again;}

₊ ₊ _{the cycle repeats.} _{+ +}

_Na

_{protein to change its conformation,}

_{3. Phosphorylation causes the}

₊

⁺

⁺ expelling Na to the outside. ₊ ⁺

_{5. Loss of the phosphate}

₊

_{original conformation.}

_{restores the protein’s}

_{K Phosphate group.}

_{protein, triggering release of the}

_{4. Extracellular K binds to the}

₊

P _i _P _P _i

Coupled transport Coupled transport

_•

2 stages:

2 stages: _• _{Carrier protein uses ATP to move a substance across the} _{Carrier protein uses ATP to move a substance across the}

membrane against its concentration gradient. Storing energy.

^{membrane against its concentration gradient. Storing energy.}

_•

_{Coupled transport protein allows the substance to move down its}

^{concentration gradient using the stored energy to move a}

_{second substance up its concentration gradient:}

Review: Passive And Active Transport Compared Review: Passive And Active Transport Compared

Passive transport. Substances diffuse spontaneously _{down their concentration gradients, crossing a} _{membrane with no expenditure of energy by the cell.} _{The rate of diffusion can be greatly increased by transport} _{proteins in the membrane.} _{Active transport. Some transport proteins act} _{as pumps, moving substances across a} _{membrane against their concentration} _{gradients. Energy for this work is usually} supplied by ATP.

Diffusion. Hydrophobic _{molecules and (at a slow} _{rate) very small uncharged} _{polar molecules can diffuse} _{through the lipid bilayer.} _{Facilitated diffusion. Many} _{hydrophilic substances diffuse} _{through membranes with the} _{assistance of transport proteins,} _{either channel or carrier proteins.} ^ATP

Bulk Transport Bulk Transport

Allows small particles, or groups of molecules to enter or leave a cell molecules to enter or leave a cell without actually passing through the without actually passing through the membrane. membrane.

Allows small particles, or groups of

2 mechanisms of bulk transport: endocytosis and exocytosis. endocytosis and exocytosis.

2 mechanisms of bulk transport:

Endocytosis Endocytosis

The plasma membrane envelops small particles or fluid, then seals on small particles or fluid, then seals on itself to form a vesicle or vacuole itself to form a vesicle or vacuole which enters the cell: which enters the cell:

The plasma membrane envelops

Phagocytosis

Phagocytosis
Pinocytosis

Pinocytosis

Receptor-Mediated Endocytosis -

Receptor-Mediated Endocytosis -

Three Types Of Endocytosis Three Types Of Endocytosis EXTRACELLULAR _FLUID _Pseudopodium _CYTOPLASM

“Food” or _{other particle} _Food vacuole ^Pseudopodium ^{1 µm} ^{of amoeba} ^Bacterium ^{Food vacuole} _{An amoeba engulfing a bacterium via} _{phagocytosis (TEM).} _PINOCYTOSIS Pinocytosis vesicles _{forming (arrows) in} _{a cell lining a small} _{blood vessel (TEM).} ^{0.5 µm} ^{In pinocytosis, the cell} ^{“gulps” droplets of} ^{extracellular fluid into tiny} ^{vesicles. It is not the fluid} _{itself that is needed by the} _{cell, but the molecules} _{dissolved in the droplet.}

Because any and all _{included solutes are taken} _{into the cell, pinocytosis} _{is nonspecific in the} substances it transports. ^Plasma ^membrane ^Vesicle ^{In phagocytosis, a cell} ^{engulfs a particle by} ^{Wrapping pseudopodia} ^{around it and packaging} ^{it within a membrane-} ^{enclosed sac large} ^{enough to be classified} ^{as a vacuole. The} ^{particle is digested after} ^{the vacuole fuses with a} ^{lysosome containing} ^{hydrolytic enzymes.} ^PHAGOCYTOSIS

Process of Phagocytosis Process of Phagocytosis

Receptor-mediated Endocytosis Receptor-mediated Endocytosis _{Receptor-mediated endocytosis} _{enables the cell to acquire bulk quantities} _Receptor Coat protein _vesicle _Coated _{substances may not be very concentrated} of specific substances, even though those _{membrane are proteins with specific} _{in the extracellular fluid. Embedded in the} _{membrane called coated pits, which are} _{already clustered in regions of the} _{fluid. The receptor proteins are usually} receptor sites exposed to the extracellular _Coated _pit _{layer of coat proteins.} _{Extracellular substances (ligands) bind} lined on their cytoplasmic side by a fuzzy _{to these receptors. When binding occurs,} _Coat _Ligand _{relatively more bound molecules (purple)} _are _{the ligand molecules. Notice that there} _{the coated pit forms a vesicle containing} protein _vesicle _{and a coated} _{A coated pit} inside the vesicle, other molecules _{(green) are also present. After this} _{vesicle, the receptors are recycled to the} _{ingested material is liberated from the} _receptor- _during _formed _{plasma membrane by the same vesicle.} _membrane

_Plasma

_{0.25 µm}

_(TEMs).

_endocytosis

Exocytosis Exocytosis

The reverse of endocytosis

The reverse of endocytosis

During this process, the membrane of a vesicle

During this process, the membrane of a vesicle

fuses with the plasma membrane and its

contents are released outside the cell:

Cell Junctions

Long-lasting or permanent connections between

^•

_{TIGHT JUNCTIONS}

_{Tight junctions prevent}

_{across a layer of cells}

_{fluid from moving}

_{Tight junction}

_{against each other, bound together by}

_{neighboring cells are very tightly pressed}

tight junctions

_{ous seals around the cells, tight junctions}

_{specific proteins (purple). Forming continu-}

_{0.5 µm}

_{A layer of epithelial cells.}

_DESMOSOMES

_Intermediate

_filaments

_{Tight junctions}

_{Anchor desmosomes in the cytoplasm.}

_{Together into strong sheets. Intermediate}

_{junctions) function like rivets, fastening cells}

Desmosomes

anchoring

_{Filaments made of sturdy keratin proteins}

Desmosome _Gap _junctions _{1 µm} _{GAP JUNCTIONS} _{matrix surround a pore through which ions, sugars,} _{Extracellular consist of special membrane proteins that} _{one cell to an adjacent cell. Gap junctions} _{junctions) provide cytoplasmic channels from} Gap junctions (also called communicating

Space _cells _between _{of adjacent cells} _{Plasma membranes} _{Gap junction amino acids, and other small molecules may} _{0.1 µm} _{including heart muscle and animal embryos.} _{nication between cells in many types of tissues,} _{pass. Gap junctions are necessary for commu-}

_• _{Repository for genetic material called chromatin - DNA and proteins} _•

The Nucleus And The Nuclear Envelope _{Nucleolus: holds chromatin and ribosomal subunits - region of intensive} _{membranes - Double membrane with pores} _• _{Nuclear envelope: Surface of nucleus bound by two phospholipid bilayer} ribosomal RNA synthesis _Nucleus ^• Nucleoplasm: semifluid medium inside the nucleus _{1 µm} _{Nuclear envelope:} _{Inner membrane} _Chromatin _Nucleolus Nucleus

Outer membrane _{Nuclear pore} _{Surface of nuclear} Pore _complex _{Rough ER} _{envelope. Ribosome} _{0.25 µm} _nuclear _{Close-up of} 1 µm _{Pore complexes (TEM).}

envelope

_{Nuclear lamina (TEM).}

₅₀

Chromosomes

^•

^–

Exist as strands of chromatin, except

^–

52 Ribosomes _• Ribosomes are RNA-protein complexes composed of two subunits that join and attach to messenger RNA. _– Site of protein synthesis

_– Assembled in nucleoli _ER _Ribosomes

_Cytosol

Free ribosomes Bound ribosomes _Large _subunit Small _{TEM showing ER and ribosomes Diagram of a ribosome} _subunit _{0.5 µm} ^{Endoplasmic reticulum (ER)}

53 Endomembrane System _• Compartmentalizes cell, channeling passage of molecules through cell’s interior. _–

Endoplasmic reticulum _ Rough ER - studded with ribosomes _ Smooth ER - few ribosomes

_– _{Rough ER is especially abundant in cells that secrete proteins.} _{As a polypeptide is synthesized on a ribosome attached to rough ER, it is threaded into the} _•

Rough ER _– _{As it enters the cisternal space, the new protein folds into its native conformation.} cisternal space through a pore formed by a protein complex in the ER membrane. _–

_{Most secretory polypeptides are glycoproteins, proteins to which a carbohydrate is attached.}

_–

_{Enzymes in the rough ER also synthesize phospholipids from precursors in the cytosol.}

_•

_{Rough ER is also a membrane factory.}

_{Membrane-bound proteins are synthesized directly into the membrane.}

_–

transport vesicles

^–

_{components of the endomembrane system.}

_{These include the sex hormones of vertebrates and adrenal steroids.} _• _{In the smooth ER of the liver, enzymes help detoxify poisons and drugs such as} _{alcohol and barbiturates.}
_{Smooth ER stores calcium ions.} _ _{Muscle cells have a specialized smooth ER that pumps calcium ions from} _{the cytosol and stores them in its cisternal space.}

55 Smooth ER _• _{The smooth ER is rich in enzymes and plays a role in a variety of metabolic processes.} _• _{Enzymes of smooth ER synthesize lipids, including oils, phospholipids, and steroids.}

 _{When a nerve impulse stimulates a muscle cell, calcium ions rush from} _{the ER into the cytosol, triggering contraction.}

_products. _• _{The Golgi apparatus is the shipping and receiving center for cell} The Golgi apparatus _–

_{The Golgi is a center of manufacturing, warehousing, sorting, and}

_{modification of their contents.}

^–

Golgi apparatus

_{—looking like a stack of pita bread.}

_–

_{The Golgi apparatus consists of flattened membranous sacs—cisternae}

^–

56 Functions Of The Golgi Apparatus _{(“receiving” side of} _{cis face} Golgi _apparatus Golgi apparatus) _{6 Vesicles also} _{transport certain} _{proteins back to ER Cisternae}

1 Vesicles move _{from ER to Golgi} ^{2 Vesicles coalesce to} _{form new cis Golgi cisternae} _{0.1 0 µm}

3 Cisternal

_{Golgi cisternae}

_maturation:

_{move in a cis-}

_{leave Golgi, carrying}

_direction

_{4 Vesicles form and}

trans

₅

_{Vesicles transport specific}

_{trans face}

_{brane for secretion}

_{the plasma mem-}

_{other locations or to}

_{Golgi cisternae}

_{proteins backward to newer}

_{Golgi apparatus)}

_{TEM of Golgi apparatus}

₅₇

Membrane Bound Organelles Nucleus 1 µm

^• Lysosomes – vesicle containing digestive enzymes that break down food/foreign particles _Lysosome _{Lysosome contains} _{Food vacuole} ^•

Vacuoles – food storage _Hydrolytic and water regulation _{active hydrolytic fuses with} _{enzymes lysosome} _{food particles} ^{enzymes digest} ^• Peroxisomes - contain _enzymes _Digestive enzymes that catalyze the _{Plasma membrane} _Lysosome removal of electrons and _{Food vacuole} _Digestion associated hydrogen atoms _{(a) Phagocytosis: lysosome digesting food}

_• _{Sites of cellular respiration, ATP synthesis}

Mitochondria

_•

_{The inner membranes of mitochondria are cristae}

^•

_{the cristae house protein complexes that produce ATP}

^•

matrix

Cytoskeleton

^• The eukaryotic cytoskeleton is a network of filaments and tubules that extends from the nucleus to the plasma membrane that support cell shape and anchor organelles. ^•

Protein fibers Actin filaments ^– ^ cell movement ^– Intermediate filaments ^– Microtubules ^ centrioles ₆₀

Centrioles

^• Centrioles are short

cylinders with a 9 + 0 pattern of microtubule triplets. ^• Centrioles may be involved in microtubule formation and disassembly during cell division and in the organization of cilia and flagella. ₆₁

Cilia and Flagella

^•

_{Outer microtubule}

_Plasma

^•

_{0.1 µm}

_{Dynein arms}

_microtubule

_Central

_membrane

_Microtubules

_{proteins inside}

_{cross-linking}

_Radial

_{Basal body}

_membrane

_Plasma

_(b)

_(a)

_{0.1 µm}

_Triplet

(c) _{Cross section of basal body} ₆₂

Cilia and Flagella

^•

Cilia (small and numerous) and flagella (large and single)

have a 9 + 2 pattern of microtubules and are involved in

^•

basal

body

64 ^{(a) Motion of flagella. A flagellum} ^{usually undulates, its snakelike} ^{motion driving a cell in the same} ^{direction as the axis of the} ^{flagellum. Propulsion of a human} ^{sperm cell is an example of} ^{flagellatelocomotion (LM).} ^{Direction of swimming} ^{1 µm} Cilia and Flagella

(b) Motion of cilia. Cilia have a back- _{and-forth motion that moves the} _{cell in a direction perpendicular} _{to the axis of the cilium. A dense} nap of cilia, beating at a rate of _{about 40 to 60 strokes a second,} _{covers this Colpidium, a} _{freshwater protozoan (SEM).}

15 µm

Cell Structure and Function

Osmosis Osmosis

My definition of Osmosis My definition of Osmosis

Facilitated Diffusion Facilitated Diffusion

Endocytosis Endocytosis

Membrane Bound Organelles Nucleus 1 µm

Cytoskeleton

Centrioles

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Cell Structure and Function

Osmosis Osmosis

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Facilitated Diffusion Facilitated Diffusion

Endocytosis Endocytosis

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In this chapter I will learn to communicate states and events in progress, in order:

In this chapter I will learn to give an account of events and activites in order:

In this chapter I will learn how to write a short messages, and make a notices, in order: • to get what I want

We will learn to describe people, animals, and things in order: • to make them stand out

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