BIO 210 CHAPTER 3 STUDY GUIDE

Cell

is the basic structural and functional unit of living organisms/life.

three major regions of a generalized cell

Plasma Membrane
Cytoplasm
Nucleus

Plasma membrane

The outer boundary of the cell which acts as a selectively permeable barrier.

Cytoplasm

The intracellular fluid packed with organelles, small structures that perform specific cell function.

Nucleus

an organelle that controls cellular activities.

Plasma Membrane Composition

Lipid bilayer and proteins in constantly changing fluid mosaic

Plays dynamic role in cellular activity

Separates intracellular fluid (ICF) from extracellular fluid (ECF)

Interstitial fluid (IF) = ECF that surrounds cells

Plasma Membrane Lipids

75% phospholipids (lipid bilayer)
Phosphate heads: polar and hydrophilic
Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b)

5% glycolipids
Lipids with polar sugar groups on outer membrane surface

20% cholesterol
Increases membrane stability

Plasma Membrane Protein

Allow communication with environment

½ mass of plasma membrane

Most specialized membrane functions

Some float freely

Some tethered to intracellular structures

Two types of Plasma Membrane Proteins

Integral proteins and peripheral proteins

Integral Proteins

Firmly inserted into membrane (most are transmembrane)

Have hydrophobic and hydrophilic regions

Can interact with lipid tails and water

Function as transport proteins (channels and carriers), enzymes, or receptors

Peripheral proteins

Loosely attached to integral proteins

Include filaments on intracellular surface for membrane support

Function as enzymes

motor proteins for shape change during cell division and muscle contraction

cell-to-cell connections

Six Functions of Membrane Proteins

Transport

Receptors for signal transduction

Attachment to cytoskeleton and extracellular matrix

Enzymatic activity

Intercellular joining

Cell-cell recognition

The Glycocalyx

Sugar covering" at cell surface

Lipids and proteins with attached carbohydrates (sugar groups)

Every cell type has different pattern of sugars

Specific biological markers for cell to cell recognition

Allows immune system to recognize "self" and "non self"

Cancerous cells change it continuously

Cell Junctions

Some cells "free"
e.g., blood cells, sperm cells

Some bound into communities

Cell Junction: Three ways cells are bound

Tight junctions
Desmosomes
Gap junctions

Tight Junctions

Impermeable junctions
prevent molecules from passing through the intercellular space

Desmosomes

Anchoring junctions bind adjacent cells together like a molecular "Velcro" and help form an internal tension-reducing network of fibers.

Gap junctions

Communicating junctions
allow ions and small molecules to pass for intercellular communication.

Cells surrounded by interstitial fluid (IF) which

Contains thousands of substances, e.g., amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products

Plasma membrane allows cell to

Obtain from IF exactly what it needs, exactly when it is needed

Keep out what it does not need

Membrane transport

Plasma membranes selectively permeable

Some molecules pass through easily; some do not

Two ways substances cross membrane

passive processes and active processes

Passive Processes

No cellular energy (ATP) required

Substance moves down its concentration gradient

Active Processes

Energy (ATP) required

Occurs only in living cell membranes

Two types of Passive Transport

Diffusion and Filtration

Types Of Diffusion

Simple diffusion

Facilitated diffusion [Carrier-mediated or Channel-mediated]

Osmosis

Diffusion

Collisions cause molecules to move down or with their concentration gradient

Difference in concentration between two areas

Speed influenced by molecule size and temperature

Molecule will passively diffuse through membrane if

It is lipid soluble, or

Small enough to pass through membrane channels, or

Assisted by carrier molecule

Filtration

Usually across capillary walls

Simple Diffusion

Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer

E.g., oxygen, carbon dioxide, fat-soluble vitamins

Facilitated Diffusion

Certain lipophobic molecules (e.g., glucose, amino acids, and ions) transported passively by:

Binding to protein carriers

Moving through water-filled channels

Carrier-mediated Facilitated Diffusion

via protein carrier specific
for one chemical; binding of substrate causes transport protein to change shape

Channel-mediated Facilitated Diffusion

through a channel
protein; mostly ions
selected on basis of
size and charge

Osmosis

Movement of solvent (e.g., water) across selectively permeable membrane

Osmosis: Water diffuses through plasma membranes through ____________

Through lipid bilayer

Through specific water channels called aquaporins (AQPs)

Osmosis occurs when water concentration is ________ on the two sides of the membrane

Different

Osmosis

Membrane permeable to both solutes and water

Membrane permeable to water, impermeable to solutes

Importance of Osmosis

Osmosis causes cells to swell and shrink

Change in cell volume disrupts cell function, especially in neurons

Two types of Active Processes

Active transport and vesicular transport

Active transport

Requires carrier proteins (solute pumps)

Bind specifically and reversibly with substance

Moves solutes against concentration gradient
Requires energy

Two types of active transport

Primary and secondary

Primary active transport

Required energy directly from ATP hydrolysis

Secondary active transport

Required energy indirectly from ionic gradients created by primary active transport

Depends on ion gradient created by primary active transport

Energy stored in ionic gradients used indirectly to drive transport of other solutes

Most investigated example of primary active transport

Sodium-potassium pump

Carrier (pump) called Na+-K+ ATPase

Located in all plasma membranes

Involved in primary and secondary active transport of nutrients and ions

Cotransport

always transports more than one substance at a time

Symport system

Substances transported in same direction

Antiport system

Substances transported in opposite directions

Vesicular transport

Transport of large particles, macromolecules, and fluids across membrane in membranous sacs called vesicles

Requires cellular energy (e.g., ATP)

Exocytosis

transport out of cell

Endocytosis

Transport into cell

Three types of endocytosis

Phagocytosis
pinocytosis
receptor-mediated

Phagocytosis

Pseudopods engulf solids and bring them into cell's interior

Form vesicle called phagosome

Used by macrophages and some white blood cells

Pinocytosis [fluid-phase]

The cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated

Receptor-mediated

Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles.

Exocytosis

Usually activated by cell-surface signal or change in membrane voltage

Substance enclosed in secretory vesicle

v-SNAREs ("v" = vesicle) on vesicle findt-SNAREs ("t" = target) on membrane and bind

Functions of exocytosis

Hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes

Exocytosis

Resting membrane potential - how it is established

Diffusion causes ionic imbalances that polarize the membrane, and active transport processes maintain that membrane potential

Cell-Environment Interactions always involve

glycocalyx

Cell adhesion molecules (CAMs)

Plasma membrane receptors

Voltage-gated channel proteins

Roles of Cell Adhesion Molecules

Attract WBCs to injured or infected areas

Stimulate synthesis or degradation of adhesive membrane junctions

Transmit intracellular signals to direct cell migration, proliferation, and specialization

Contact signaling

touching and recognition of cells; e.g., in normal development and immunity

Chemical signaling

interaction between receptors and ligands (neurotransmitters, hormones, and paracrines) to alter activity of cell proteins (e.g., enzymes or chemically gated ion channels)

Chemical signaling diagram

Composition of cytosol

Located between plasma membrane and nucleus

Composed of:
Cytosol
Organelles
Inclusions

Cytosol

Water with solutes (protein, salts, sugars, etc.)

Organelles

Metabolic machinery of cell; each with specialized function; either membranous or nonmembranous

Inclusions

Vary with cell type; e.g., glycogen granules, pigments, lipid droplets, vacuoles, crystals

Mitochondria

Double-membrane structure with inner shelflike cristae

Contain their own DNA, RNA, ribosomes

Mitochondria provide most

of cell's ATP via aerobic cellular respiration

Requires oxygen

Mitochondria is similar to bacteria because it is capable of cell division called

fission

Mitochondrion

Ribosome

Granules containing protein and rRNA

Site of protein synthesis

Free ribosomes

synthesize soluble proteins that function in cytosol or other organelles

Membrane-bound ribosomes

(forming rough ER) synthesize proteins to be incorporated into membranes, lysosomes, or exported from cell

Endoplasmic Reticulum (ER)

Interconnected tubes and parallel membranes enclosing cisterns

Continuous with outer nuclear membrane

Two varieties of ER

Rough ER and Smooth ER

Rough ER

External surface studded with ribosomes

Manufactures all secreted proteins

Rough ER synthesizes membrane integral _____ and ______

proteins and phospholipids

Smooth ER

Network of tubules continuous with rough ER

The enzymes of Smooth ER function in

Lipid metabolism; cholesterol and steroid-based hormone synthesis; making lipids of lipoproteins

Absorption, synthesis, and transport of fats

Detoxification of drugs, some pesticides, carcinogenic chemicals

Converting glycogen to free glucose

Storage and release of calcium

Golgi apparatus

Stacked and flattened membranous sacs

The golgi apparatus modifie, concentrates, and packages proteins and lipids from the _______ __

Rough ER

Golgi apparatus diagram

Peroxisomes

Membranous sacs containing powerful oxidases and catalases

Peroxisomes detoxify harmful or toxic substances and

Catalysis and synthesis of fatty acids

Peroxisomes neutralize dangerous

free radicals (highly reactive chemicals with unpaired electrons)

Lysosomes are

Spherical membranous bags containing digestive enzymes (acid hydrolases)

"Safe" sites for intracellular digestion

Lysosomes digest ingested bacteria, viruses, and toxins as well as

Degrade nonfunctional organelles

Lysosomes

Destroy cells in injured or nonuseful tissue (autolysis)

Break down bone to release Ca2+

Cytoskeleton

Elaborate series of rods throughout cytosol; proteins link rods to other cell structures

Three types fibers that make up the cytoskeleton

Microfilaments

Intermediate filaments

Microtubules

Microfilaments

Thinnest of cytoskeletal elements

Dynamic strands of protein actin

Each cell has a unique arrangement of strands

Microfilaments are involved in cell motility, change in shape, endocytosis and ____________

exocytosis

Microfilaments diagram

Intermediate filaments

Tough, insoluble, ropelike protein fibers

Composed of tetramer fibrils

Resist pulling forces on cell; attach to desmosomes

Intermediate Filaments diagram

Microtubules

Largest of cytoskeletal elements; dynamic hollow tubes; most radiate from centrosome

Microtubules determine overall shape of the cell and distribution of _______

organelles