HAN 200 Cellular form & function

Cell Theory

• All living organisms are made of one or more

  cells.

  •The cell is the smallest structural and

  functional living unit

  •Biochemical activities of cells are dictated by

  their specific subcellular structures

  •Continuity of life has a cellular basis, all cells

  arise from preexisting cells.

Plasma Membrane

Flexible outer boundary, selectively permeable

Cytoplasm

Intracellular fluid containing organelles

Located between plasma membrane and nucleus

• 1. Cytosol (properties of a colloid)

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

• 2. Cytoplasmic organelles

• Metabolic machinery of cell

• 3. Inclusions (chemical substances)

• Granules of glycogen or pigments, lipid droplets, vacuoles, and crystals

Nucleus

Control center

Organelles

Structures in the cell that perform various tasks

Cell Membrane

75% phospholipids (lipid

bilayer)

• Phosphate heads: polar and hydrophilic

• Fatty acid tails: nonpolar and hydrophobic

• 5% glycolipids (carbohydrates)

• Lipids with polar sugar groups on outer membrane surface

• 20% cholesterol

• Increases membrane stability and fluidity

Transmembrane Proteins (integral proteins)

two types of membrane proteins

• Firmly inserted into the membrane, protrude on both sides

• Functions as transport proteins (channels & carriers), enzymes or receptors

Peripheral proteins

2 types of membrane proteins

• Loosely attached to integral proteins

• Functions as enzymes, motor proteins, cell to cell links, provide support on intracellular surface & form part of glycocalyx

Microvilli

• Fingerlike extensions of plasma membrane

  • Increase surface area for absorption

  • Core of actin filaments for stiffening

  • Seen in absorption in the digestive tract

Cilia & Flagella

Whiplike, motile extensions on surfaces of certain cells

• Contain microtubules and motor molecules

• Cilia move substances across cell surfaces

• Longer flagella propel whole cells

Passive Transport

No energy required, substance move down concentration gradient

Active Transport

energy required (ATP)

Filtration

Type of Passive Process:

Particles are driven through membrane by physical pressure (coffee filter)

Simple diffusion

Type of passive process

Net movement of particles from place of high concentration to place of lower concentration

Osmosis

type of passive process

Movement of solvent (water) across a selectively permeable membrane

Isotonic

A solution with the same solute concentratTion as that of the cytosol

Tonicity

The ability of a solution to cause a cell to shrink or swell

Hypotonic

A solution having lesser solute concentration that that of the cytosol

Hypertonic

A solution having greater solute concentration than that of the cytosol

Carrier-mediated transport

proteins (carriers) in cell membrane carry solutes into or out of cell (or organelle)

• Carriers exhibit specificity for their particular solutes

• Solute (ligand) binds to receptor site on carrier protein

• Solute is released unchanged on other side of membrane

• Carriers also exhibit saturation

• As solute concentration rises, the rate of transport rises, but only to a point called the transport maximum

Facilitated Diffusion

three types of carrier-mediated transport

carrier moves solute down its concentration gradient

• Does not consume ATP; passive transport

• Solute attaches to binding site on carrier, carrier changes conformation, then releases solute on other side of membrane

Primary Active Transport

three types of carried-mediated transport

carrier moves solute through a membrane up its concentration gradient

Secondary active transport

Three types of carrier-mediated transport

carrier moves solute through membrane, but only uses ATP indirectly.

Sodium-Potassium Pump

Pumps Na and K against their concentration gradient, therefore, needs energy. Cells have a higher concentration of K+ in the cell and higher concentration of Na+ outside of the cell.

Pumps 3 Na out of the cell and 2 K into the cell.

Vesicular Transport

Transport of large particles, macromolecules, and fluids across plasma membrane

Endocytosis

Transport into cell

-phagocytosis, pinocytosis, receptor-mediated endocytosis

exocytosis

Transport out of cell

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

Transcytosis

Transport into, across, and then out of cell

Phagocytosis

In endocytosis

The cell engulfs a large particle by forming projecting pseudopods (“false feet”) around it and enclosing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle or are ejected by exocytosis.

Pinocytosis

The cell “gulps” drops of extracellular fluid containing

solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated. ex: nutrient absorption in the small intestine

Receptor mediated endocytosis

clathrin-coated pits provide main route for endocytosis and transcytosis

• A more selective form of endocytosis, requires a specific receptor to allow the cell to ingest

• Uptake of enzymes, hormones, low-density lipoproteins, iron, and insulin

• macromolecules

Mitochondria

Double-membrane structure with shelflike cristae

provide most of cell’s ATP via aerobic cellular respiration (powerhouse of cell)

contain their own DNA and RNA (can reproduce themselves)

Ribosomes

Granules containing protein and rRNA

•Site of protein synthesis, assembles AA

•Free ribosomes synthesize soluble proteins for use within the cell

•Membrane-bound ribosomes (on rough ER) synthesize proteins to be incorporated into membranes or exported from the cell

Endoplasmic Reticulum (ER)

“highway system”

Interconnected tubes

•Continuous with nuclear membrane

•Two varieties:

• Rough ER (have ribosomes attached)

• Smooth ER

Rough ER

External surface studded with ribosomes

•Manufactures all secreted proteins

•Synthesizes membrane integral proteins and phospholipids (“membrane factory”)

Smooth ER

(no role in protein synthesis)

Synthesis of:

- phospholipids and cholesterol

- steroid hormones

• Synthesis & storage of:

- glycerides

- glycogen

- calcium (skeletal MM)

Golgi Apparatus

Stacked and flattened membranous sacs

• Transport vessels from ER fuse with receiving end of Golgi apparatus

• Three types of packaged products leave

Golgi:

1. plasma membrane renewal

2. secretions to be discharged from cell

3. become secretory vesicles or lysosome that store a cell product. Ex: breast milk or enzymes

Lysosomes

Membraneous bags containing digestive enzymes

• Digest ingested bacteria, viruses, and toxins

• Degrade nonfunctional organelles

• Break down and release glycogen

• Break down bone to release Ca2+

• Destroy cells in injured or nonuseful tissue (autolysis) webbed fingers and toes in fetus

• Can cause programmed cell death

Peroxisomes

Membranous sacs containing powerful oxidases; resemble lysosomes but contain different enzymes.

•Detoxify harmful or toxic substances (alcohol and free radicals)

•Numerous in liver and kidney

•Catabolizes fats

•Smaller than lysosomes

Microfilaments

Cell mobility, actin strands (microvilli)

Intermediate Filaments

Tensile Strength

Microtubules

Hollow tubes, moves chromosomes during cell division

Centrosome

“Cell center” near nucleus

•Generates microtubules; organizes mitotic spindle for cell division.

•Contains paired centrioles: Small tube formed by microtubules

Nucleus

“brain of the cell”

Genetic library with blueprints for nearly all cellular proteins

•Responds to signals and dictates kinds and amounts of proteins to be synthesized

•Most cells are uninucleate

•Red blood cells are anucleate – short life span

•Skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate – due to large cytoplasm area to be regulated

Nucleoli

Dark-staining spherical bodies within nucleus

• Involved in rRNA synthesis and ribosome subunit assembly

• “little nuclei”

Chromatin

Threadlike strands of DNA

•Arranged in fundamental units called nucleosomes

•Condense into bar-like bodies called chromosomes when the cell starts to divide

• This allows for tight packing of DNA material in a small space