Cells Chapter 3. Cellular Basis of Life Structural units of all living things Human adult has around 75 trillion cells Cells are 60% water, and bathed.

Cells

Chapter 3

Cellular Basis of Life• Structural units of all living things• Human adult has around 75 trillion

cells• Cells are 60% water, and bathed in

a dilute saltwater solution (interstitial fluid)

• Cell Theory– Cell is the basic structural and

functional unit of living organisms– Activity of an organism depends on

activities of cells– Biochemical activities of cells are

dictated by the relative number of their subcellular structures

– Continuity of life has a cellular basis

Cell Properties = Properties of Life!

Anatomy of a Generalized Cell

• Cells are not all the same!• Generalized cell –

demonstrates functions common to all cells– All cells have three main regions:Nucleus

Cytoplasm

Cell membra

ne

Cell Nucleus• “headquarters” or control center of

cell• Contains DNA

– Instructions for building proteins– Necessary for cell reproduction

• Conforms to shape of cell• Three regions/structures

– nuclear envelope (double layer)– nucleolus (nucleoli)

• RNA + protein• site of ribosome production

– Chromatin (DNA + protein)• Form chromosomes

Fluid Mosaic Model

Plasma Membrane• Selectively permeable• Composed of lipids, proteins, and

carbohydrates in a phospholipid bilayer

Plasma Membrane• Phospholipids

– heads = hydrophilic, tails = hydrophobic

– O2 & CO2 can pass through easily, others cannot

• Impermeable to water soluble molecules

• Cholesterol embedded in the bilayer – helps with structural stability

LINK

Plasma Membrane• Proteins have many functions!

– Receptor proteins • Receive hormones/chemical

messengers– Form pores

• Water & water soluble molecules to pass through

– Selective channels• Transport specific ions

– Glycoproteins form recognition sites (marker)• Cell identification!• Glycocalyx: sticky surface of cell

due to sugars

Membrane Junctions• Some cells loose in body (blood cells,

sperm, phagocytic cells)• Cells bound together in three ways:

– Glycoproteins in glycocalyx act as adhesive

– Wavy contours of membranes of adjacent cells fit in tongue-and-groove fashion

– Special membrane junctions are formed (vary structurally depending on function!)• Tight: impermeable, leakproof,

prevent substances from passing through (like a zipper)

• Desmosomes: anchoring junctions (like rivets), prevents cells from being pulled apart

• Gap junctions: allow communication

Cytoplasm• Cellular material outside the

nucleus and inside the plasma membrane

• “factory area” where cellular activity takes place

• 3 elements:– Cytosol (fluid that suspends

elements)– Organelles (metabolic machinery of

cell)– Inclusions (chemical substances

present based on the different type of cell)• i.e. lipid droplets in fat cells,

glycogen granules in liver/muscle cells, pigments in hair & skin cells, mucus, etc.

Pg. 68-71

Cell ExtensionsCilia Flagella

Cell DiversitySTRUCTURE DETERMINES

FUNCTION• Over 200 different cell types in

the human body• Cells differentiate in

development• Vary in size, shape, and function

Cell Diversity

Figure 3.8a

FibroblastsRough ER and Golgiapparatus

No organelles

NucleusErythrocytes

(a) Cells that connect body parts

Cell DiversityEpithelialcells

Nucleus

Intermediatefilaments

(b) Cells that cover and line body organs

Figure 3.8b

Cell DiversitySkeletalmuscle cell

Nuclei Contractile

filaments

Smoothmuscle cells (c) Cells that move organs and body parts

Figure 3.8c

Cell Diversity

Figure 3.8d

Fat cell Lipid droplet

(d) Cell that stores nutrients

Nucleus

Cell DiversityLysosomesMacrophage

(e) Cell that fights disease

Pseudopods

Figure 3.8e

Cell Diversity

Figure 3.8f

Processes

Rough ERNerve cell

Nucleus

(f) Cell that gathers information and controls body functions

Cell Diversity

NucleusFlagellum

Sperm

(g) Cell of reproduction

Figure 3.8g

Cell Physiology: Membrane Transport

• Movement of substances into and out of the cell

• Cell membranes are selectively permeable– Some substances can pass through but

others cannot (only healthy/unharmed cells!)

– Due to phospholipid bilayer• Two basic methods of transport:

– Passive process (no energy required)– Active processes (cell must provide

metabolic energy (ATP)

ATP

Membrane Transport• Passive mechanisms

– Simple diffusion– Osmosis– Facilitated diffusion– Filtration

• Active mechanisms– Active transport (solute pumping)– Vesicular transport

• Exocytosis• Endocytosis

Passive Transport: Diffusion• Molecules and ions move away

from a region where they are more concentrated to a region where they are less concentrated– Concentration gradient (rate

affected by differences in concentration)

– Powered by kinetic energy (rate of diffusion affected by size of particles & temperature)

• Phospholipids control diffusion through membrane. Molecules diffuse if:– Small enough to pass through pores

formed by proteins (simple)– Lipid soluble (simple)– Assisted by a membrane carrier

Passive Transport: Diffusion

• Simple diffusion: unassisted diffusion of solutes through a selectively permeable membrane– Lipid-soluble (fats, fat-soluble

vitamins, O2, CO2)– Pass through membrane pores

(small ions such as Cl-)• Osmosis: diffusion of water

through selectively permeable membrane – Passes through aquaporins protein

(channels)

Cytoplasm

(a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer

Extracellular fluid

Lipid-solublesolutes

(d) Osmosis, diffusion of water through a specific channel protein (aquaporin) or through the lipid bilayer

Watermolecules

Lipidbilayer

Osmosis

Passive Transport: Diffusion• Facilitated diffusion

– Passage of lipid-insoluble and large molecules (i.e. glucose)

– Uses protein carriers or channels– Down concentration gradient

• Filtration– Water and solutes forced through a

membrane (or capillary wall) by fluid (hydrostatic) pressure

– Move down pressure gradient– Solute-containing fluid (filtrate)– Not selective (blood cells & proteins

too large)– i.e. kidneys

Active Transport• Cell uses ATP supply to move

substances across the membrane– Substances too large for channels,

membrane lacks protein carriers for them, not lipid-soluble, or against concentration gradient

• Solute pumping (active transport) : require protein carriers (solute pumps powered by ATP) – Very specific– Amino acids, most ions, some

sugars, sodium-potassium pump

Active Transport: Vesicular Transport

• Uses ATP to move substances into or out of cells without their actually crossing the plasma membrane

• Exocytosis: moves substances out of cell– Secrete hormones, mucus, and other cell

products or eject cellular wastes (i.e. secretory cells, nerve cells)

– Packaged in golgi into a vesicle• Endocytosis: moves substances into

cell– Engulf extracellular substances by

enclosing them in small vesicle, digested by lysosomes

– Phagocytosis: use pseudopods (phagocytes) – protective mechanism (i.e. macrophages, neutrophils)

– Pinocytosis: cell “gulps” droplets of ECF (absorption, i.e. small intestine)

Phagocytosis

Exocytosis

Endocytosis

Cell Cycle• Series of changes a cell goes

through from the time it is formed until it divides

• Two periods:– Interphase (“living”): cell grows &

carries on usual metabolic activities• DNA replication occurs (S phase)

– Cell division: reproduction of the cell

Cell Division

• Mitosis– Prophase– Metaphase– Anaphase– Telophase

• Cytokinesis– Division of cytoplasm– Liver (binucleate and

multinucleate cells due to no cytokinesis)

Cell Differentiation

• Process by which cells develop different characteristics in structure & function

• 200 different cell types!