Cells Chapter 3. Cellular Basis of Life Structural units of all living things Human adult has around...
-
Upload
maximilian-dorsey -
Category
Documents
-
view
225 -
download
0
Transcript of Cells Chapter 3. Cellular Basis of Life Structural units of all living things Human adult has around...
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.
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 3.8f
Processes
Rough ERNerve cell
Nucleus
(f) Cell that gathers information and controls body functions
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
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
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)