CH. 3 Structure and Function of Cells
Cell Doctrine
All living things are composed of cells
A single cell is the smallest unit that exhibits all the characteristics of life.
All cells come only from pre-existing
cells Two Basic Cells
Prokaryotic Cells
oOnly bacteria & blue-green algae
oPlasma membrane
oNo nuclear membrane
oCytoplasm: fluid within membrane
oOnly ribosomes (no organelles)
oSmaller than Eukaryotic cells
Eukaryotic Cells
oPlasma membrane
oNucleus: information center & nuclear membrane
oCytoplasm
oOrganelles: structures with specialized functions
oAll human cells
Cell Structure Reflects Cell Function
Though eukaryotic cells are remarkably similar there are structural differences
Ex: muscle cells
oContain numerous organelles providing energy needed for muscle contraction
Ex: nerve cells
oLong and thin to carry impulses over distance
Small size is efficient
Cells Remain Small to Stay Efficient
Small cells have higher surface:volume ratio
High surface:volume ratio promotes efficiency in:
oAcquisition of nutrients
oDisposal of wastes
Plasma Membrane Surrounds Cell
Separates a cell from its environment
Selectively permeable
oPermits movement of some substances into & out of the cell, but blocks others
Enables transfer of information between environment and cell
Plasma membrane is a lipid bi-layer
oPhospholipids: polar head & non-polar tails
oCholesterol: makes membrane a bit more rigid & helps maintain
certain/particular proteins in particular places and keeps them from migrating.
oProteins: provide means of transport through membrane
oCarbohydrates: recognition patterns for cells and organisms
oNon rigid
oFluid mosaic
Molecules Cross the Plasma Membrane in Several Ways
Passive Transport
oCell does not have to expand energy for this
▪Diffusion- Movement of molecules or atoms from higher region/level
of concentration to lower region/level of concentration.
▪Osmosis- Diffusion of water
Active Transport
oCell must expend energy (ATP) (need protein too) & moving material from
higher region/level of concentration to lower region/level of concentration.
Bulk Transport
oInvolves membranous vesicles to move larger substances
▪Endocytosis- Obtaining many molecules
▪Exocytosis- Getting rid of many molecules
Passive Transport with Concentration Gradient
Passive transport is powered by concentration gradient in the cell occurs as:
oDiffusion through lipid layer
oDiffusion through protein channels (water goes through protein channel)
oFacilitated transport
▪Transport or carrier proteins in the membrane assist in moving molecules
across the membrane, down the concentration gradient, without expending
energy.
Active Transport
oActive transport moves substances from an area of lower concentration to an
area of higher concentration.
▪Requires a membrane protein (transporter)
▪Requires ATP or other energy
source Endocytosis & Exocytosis Move Materials in Bulk
Used to move larger molecules
oEndocytosis- brings substances into cells
oExocytosis- expels substances from cells
Information Transfer Across the Plasma Membrane
Receptor proteins span membrane- required for transmission of information to &
from cell.
Receptor sites (on receptor proteins)- interact specifically with signal molecules
A change is triggered within the cell as a result of binding of signal molecules to receptor
site.
Different cell types have different receptor proteins
The Sodium-Potassium Pump: Helps Maintain Cell
Volume
Sodium-Potassium pump expels unwanted ions, keeps needed ones, and maintains
cell volume.
ATP is used to expel 3 sodium ions for every 2 potassium ions brought into the cell
Increase in cell volume = increase in water in cytoplasm by decreasing pumping and
allows more sodium inside cell.
Decrease in cell volume = less water in cytoplasm by increasing pumping and expelling
more sodium ions
Isotonic Extracellular Fluid Maintains Cell Volume
Tonicity
oExtracellular & intracellular ionic concentrations are equal
oCells maintain a normal volume in isotonic extracellular fluids
oRegulatory mechanisms maintain extracellular fluid that is isotonic with
intracellular fluid
oCell will always remain the same size (concentration is the same/volume is
constant).
Variations of Tonicity
oHypertonic
▪Extracellular ionic concentration higher than intracellular ionic
concentration
▪Water will diffuse out of cell
▪Cell will shrink and die (crenate-another word for shrink)
oHypotonic
▪Extracellular ionic concentration lower than intracellular ionic
concentration
▪Water will diffuse into the cell
▪Cell may swell and burst (plasmolyze- swelling & bursting of cytoplasm)
Inside a Cell
Nucleus
oFunction
▪Contains the genetic information of the cell
▪Controls the cell
oStructural Features
▪Double-layered nuclear membrane
▪Nuclear pores (57 different proteins needed)
▪Chromosomes/chromatin
▪Nucleolus (a piece of DNA that codes for a special structure called
a ribosome)
oRibosomes
▪Site of protein synthesis
▪Location
Free: floating in cytoplasm
Bound: attached to outer surface of endplasmic reticulum
Endoplasmic Reticulum
Two types of Endoplasmic Reticulum
oRough ER
▪Has ribosomes on surface
▪Protein manufacturing, modifications
oSmooth ER
▪No ribosomes on surface
Golgi Apparatus
▪Lipid synthesis
▪Packages the proteins
Refines synthesized products
Packaging & shipping order
Products are packaged into vesicles and shipped to other locations within the cell or
to the cell membrane for export.
Vesicles
Storage and shipping vesicles
Secretory vesicles
Endocytic vesicles
Peroxisomes
oContain enzymes detoxify
Lysosomes
oContain digestive enzymes
oUse this in the immune system
oDevelop natally/ mentally
Mitochondria
“Power plant” of the cell
Surrounded by a double membrane
Utilizes O2 and produces CO2 and water vapor
Generates ATP
Fat and Glycogen: Sources of Energy
Fat
oTriglycerides
oLong-term energy storage in animals
Glycogen
oCarbohydrates
oShort-term energy storage in
animals Cell Structure for Support and Movement
Cytoskeleton
oMicrotubes
oMicrofilaments
oIntermediate filaments
Cilia
oShort, many
oFound on cells lining airways
Flagella
oLong, simple
oEnable spermatozoa to swim
Centrioles
Cells use and Transform Matter & Energy
Metabolism: all the chemical reactions that go on in a cell
Anabolism
oRequires enzymes
oUsed in making/assembling cell compounds
oUsed in storing energy
Catabolism
oRequires enzymes
oBreakdown of molecules
oReleases energy
oUsed in breaking down nutrients & recycling all compounds
oUsed to access energy
storage Glucose Provides Cell with Energy
Glucose provides energy for cell
Energy in glucose is used to generate ATP
In absence of glucose other carbohydrates, fats and protein can be catabolized to
generate ATP
Four Stages of Cellular Respiration
Glycolysis
oTakes place in cytoplasm
oDoes NOT require oxygen
oAnaerobic
o2 ATP are producded (net)
o4 ATP (gross) but cost 2 (net amount above)
Citric acid cycle
oOccurs in mitochondria
oKrebs cycle
oProduces 2 ATP & carbon dioxide (as a waste product)
Electron Transport System (ETS)
oLocated in inner mitochondrial membrane
oOxygen is required
oProcess is known as oxyidative phosphorylation
oGenerates a ton of ATP
oATP generated from ATP synthase enzyme
o32 ATP are made
Additional Energy Sources
oGlycogen
oFats
▪Triglycerides have twice the energy of carbohydrates
oProteins
▪Same energy as carbohydrates
