Chapter 3 THE CELLULAR LEVEL OF ORGANIZATION

I. Cell

A.basic structural and functional unit of life

B.trillions of cells in the human body

C.activity of an organ depends on individual cellular functions as well as collective

functions of cells (tissue)

D.Size

1.average 10 microns

2.RBC is 4 microns and goes through a 5 micron capillary

3.various shapes

a.oval - RBC

b.elongated - skeletal muscle 30cm

c.1 meter - nerve

E.The structure of a cell determines its functions

F.Composed of:

1.cell membrane

2.cytoplasm - intracellular (inside the cell)

3.organelles - intracellular tiny organs each with a specific function

II.Plasma membrane

A.Composition

1.Phospholipid bilayer

a.phosphate groups (head) face the outside of the cell (extracellular) and towards the inside of the cell (intracellular)

b.lipid tails face each other in the bilayer

c.not two membranes

d.hydrophobic region is nonpolar - lipid tails

e.hydrophilic region is polar - phosphate heads

f.allows for compartmentalization

g.same membrane structure found on organelles

2.Proteins

a.integral

(1)within the bilayer

(2)many form channels across

(3)form cell surface receptors for substances to bind to for cell response

b.peripheral

(1)along inside edge of the membrane

3.Cholesterol

a.helps stabilize membrane

b.lipids and cholesterol determine the temperature at which the

membrane fluidity is retaine (Don't want it rigid or too liquid)

c.fat soluble molecule

4.Fluid Mosaic Model of the Plasma Membrane

a.mosaic is a pattern

b.the proteins form a pattern in the phospholipids

c.fluid refers to the molecules moving within the

bilayer (laterally)

5.Glycocalyx

a.branched sugar groups on extracellular surface

6.Microvilli

a.extensions of plasma membrane

b.increases surface area of the cell

c.important on cells in the small intestine to absorb nutrients from diet

7.Desmosomes

a.connections between adjacent cells

(bottom of cells sit on a basement membrane)

b.forms a junction to anchor

(1)tight- limits what can move between cells

(2)gap - places for molecules to pass

(3)important in arrangement of membranes and other tissues

8.DRAW THE PLASMA MEMBRANE

B.Transport

1.Movemement of substances between the extracellular fluid and intracellular

2.Extracellular fluid = interstitial fluid in tissues

a.made from blood and is similar to plasma

b.delivers nutrients, oxygen

c.removes wastes, carbon dioxide

3.Most membranes are selectively permeable

a.certain things pass, others do not

b.permeable implies everything passes

c.impermeable - nothing passes

4.Passive Processes

a.no energy required

b.types

(1)simple diffusion

(a)down a concentration gradient

(b)rate influenced by

i)size

ii)charge

iii)temperature

(c)molecule diffuses until reaches equilibrium (same concentration on both sides of the membrane)

(2)osmosis

(a)refers to water movement

(b)water moves from area where solute is in a low concentration (water is high concentration) to area where solute is in a high concentration (low concentration of water).

(c)water moves to dilute a solute until equilibrium occurs

(3)facilitated diffusion

(a)cannot cross the plasma membrane

(b)requires a carrier (Protein)

(c)still moves down its concentration gradient

(4)filtration

(a)forces substances across by changing pressure

(b)hydrostatic pressure

i)pressure exerted by a column of water (or blood in the body)

ii) osmotic pressure opposes hydrostatic pressure

(5)A cell requires a constant concentration of solutes in its environment (interstitial fluid). If this concentration changes the cell will respond. Normal saline has the same salt concentration as plasma or interstitial fluid (0.9% NaCl). Cells outside the body will not change if placed in this isotonic saline solution. If the concentration of NaCl is more (hypertonic), it will exert more pressure on the cell. This is a sucking force to pull water out of the cell. The volume of the cell will decrease and the cell will shrink. On the other hand if the solution is less salt (hypotonic solution) the inside of the cell will have more solutes and suck water into the cell. The cell will then increase in size until the concentration is equal or burst. Water is moving by OSMOSIS. The salt does not initially move.

c.Active Processes

(1)require energy in the form of ATP

(2)move substances up their concentration gradients or from low to high

(3)require a carrier

(a)many carriers transport two substances

i)symport in same direction

a)both in or both out

ii)antiport in opposite direction

a)one in cell the other out

b)40% of a cell's energy is used in active transport

(b)Na/K ATPase moves 3 Na out and 2 K in

(c)some transport without directly using ATP but use the energy of the ion gradient (Na+) in secondary active transport (Ca, H, Glucose, amino acid)

(4)vesicular transport

(a)exocytosis

i)secretion of a substance from a cell (like mucus, hormones)

ii)breaks off part of the plasma membrane

(b)endocytosis

i)takes substances into cells

ii)phagocytosis

a)cell eating

b)Ex. WBC eats bacteria

iii)pinocytosis

a)cell drinking

b)substance is liquid

C.Resting Membrane Potential

1.All cells have a potential across the membrane.

a.-20 to -200 mv.

2.This is a current due to differences in ion concentrations on each side.

3.Na⁺ is the major extracellular ion.

4.K⁺ is the major intracellular ion.

5.Resting membrane potential of most cells due to a diffusion of these two ions. All other charges are balanced. The membrane is more permeable to K⁺ which wants to move out of the cell or down its concentration gradient. Although Na really wants to move inside the cell at the same rate it cannot because the membrane is less permeable to Na. Remember that both have positive charges. As K moves out more + charges are outside than inside the cell so the cell is said to have a NEGATIVE CHARGE inside relative to the outside. This gradient is across the membrane and the movement of + ions (cations) inside the cell will make the potential more positive and moving the + ions outside will make it more negative. The Na/K ATPase pump helps maintain the potential.

6.The cell is said to be polarized.

7.Excitable cells can change the potential by making Na and K move across the membrane - depolarize and repolarize the membrane. Nervous impulse, muscle contraction

D.Cytoplasm

1.Material inside plasma membrane

2.site where many cellular activities take place

3.between plasma membrane and nucleus

4.contains:

a.cytosol - viscous, semitransparent fluid; excludes organelles

b.organelles - tiny organs

c.inclusions - deposits of substances

d.cytoplasm often used when really referring to the cytosol - it originally referred to all that could not be seen under the microscope (Electron microscope used to see other components)

III.Organelles

A. Cytoskeleton

1.network of protein structure

2.support of cell

3.microfilaments

a.actin

b.attaches to plasma membrane

4.microtubules

a.tubulins

b.long tubes

5.intermediate filaments

a.tough

b.stabilize

6.gel of cytosol is a microtrabecular lattice (spider web)

B.Centrosome

1.Microtubule organizing center MOC

2.location of the centrioles

3.role in cell division

C.Projections from cell

1.cilia

a.short hair like

b.move substances along cell surface

2.flagella

a.longer than cilia

b.sperm have 1 flagella to propel

D.Ribosomes

1.made of proteins and rRNA (ribosomal RNA from nucleolus)

2.composed of a small and large subunit

3.reads mRNA (messenger RNA)

4.is the site where amino acids join in peptide bonds to make a protein

5.in cytoplasm as free ribosomes

6.on the surface of rough endoplasmic reticulum

E.Endoplasmic reticulum

1.coiled membrane with fluid filled cavities

2.RER

c.ribosomes on surface

d.modifies proteins after they are made by ribosomes

e.Carbohydrate added as protein enters ER

f.protein travels through changes are made by

enzymes present in the RER

3.SER

a.smooth or without ribosomes

b.storage of certain molecules (calcium)

c.synthesis of some molecules (lipids)

F.Golgi complex (apparatus)

1.modify and packages and tags proteins

2.cisternae : sacs that contain certain enzymes act on the entering protein from the RER

a.remove groups

b.add groups

c.examples

(1) glycoproteins - enters RER and golgi may cut and trim carbohydrates

(2)may add phosphate groups

3.protein leaves RER by pinching off part of membrane

4.fuses with Golgi membrane

5.passes from one sac to next

6.Tags protein for its destination

a.plasma membrane

b.secretion

c.lysosome

G.Lysosome

1.membranous sac containing hydrolytic enzymes

a.hydrolysis (digest)

2.More in phagocytes

a.WBC

3.Digestive enzymes work at a specific pH

4.Particles entering cell by endocytosis have part of plasma membrane around it and then fuses with membrane of lysosome

5.has to be separated to prevent digestion of cell

6.digests worn out cell parts

H.Peroxisomes

1.membranous sacs with enzymes

2.attacks oxygen free radicals

a.very reactive molecule that looks for molecules to react with (DNA and proteins are attractive) and can cause cell damage

I. Proteosomes

1. continuous destruction of proteins

J. Mitochondria

3.Powerhouse of the cell

b.most ATP is made here

4.Double membrane

a.cristae

(1)folds on inner membrane to increase surface area

(2)enzymes found here for chemical reactions

5.Has its own DNA and RNA to replicate when more mitochondria are needed

IV.Nucleus

A.Largest organelle within the cell

1.Control center of cell

a.with genetic information

2.most cells have one

a.some multinucleated

b.anucleated

(1)mature RBC

(2)will die

3.generally centrally located

4.

B.Composition

1.Nuclear envelope or membrane

a.double layer

b.perinuclear cisterna

(1)perinuclear fluid fills space between two membranes

c.nuclear pores at fusion of 2 membranes

d.continous with ER

2.Nucleoplasm

a.gel fluid filling nucleus

3.nucleoli

a.bodies within the nucleus

b.produces ribosome (rRNA)

(1)ribosomal subunits leave via pores to cytoplasm and are then joined together

4.chromatin

a.DNA and histones

b.DNA is genetic material

c. segments of DNA in genes that code for proteins (35,000-45,000 human genes)

c.histones

(1)globular proteins

(2)DNA coiled around (beads on a string)

d.nucleosome

(1)fundamental units of chromosome

(2)8 histones by DNA strand

(3)must uncoil to expose DNA for replication or protein synthesis

V.Protein Synthesis

1.DNA contains genes for making proteins

2.sequence of 3 nucleotide bases gives a code for each amino acid - codon

3. AGC - codes for 1 amino acid

TCT codes for a different a.a.

4.enzyme must open DNA double strand to make a working copy

a.messenger RNA (mRNA)

b.transcription

(1)process that makes mRNA from DNA

(2)requires RNA polymerase

(a)makes mRNA from DNA

(b)Uracil is used instead of Thymine

5.mRNA moves to the cytoplasm

6.ribosome (made of rRNA) attaches to the mRNA

7.ribosome reads mRNA

8.tRNA - transfer RNA

a.has the anticodon on one end

b.and the amino acid on the other end

c.binds to the mRNA and a peptide bond is formed between amino acids

9.Summary:

nucleus cytoplasm

DNA-------->mRNA-->ribosome + tRNA ---> protein

transcription translation

RNA polymerase

VI.Cell Growth and Reproduction

A.Cell Cycle

1.changes during the life of a cell

2.Interphase

a.G1, S, G2

(1)G1 = growth and normal metabolic activities of cell

(2)S = synthesis of DNA

(a)chromosomes replicate

(b)ready to divide

(3)G2 = enzymatic preparation for cell division

b.DNA replication

(1)need identical copies for each cell

(2)DNA uncoils from double helix

(3)opens up in a Replication Fork

(4)DNA polymerase

(a)enzyme that makes a polymer of DNA

(b)uses each strand as a template

(c)leading and lagging strand

(d)each daughter cell will have one template and one new complementary strand

(e)must pair

i)adenine - thymine

ii)cytosine - guanine