THE CELLULAR LEVEL OF ORGANIZATION Cell – basic structural and functional unit of life; enclosed by a

membraneCell Theory * All living things are composed of one or more cells;* The chemical reactions of living cells take place within cells;* All cells originate from pre-existing cells; and* Cells contain hereditary information,which is passed from one generation to another.Types of cell according to their nucleus:1. Prokaryotes – organisms lack membrane-bound organellespro – before, karyo- nucleus2. Eukaryotes - cells display a much greater degree of structural organization and complexityeu – true, karyo- nucleus

GENERAL COMPONENTS OF CELLS1. CELL MEMBRANE -

3 divisions of a cell structure: 1. plasma membrane 2. cytoplasm 3. nucleusA. PLASMA MEMBRANE

- boundary between the outside and inside environments

•selectively permeable/ semi-permeable•regulates flow of materials into and out of the cell•also provides communication among and between cells and their external environment•made up of lipids and proteins•fluidity – movement of bilayer; self-seals during injury; changes position in the bilayer (but not flip-flopping); cholesterol component provides strength at normal body temperature; becomes fluid at low temperatures

PROKARYOTIC CELL- A type of cell that lacks a membrane bounded nucleus and the DNA is not physically separated from the rest of the cytoplasm. The DNA is usually coiled, attached to the plasma membrane and concentrated in a region of the cell called the NUCLEOID.- Are usually very small (less than 5 u in length) with relatively simple internal structure and are mostly surrounded by a relatively stiff cell wall.Ex. bacteria (Kingdom Monera)

 EUKARYOTIC CELL- A Cell containing distinct membrane bounded nucleus as well as variety of membranous organelles that lend structural and functional organization to the cell interior

Figure 1. Cell structure

LIPIDSforms the basic structural framework2 layers of phospholipid (75%), cholesterol (20%) and glycolipids (5%)phospholipids – amphipathic molecules (hydrophilic heads – arranged outward and hydrophobic tails – arranged inwards)glycolipids – made up of carbohydrate and lipids; positioned outside of the membranecholesterol – interspersed on both sides PROTEINS types: integral proteins – extended into or through the lipid bilayer; forms transmembrane proteins (protrudes on both sides) peripheral proteins – associate with polar heads of lipids or with integral proteinsglycoproteins – carbohydrate + proteins; forms a sugary coating outside; also forms identity markers

Functions:

ion channel – pore but may also be selective

transporter – moves polar substances from one side to the other

receptor – recognition sites

cell identity markers – glycoproteins and glycolipids

linkers – anchor proteins in the plasma membrane of neighboring cells and to protein filaments inside and outside the cell

Figure 2. Parts of the Cell Membrane

HOW SUBSTANCES MOVEselective permeability

1. lipid bilayer is permeable to nonpolar substances and uncharged molecules like oxygen gas, carbon dioxide and steroids but are impermeable to charged ions or polar molecules

2. it is slightly permeable to water and urea (small gaps created through movement)

3. transmembrane proteins allows passage of ions

-protein molecules move in and out through endocytosis and exocytosis

-concentration gradient (high to low concentration) also permits entry and exit of ions (oxygen gas and sodium – outside; carbon dioxide and potassium – inside

- electrochemical gradient/ electrical potential results due to high concentrations of + and – ions; movement is down concentration gradient

- transport – substances needed for a chemical reaction inside; imports materials not produced by the cell; exports products (waste); 2 mechanisms: active and passive

a. active transport – against concentration gradient – low to high concentration; requires ATP expenditure; processes: exocytosis and endocytosis (pinocytosis & phagocytosis)b. passive transport – towards concentration gradient – high to low concentration; no ATP is used; processes: simple diffusion, facilitated diffusion and osmosis

SIMPLE DIFFUSION

- movement of particles from high to low concentration- factors influencing diffusion 1. steepness of concentration gradient – the higher the concentration the faster the diffusion process

2. temperature – at high temperature diffusion also hastens

3. mass of diffusing substances – the heavier the molecules diffusion tends to be slower

4. surface area – the more surfaces to attach to, the faster the diffusion process; emphysema – low SA thus person has difficulty in breathing

5. distance – the greater the distance to the surface the longer or slower the diffusion process; in pneumonia, the fluid collecting in the lungs creates a higher distance for diffusion of oxygen gas 

diffusion through the lipid bilayer - oxygen gas, carbon dioxide, nitrogen gas, fatty acids, steroids, and vitamins ADEK, small alcohols and ammonia, water and urea - does not contribute to tonicity 

membrane channels - ion channels; small inorganic ions; ion – specific channels; Cl and K; gated (changes shape)

FACILITATED DIFFUSION

- too polar or highly charged solutes; too big molecules- aided by carrier protein- transporter + solute = inside the cell (if transporter undergoes change in shape)- saturation – point at which all transporters are fully occupied; transport maximum is reached- glucose, fructose, galactose, some vitamins- example: glucose --> binds to glucose transporter (GluT) --> GluT changes shape --> inside --> GluT releases glucose --> glucose attaches to hexokinase (so that it cannot attach to GluT, thus preventing exit of glucose)- presence of insulin increases transport maximum of membrane proteins

 

OSMOSIS

- net movement of solvent in a semipermeable membrane- water moves from high concentration to low concentration- movement is through the phospholipid bilayer and aquaporins (protein channels for water)- osmotic pressure – pressure needed to stop the movement of water into a solution when solutes cannot pass through the membrane

tonicity – a measure of the solution’s ability to change the volume of cells by altering water content isotonic – equal concentration; 0.9% NaCl sol’n. – physiological saline hypotonic – lower concentration of solutes outside than inside the cell; results to swelling of the cell; used in rehydration (IV or oral); example: sportsdrinks – water from blood --> interstitial fluid --> inside cells hemolysis – rupture of RBC in a hypotonic solution hypertonic – high concentration of solutes outside than inside the cell; results in cell shrinkage; used to patients with cerebral edema (mannitol – relieves the overload due to osmosis from interstitial fluid --> blood --> kidney --> urine)  crenation – shrinkage of RBC’s

ACTIVE TRANSPORT

ions: Na, K, H, Ca, I, Cl; amino acids and monosaccharides primary active transport – protein transporter pumps substance inside; Na-K pumpsecondary active transport- symporters (move 2 molecules at the same time; example: Na-Glu, Na – amino acid)- antiporters – move out molecules (Na+/Ca2+; Na+/H+) 

endocytosis- forms a vesicle (sac made through pinching out of the membrane)- movement into the cell3 types1. receptor - mediated endocytosis---- binding to receptor --> invagination --> vesicle --> uncoating inside the cell --> fuse with endosome --> degradation in lysosomes 2. phagocytosis – engulfment of solid particles; cell-eating process; phagosome (vesicle); forms false feet (pseudopodia) for engulfment; macrophages and neutrophils (WBC) 3. pinocytosis – cell-drinking process; tiny droplets of ECF taken up; pinocytic vesicle 

exocytosis- movement out of the cell; secretion; digestive enzymes, hormones, mucus, neurotransmitters- secretory vesicles from inside the cell fuses with the plasma membrane going towards the ECF

B. CYTOPLASM

1.cytosol – sol-gel; 75 – 90% water; ions, glucose, amino acids, fatty acids, proteins, lipids, ATP and even waste products; site for chemical reactions

2. organelles – maintenance, growth and reproduction of the cell

organelles:2.cytoskeleton – provides framework; organizes contents and provides shape to cells; aids in movement of organelles

Figure 1. Cell structure

types: a. microfilaments – thinnest; made of actin; helps generate movement and provides mechanical supportb. intermediate filaments – in between microfilaments and microtubules; help stabilize position of organellesc. microtubules – thickest; made up of tubulin; helps determine cell shape and function; movement of chromosomes during cell divisiond. centrosome – forms centrioles; made up of tubuline. cilia – motile, short, hair-like projection; found in the tracheal wall and fallopian tubef. flagella – motile, longer than ciliary projection; sperm cells

CYTOSKELETON

Centriole/ centrosome

cilia

 2. golgi apparatus/ body/ complex- checks for quality of products manufactured by the cell- cis-trans face (entry-exit points); forms secretory vesicles for transport- double membrane organelle; made up of cisternae 

 

3. mitochondria (plural)/mitochondrion (singular)- powerhouse of the cell- where energy production occurs- sausage-shaped; made up of coils of cristae; double membrane

4. endoplasmic reticulum (ER)- synthesizing units; double membrane; made up of cisternae2 types: 1. smooth ER – for lipid synthesis, detoxification of drugs and alcohols, metabolism of fats2. rough ER – with attached ribosomes; where protein synthesis occurs  5. ribosomes – 2 types: attached (to ER) and free; where proteins are synthesized

RER

Ribosome

6. lysosomes – suicidal bags (due to acidity of its contents leakage can cause damage to the entire cell; example: neutrophils (WBC); contains hydrolytic enzymes which digests materials; webbing of fetus’ hands forms fingers due to suicide of lysossomes (autophagy) 

7. peroxisomes – transforms toxic H2O2 to water (nontoxic) upon lipid metabolism C. NUCLEUS - the brain of the cell; it directs the cell’s activities- enclosed by a nuclear envelope (double membrane)- materials from nucleus pass through the nuclear pore- nucleolus – contains chromatin material (DNA and RNA) needed for reproduction and for protein synthesis; during cell division chromatin material forms chromosomes for mitosis and meiosis.

Nucleus with nucleolus

Figure 1. Cell structure

VacuoleVacuoles are large empty appearing areas found

in the cytoplasm. They are usually found in plant cells where they store waste. As a plant cell ages they get larger. In mature cells they occupy most of the cytoplasm.

Cell WallCell WallProtects and supports plantCellsPrevents water lossCelluloseLocation: outer layer of plant cells

ChloroplastTraps suns energy and Makes foodLocation: in plant cells

PlastidsStores extra food in Plant cellsLocation: in plant cell