3 components of cell theory
- cells are the structural and functional unit of life
- all living things are composed of cells
- new cells are produced from existing cells
3 basic parts of a human cell
- plasma membrane (flexiable outer boundary)
- cytoplasm ( intracellular fluid containing organelles)
- nucleus is control center
plasma membrane (4)
- lipid bilayer and proteins in constantly changing fluid mosaic
- plays dynamic role in cellular activity
- separates intracellular fluid from extracellular fluid
- interstitial fluid that surrounds cell
membrane lipids
- 75% phospholipids
- phosphate heads: polar and hydrophilic
- fatty acid tails: non polar and hydrophobic
- lipids with polar sugar groups on outer membrane surface
- 20% cholesterol
what are the 2 membrane proteins
- integral
2. periphreal
integral proteins
transmembrane proteins that span the entire width of the membrane and are involved with transport as channels or carriers
periphreal proteins
not embedded in the plasma membrane, but attach to integral proteins or to phospholipids, and may function as enzymes or in mechanical functions of the cell
what are the 6 functions of membrane proteins
- transport
- receptors for signal transduction
- attachment to cytoskeleton and extracellular matrix
- enzymatic activity
- intercellular joining
- cell-cell recognition
transport
- a protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective or a particular solute (PASSIVE)
- some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane (ACTIVE)
receptors for signal transduction
- a membrane protein exposed to the outside of the cell may have binding site that fits the shape of a specific chemical messenger, such as a hormone
- when bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell
attatchement to cytoskeletons and extracellular matrix
- elements of the cytoskeleton (cells internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps MAINTAIN CELL SHAPES and fix the location of certain membrane proteins
- others play a role in cell movement or bind adjacent cells together
enzymatic activity
- a membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution
- a team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway
WHEN ATTATCHED TO CELL MEMBRANE
intercellular joining
- membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions
- some membrane proteins (cell adhesion molecules or CAMS) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions
the glycocalyx
“glyco” means sugar
“calyx” means cavity/ depression
-sugar covering at cell surface
- lipids and proteins with attached carbohydrates
-every cell has different pattern of sugars
-specific biological markers for cell recognition
- allows immune system to recognize “self” and “non self”
-cancerous cells change it continuously
SOME GLYOPROTEINS SERVE AS IDENTIFICATION TAGS THAT ARE RECOGNIZED BY OTHER CELLS
cell junctions
- some cells “free”
- blood cells, sperm cells
- some bound into communities
3 ways cells are bound:
- tight junctions
- desmosomes
- gap junctions
tight junctions
nothing can really pass through
desosomes
filaments attatch to each other to keep them from separating (SKIN)
plasma membrane (4)
- cells surrounded by interstitial fluid
- contains thousands of substances; amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products
- plasma membrane allows cell to obtain from IF exactly what it needs, exactly when it is needed
- keeps out what it does not need
plasma membrane transport
- selectively permeable
- non polar things can go through cell membrane (lipids)
- passive and active processes
passive membrane transport process
- no cellular energy required
- substances move down concentration gradient
active membrane transport process
- energy required
- occurs only in living cell membranes
2 types of passive processes
DIFFUSION:
-simple diffusion (perfume)
-carrier and channel mediated facilitated diffusion
-osmosis ( movement water from high to low concentration)
FILTRATION:
-usually across capillary walls (blood)
- driven by hydrostatic pressure, movement of molecules from high hydrostatic pressure to low hydrostatic pressure
membrane permeable to both solutes and water
solutes and molecules move down their concentration gradients in opposite directions. fluid volume remains the same in both compartments
NET MOVEMENT OF WATER TO THE RIGHT
MOVEMENT IS BOTH UNLESS NON PERMEABLE
END RESULT IS EQUILLIBRIUM
membrane permeable to water impermeable to solutes
solute molecules are prevented from moving but water moves by osmosis. volume increases in the compartment with the higher osmolarity
MOVEMENT OF WATER TO BOTH
NET MOVEMENT TO THE RIGHT
SOLUTE DOESNT MOVE
