Lecture 6 - The Cell I Flashcards
describe the cell
simplest self-replicating entity that can exist as an independent unit of life
what do all cells have?
stable blueprint of information in molecular form (DNA)
- discrete boundary that separates the interior of the cell from its external environment
- ability to harness materials and energy from the environment
plasma membranes function
- physically separate the inside and outside of the cells
- create compartments within the cell (organelles/vacuoles/vesicles)
plasma membranes structure
- lipids
- proteins
- carbohydrates (glycolipids and glycoproteins)
what types of cells have plasma membranes
prokaryotic and eukaryotic
what are plasma membranes composed of
phospholipids
are membranes fluid?
yes
the phospholipids that form plasma membranes can do what type of movements
- turn on their axis
- move laterally in any direction over the surface of the membrane
- flipping across the membrane (inside to out) occurs very rarely
what happens to plasma membranes when the temperature lowers
- membranes go from a fluid state to a solid state
- temperature at which a membrane solidifies depends on types of lipids
in what state must plasma membranes be to work properly
- membranes must be fluid to work properly; they are usually about as fluid as oil
what is plasma membrane fluidity affected by?
- type of fatty acid chain
- presence of cholesterol
effect of type pf fatty acid chain on membrane fluidity
- membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
effect of the presence of cholesterol on membrane fluidity
- effect depends on temperature
- cholesterol reduces membrane fluidity at moderate temperatures by reducing phospholipid movement, but at low temperatures it hinders solidification by disrupting the regular packing of phospholipids
How could a cell change its membrane in response to very cold temperatures?
the type of fatty acid in phospholipids would be unsaturated
there would be lots of cholesterol
what is a membrane (made of)
a collage of different proteins, often grouped together, embedded in fluid matrix of lipid bilayer
what do membrane proteins do
determine most of the membrane’s specific functions
name types of membrane proteins
- integral membrane proteins
- peripheral membrane proteins
integral membrane proteins
- go from the outside of the membrane (go through it)
- composed of three regions: 2 hydrophilic and one hydrophobic region
- permanently associated with the cell membrane
peripheral membrane proteins
- temporarily associated with integral membrane proteins through weak noncovalent interactions (H-bonds) (on outside)
- easily separated from the membrane
- play a role in transmitting information received from external signals
membrane carbohydrates (include glycolipids and glycoproteins)
- involved in cell to cell recognition
- located outside of membrane
- glycolypids: carbs covalently bonded to lipids
- glycoproteins: carbs covalently bonded to proteins
fluid mosaic model
describes cell membranes:
- plasma membranes are fluid because of phospholipids and cholesterol
- plasma membranes are described as a mosaic because of the proteins, glycoproteins and glycolipids embedded within the membrane
plasma membranes function
- separate the inside from the outside of the cell
- maintains homeostasis (the active maintenance of the constant environment)
- exhibits selective permeability, allowing some substances to cross it more easily than others
the cell wall (location)
found outside of the plasma membranes of prokaryotic cells as well as those of plant and fungal cells
cell wall (function)
- provides structural support and protection
- resists expansion and allows pressure (turgor pressure) to build up in a cell when it absorbs water
turgor pressure
force exerted by water pressing against an object
provides structural support
cell wall structure
- rigid structure made or carbohydrates and proteins that surrounds the plasma membrane
what are the following types of cell walls made of
- plant
- fungi
- bacteria
- plant - polysaccharides (ex cellulose)
- fungi - polysaccharides (ex. chitin)
- bacteria - glycoprotein (peptitoglycan)
name cell adhesion types
- tight junction
- desmosome
- gap junction
tight junction
- prevent leakages of extracellular fluid across a layer of epithelial cells by forming continuous seals around the cells
- tight junctions between skin cells make us watertight
desmosome
- function live RIVETS, fastening cells together in strong sheets
- intermediate filaments anchor desmosomes together
- attach muscle cells to each other
gap junction
provide cytoplasmic channels from one cell to an adjacent cell
extracellular matrix overview
provides molecular framework that ultimately determines the structural architecture of plants and animals
in both plants and animals, contributes to structural support and provides informational cues that determine the activity of the cells.
ECM of animals
- found in most tissues (abundant in connective tissue)
- mainly composed of glycoproteins and tiher carbohydrate-containing “fibrous” molecules (elastin and collagen)
how are collagen and other fibers involved in ECM of animals
they’re embedded in a network woven out of proteoglycans secreted by cells (fibroblasts)
how are cells attached to ECM
by special ECM glycoproteins, such as fibronectin
fibronectin is bound to what
bound to cell-surface receptor proteins called integrins, that are built into the plasma membrane
within cytoplasms, integrins are bound to _______.
microfilaments
integrins transmit signals between what
the ECM and the cytoskeleton and thus integrate changes occurring outside and inside the cell
by communicating through integrins, what can the ECM do?
the ECM can regulate a cell’s function, structure, and behaviour
- the integrins recieve a signal and transmit it to the nucleus via microfilaments
- this may trigger signaling pathways inside the cell and nucleus that lead to changes in the set of proteins being synthesized
what is the path of a signal being sent from one cell to another
nucleous -> cytoskeleton (microfilaments) -> integrins -> fibronectin -> collagen
(opposite path is for receiving signal from outside cell)
why are most cells small?
due to reliance on diffusion of substances in and out of cells
cells work all the time, constantly performing chem reactions, thus need energy and to remove all waste produced
bc of requirements for homeostasis
metobolic demands are determined by volume but transport of materials is determined by surface area
cells require sufficient area to support cell’s metabolic needs, keeps cell small
where do materials pass in and out
cell surface
