Homeostasis and cell membranes

Homeostasis

active maintenance of a stable internal conditions

What are the two types of factors homeostasis regulates

External and endogenous (self-imposed)

Which organisms have homeostasis

Everything except viruses

Two types of organisms when we look at homeostasis

Conformers (do not maintain it but need to stay within range to survive) and regulators (actively go through homeostasis loops)

negative feedback loop

stimulus, sensor, action or response that OPPOSES what is sensed by the stimulus

positive feedback loop

stimulus, sensor, action or response that agrees with what is sensed by the stimulus

Nucleus

houses the cells DNA

Cell membrane

semipermeable phospholipid bilayer surrounding every cell

Prokaryotic cells

cells with no nucleus

Eukaryotic cells

cells with a nucleus

Transcription

DNA is copied into messenger RNA

Translation

Proteins are synthesized from messenger RNA

Central dogma (of molecular biology)

theory describing the pathway from DNA to RNA to proteins

Gene

DNA sequence that accounts for a certain portion

DNA replication

allows it to be passed on to the cells offspring

ATP

created by chemical reactions breaking down molecules to release an accessible form of chemical chemical energy known as ATP

The three principles of cell theory

• all organisms are made up of cells

• the cell is a fundamental unit of life

• all cells come from pre-existing cells

Label this diagram of a phospholipid

Points you should be able to point out: hydrophilic head made up of choline, phosphate and a glycerol backbone, and the hydrophobic tail made up one saturated and one unsaturated fatty acid

What is the shape of the two kinds of fatty acids

a saturated fatty acid is straight because it only has single bonds whereas an unsaturated fatty acid is bent because of the double bond in it

Amphipathic

Both hydrophilic (water loving) and hydrophobic (water hating)

Affect of cholesterol on membrane fluidity

Opposite effect of the usual fluidity - at high temperatures cholesterol decreases membrane fluidity and vice verss

Lipid rafts

defined patches of things like cholesterol

Protens that associate with cell membranes

Transporter, receptors, enzyme, anchor

Transporter

move ions or molecules across the membrane

Receptores

allow cell to recieve signals from the environment

Enzyme

catalyzes chemical reactions

Anchor

attaches to other proteins and helps maintain cell structure and shape

Integral membrane proteins

permanently associated with cell membranes

Peripheral membrane proteins

temporarily associated with the cell membrane

What is a transmembrane protien

an integral membrane protein that spans the entire lipid bilayer

What is a transmembrane proteins composed of

Two hydrophilic regions on opposite sides of the membrane and one hydrophobic region on the interior of the membrane

What can cross the cell membrane without help

gases and non polar molecules

What can NOT cross the cell membrane without help

macromolecules, proteins, ions and charged molecules

Passive transport

occurs when molecules move across a cell membrane through diffusion

Diffusion

movement of substances from area of higher to lower concentration

Simple diffusion

straight through the membrane

Facilitated diffusion

moves down a concentration gradient through a protein transporter

Two types of membrane transporters

Channel proteins and carrier proteins

Channel protein

provides an opening between the outside an inside that facilitates passive transport

Carrier protein

Binds to the molecule and pushes it through instead of js a gaping hole meaning it can preform passive transport (slower than channel proteins) and active transport (low to high concentration)

Aquaporins

channel proteins that allow water to move more readily across a cell membrane with facilitated diffusion

Does water only rely on aquaporins

Even though it is poor it can move through the cell membrane because it is so small but only to a limited extent

Osmosis

net movement of water across a selectively permeable membrane from an area of lower to higher solute concentration

osmotic pressure

describes tendency of a solution draw water in by osmosis

active transport

moving molecules through cell membranes against the concentration gradient (from high to low)

Primary active transport

uses metabolic energy directly (typically ATP) to move waste through the cell membrane

secondary active transport

move molecules against heir concentration gradient using energy stored in an electrochemical gradient instead of directly using ATP

Contractile vacuoles

organelle that take up excess water from inside the cell and then expel them into the external environment by contracting

Cell wall

a well surrounding the cell membrane made up of many components depending on the organism