2.5 - Biological membranes Flashcards Preview

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Flashcards in 2.5 - Biological membranes Deck (8)
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1
Q

Components and fuctions of cell surface membrane

A
  • phospholipids form bilayer (phospholipid hydrophobic tails pointing inwards and hydrophilic
    heads pointing out)
    Role: provide barrier to large / polar / molecules and ions
  • proteins form carrier or channel proteins across membrane
    Role: for active transport / facilitated diffusion
  • cholesterol molecules fit between phospholipids
    Role: stabilise membrane structure and regulates fluidity
  • glycoproteins
    Role: act as receptors for cell communication
2
Q

Roles of cell surface membranes inside cells

A
  • form edge of organelles within a cell
  • isolation of contents of organelles from cytoplasm
  • site for attachment of enzymes and ribosomes (on RER)
  • provide selective permeability, controls what enters and leaves organelles
  • separating areas of differing concentrations to provide gradients
3
Q

Cell signalling – how receptors work

A
  • release of signal molecule e.g. hormone by exocytosis into the blood
  • proteins / glycoproteins / glycolipids act as receptors (for e.g. hormones/drugs)
  • receptor is specific as the shape of receptor and hormone are complementary in shape
  • hormone binds to receptors
  • binding causes change inside cell and brings about a response
4
Q

Role of glycoproteins

A
  • Cell signalling - communication between cells to help them work together
  • Act as antigens for…
  • cell recognition - recognition as self/non-self
  • receptors found on target cells
  • for hormones/cytokines to trigger reactions/responses in cells
  • cell adhesion - hold cells together in tissues
  • form bonds with water molecules to stabilise membrane
  • receptors on transport proteins
5
Q

Substances crossing membranes

A

small, non-polar substances
- diffuse through phospholipid bilayer

large substances

  • using carrier proteins
  • specific to certain molecules
  • protein changes shape to allow molecule through to other side
  • facilitated diffusion/active transport (use ATP against the gradient, faster, one way)
  • endocytosis / exocytosis
  • bulk transport

polar substances

  • through channel proteins
  • facilitated diffusion
6
Q

Compare active transport and facilitated diffusion

A

Proteins involved
AT - carrier proteins (protein pumps)
FD - Carrier proteins and channel proteins

What is carried
AT - anything from a low to high conc.
FD - larger molecules e.g. glucose Ions/polar molecules e.g. K+ and Ca2+

7
Q

Compare the roles of carrier proteins and channel proteins and how they work

A

Carrier proteins:

  • specific to molecule it carrier
  • molecules attach on one side of the membrane
  • the protein changes shape
  • releases molecules on the other side of the membrane
  • Carries large molecules across the membrane in facilitated diffusion (doesn’t require energy)
  • Carries all molecules across the membrane in active transport which does require energy.

Channel proteins:

  • specific to molecule it carrier
  • forms a pore through the centre of the protein
  • creates hydrophilic conditions in the pore
  • Allows charged and polar substances across the membrane in facilitated diffusion
8
Q

Movement of molecules

A
  • Diffusion -the net movement of molecules from a region of high concentration of that
    molecule to a region of lower concentration of that molecule down a concentration gradient.
    This is a passive process.
  • Facilitated Diffusion -the net movement of molecules from a region of high concentration of
    that molecule to a region of lower concentration of that molecule down a concentration gradient through carrier proteins (large molecules) or channel proteins (ions). This is a passive process.
  • Active transport - is the movement of molecules or ions across a membrane from a region of low concentration to a region of higher concentration of that molecule, against the concentration gradient. This process uses ATP to drive the protein ‘pumps’ within the membrane.
  • Osmosis - the net movement of water molecules from a region of high water potential to an area of lower water potential, down the water potential gradient across a partially permeable membrane. This is a passive process.