Cells and membranes

• what happens if an animal and plant cells are placed in a hypertonic solution?

  Animal= cell to shrivel

  Plant = cell to plasmolyse
• what happens if an animal and plant cells are placed in a hypotonic solution?

  animal = Cell to burst/haemolyse

  Plant = cell to become turgid
• what is a hypotonic solution?

  it has a higher water potential, i.e. a higher concentration of free water molecules in the cell cytoplasm
• What is a isotonic solution?

  it has the same water potential as the cell, and no net movement of water molecules
• What is a hypertonic solution?

  it has a lower water potential, i.e. I lower concentration of free water molecules than in the cell cytoplasm
• what unit is water potential measured in?

  kilopascals (kPa)
• What is water potential?

  The ' measure of the ability of water molecules to move freely in a solution
• What is osmosis?

  movement of water from an area of higher water, potential to an area of lower water potential, down a water potential gradient across the phospholipid, bilayer, or via protein channels (aquaporins)
• What factors affect the rate of facilitated diffusion?

  The concentration gradient

  Temperature

  The number of channel or carrier proteins
• what do carrier proteins do?

  allow specific large molecules to pass through. when the molecule binds to a specific site on the carrier, the protein changes, shape and transfers, the molecule to the other side of the membrane
• what do channel proteins do?


  actors pause in the membrane, some only allow specific ions, through, they can be gated, so they only open/close in specific circumstances
• What is facilitated diffusion?

  The movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient across a membrane via carrier and channel proteins
• What factors affect the rate of diffusion?

  -temperature= the higher the temperature, The higher the kinetic energy= increased rate

  -Concentration gradient= higher the gradient, the bigger, the difference in concentration from one side to another= increased rate

  -Thickness of exchange surface = thicker exchange surface, larger distance for molecules to move = decreased rate
• what molecules diffuse through the bilayer?

  lipid soluble (steroid hormones - testosterone)

  Small and nonpolar (oxygen)

  Very small and polar (water - slowly)
• what is simple diffusion?

  The movement of substances from an area of high concentration to an area of low concentration down a concentration gradient across a partially permeable membrane directly through the phospholipid bilayer
• what is the procedure for required practical 4: investigating cell membrane permeability? (part two)


  9) place each test tube in turn into the colorimeter and read the absorption recording your results in a suitable table

  10) plus a graph of absorption against temperature
• what is the procedure for required practical 4: investigating cell membrane permeability?

  1) Prepare six water baths present to a range of temperatures: 30-80 degrees

  2) use a syringe to add 10 cm³ of distilled water (buffered to pH seven) 26 test tubes. Label each test tube with a temperature from the present range.

  3) place each tube into the corresponding temperature water bath for five minutes

  4) check the temperature is correct using your thermometer

  5) using a scalpel, ruler and white tile, cut six beetroot chip to the same length. Wash the cylinders thoroughly with distilled water and pat dry with a paper towel.

  6) add one featuring Chip to each of the six tubes only for 10 minutes. Prepare table for your results.

  7) now shake the test tubes once, and then, using a mounted needle in carefully, stab the cylinders and remove from each test tube. This can be discarded.

  8) set the colorimeter to green filter and absorption. Zero colorimeter, using a blank test-tube filled with distilled water.
• what is the relationship between temperature and membranes?

  Increase in temperature, increases kinetic energy of phospholipids and protein molecules in the membrane, molecules being transported, also have more kinetic energy and come diffuse across the membrane more quickly.

  However, when the increase in temperature is too much, protein denature, making the membrane more permeable, also the phospholipid membrane becomes more fluid and permeable, and this causes gaps to open temporarily in the bilayer and resorts in ions/molecules diffusing more quickly

  Further increase in temperature causes the membrane to be destroyed ions/molecules diffuse in the first few moments of experiment and reach equilibrium quickly
• what are (phospholipid) cell membranes?

  -partially permeable barriers

  - Made up a phospholipid molecules arranged in a bilayer and proteins

  - Under an electron microscope you can see the bilayer is too dark bands. The distance across the membrane is about 7 nm.
• what do akaryotes (viruses) do/contain?

  nucleic acid surrounded by protein

  DNA/RNA, attachment proteins (antigens), capsid (protein coat)

  They inject the DNA/RNA into the host cell, the host cell, then produces the viral components, which are assembled into new viruses

  They attach to the host cell surface (attachment, proteins, bind to complimentary receptor proteins), then inject their genetic material into the host cell
• What does MRS GREN stand for?

  Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition
• how do antibiotics work?

  One way is preventing bacteria from making normal cell walls

  Penicillin works by inhibiting certain enzymes required for the synthesis and assembly of the peptide cross linkages (chemical bonds) in bacterial cell walls this week and the walls, making them on able to withstand pressure as water enters by osmosis. The cell then bursts and the bacterium dies.
• What are the steps for binary fission?

  1) circular DNA and plasmid replicate main DNA loop is only replicated once plasmids can replicate lots

  2) Bissell gets bigger, DNA loops move to opposite poles (ends) of this cell

  3) cytoplasm begins to divide (and new cell walls begin to form)

  4) the cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have variable numbers of copies of the plasmids.
• what do prokaryotic cells contain?

  Peptidoglycon/murein cell wall

  Capsule

  Plasmid

  Nucleoid

  mesosome

  Flagellum

  Cytoplasm

  70S ribosomes

  Cell surface membrane
• What does the cytoskeleton do/contain?

  -network of protein fibres which provide support and give shape to the cell

  -Holds organelles in place or allows them to move through the cytoplasm

  -Responsible for the movement of the chromosomes during cell division

  -Involved in changing the shape of the cell surface membrane during Endo/exocytosis
• why do protein receptors found on target cells have a specific shape?

  protein receptors found on target cells have a specific shape complimentary only to a specific hormone (or neurotransmitter)

  They will bind with the hormone to allow the cell to respond a particular way
• what is cell signalling?

  -processes that lead to communication and coordination between cells, so that they can work together to trigger a response

  -Also allows cells to be recognised as self and so prevent cells from being destroyed by the immune system

  -A receptor in the cells, plasma membrane, detects chemical signals, and brings about responses within the cell
• what are the roles of cell membranes at the surface of cells?

  to separate cell contents from the outside environment

  Cell recognition and signalling

  Regulating transport of materials into or out of the cells

  Create/maintain concentration gradients
• What are the roles of cell membranes within cells?

  they separate cells from cytoplasm (compartmentalisation)

  holds components of metabolic pathways in place (enzymes in mitochondria)

  Controls what enters and leaves the organelle

  Sites of attachment
• what do you glycoproteins do in a cell membrane?

  proteins with carbohydrate attached

  receptors for signalling molecules

  Cell signalling and recognition (cell surface antigens)

  Finding cells together to basement membrane (protein structure) making tissues, cell adhesion
• What do extrinsic proteins do in the cell membrane?

  inter cell signalling

  cell recognition

  Enzymes

  Receptors for signalling between cells, hormone receptors etc

  Cell adhesion
• What do intrinsic proteins do in the cell membrane?

  Channel or carrier proteins that allowed transport of hydrophilic, Polar molecules (like glucose) and ions through the phospholipid bilayer.
• what do glycolipids do in the cell membrane?

  phospholipids with carbohydrate attached

  Inter cell signalling and recognition

  Cell adhesion, helps to stick cells together and two basement membranes to form tissues
• what does cholesterol do in the cell membrane?

  found in eukaryotic cells for stability and fluidity of the cell membrane

  Steroid molecule that fits between fatty acid tails, completing the membrane barrier to water and ions

  Binds to the hydrophobic tails of the phospholipids, they prevent the membrane being to fluid at high temperatures, but also stops the membrane solidifying at low temperatures
• what do you cell membranes contain?

  phospholipids, hydrophobic tail and hydrophilic head

  Cholesterol

  Glycolipids

  Proteins, intrinsic and extrinsic

  Glycoproteins
• describe the fluid mosaic model of cell membranes.

  -component molecules aren't bonded together, so there is some movement but it is relatively stable because of the nature of the phospholipid

  -Singer and Nicholson, 1972 fluid mosaic model

  Fluid = phospholipids and proteins are free to move, laterally (sideways)

  Mosaic = proteins have a scattered arrangement within the phospholipid bilayer
• what do phospholipids do in the cell membrane?

  -make up most of the plasma membrane, arranged in a bilayer (hydrophobic tail faces inwards, hydrophilic head faces outward)

  -they act as a barrier to water soluble, polar molecules and ions

  - allows lipid soluble, small, non-polar substances to diffuse through (oxygen, carbon dioxide, steroid hormones)

  - makes the membrane flexible and self - sealing making end and exocytosis possible.
• what does the cell wall do and contain?

  in plants = made of cellulose (polymers of ß glucose)

  fungi = made of a complex polysaccharide (chitin)

  bacteria = peptidoglycan or murein

  - provides a strong wall for support and strength in the plant and to prevent cells bursting
• what does the permanent vacuole do and contain?

  - cell sap, tonoplast

  - fluid filled sac surrounded by a single membrane called a tonoplast

  - contains variable amounts of water, mineral salts, sugars, amino acids, waste and sometimes pigments

  - it maintains cell turgidity (stiffness), by pushing cytoplasm against the cell wall.

  - together lots of turgid cells help to support the plant

  - its also involved in the isolation of unwanted chemicals
• what do ribosomes do and contain?

  -no membrane (they are found on the surface of the RER and in cytoplasm.

  -they have two subunits (one large and one small) each contains ribosomal RNA and proteins.

  - the site pf protein synthesis

  -mRNA (from the nucleus) is decoded by ribosomes to assemble a sequence of amino acids to synthesise a polypeptide (protein)