2.2 - Why is CF mucus sticky? Flashcards
done
Why is CF mucus so sticky?
People with CF have less water in their mucus making it thicker than normal. The reduced water level is due to abnormal salt and water transport across the cell surface membranes caused by a faulty transport protein channel to the membrane
Where does protein synthesis occur?
Ribosomes
What are the two parts of an amino acid called?
Amine group and carboxylic acid group
What are proteins used for?
Structural Tendons, cartilage, hair, nails
Contractile Muscles
Transport Haemoglobin
Storage Milk
Hormonal Insulin, growth hormone
Enzyme Catalyses reactions in cells
Protection Immune response
Amino acid structure
H H O
| | ||
H - N - C - C - OH
|
R
amino carboxyl group
groupWhat atoms are in an amino acid?
carbon, oxygen, nitrogen, hydrogen and sometimes sulfur
What are dipeptides?
2 amino acid
What are peptides?
Chain of amino acids
What are polypetides?
many amino acids joined
Condensation reaction forming a dipeptide
- a carboxyl group condenses with an amino group in condensation reaction, releasing water
- amino acid sequence is called the primary structure
What is hydrolysis?
- splitting using water
- used to break peptide bonds
What is the primary structure?
- polypeptide chain
- sequence of amino acids held by peptide bonds
What is the secondary structure?
- held together by hydrogen bonds between O and H atoms
- alpha helix or beta-pleated sheet
What is the tertiary structure?
- 3D shape
- single polypeptide chain “backbone” with one or more protein secondary structures
- held together by bonds called; disulfide bridges, ionic bonds, van der waals attractions and hydrophobic exclusions
What is the quaternary structure?
- exists in proteins consisting of two or more identical or different polypeptide chains
What are peptide bonds?
Occurs between two amino acids between CO and NH atoms. Holds the primary structure in place
What are hydrogen bonds?
Occurs between O and H atoms in the secondary structures of proteins (alpha helix and beta sheet). Holds amino acids in these structures
What does hydrophilic / polar mean?
- water loving as they are attracted to water molecules
- molecules that have dipoles are hydrophilic
What does hydrophobic / non polar mean?
- They are water hating and so are not attracted to water molecules (tend to be insoluble in water)
- molecules that do not have dipoles are hydrophobic
What are disulphide bonds?
- Occurs between R groups of different amino acids that contain sulphur and hydrogen groups
- A single covalent bond (electrons shared)
- Shown as S-S
- Holds amino acids in tertiary structures
What are ionic bonds?
- Occurs between ionised (charged) R groups of amino acids
- A negative R group from one amino acid is attracted to a positive R group
from another amino acid
R+ —– R-
What are Van der Waals/ attractions?
- An attractive / repulsive force between molecules due to their electron clouds.
- These forces are weak but play an important role in biochemistry
Features of globular proteins?
- Small
- Soluble
- 3D shape / folded
- Tertiary structure
- Little repetition
- Hydrophobic groups point in – hydrophilic out – so often soluble
- eg Enzymes and hormones
Features of fibrous proteins?
- Long strands (large)
- Insoluble
- Hydrophobic on outside
- Mainly secondary structure
- Repeated amino acid sequence
- Structural role
- eg Keratin, Collagen
What is the phospholipid bilayer?
- Phospholipids form a bilayer around the cell
- Two layers of phospholipids with hydrophobic tails protected inside by the hydrophilic heads.
- The phospholipid is the basic structure of membranes.
What do membranes contain?
- phospholipid bilayer
- Proteins
- Cholesterol
- Glycoproteins - protein molecules with a polysaccharide attached
- Glycolipids - lipid molecules with a polysaccharide attached
Where are intrinsic proteins found?
span the cell membrane
Where are extrinsic proteins found?
sit on the outside of the cell membrane
What do phospholipids control?
how fluid the membrane is
What do saturated/ unsaturated do to the fluidity of the membrane?
saturated - less fluid
unsaturated - more fluid
What is the model for the structure of the membrane called?
Fluid Mosaic model
FLUID- because individual phospholipids and proteins can move around freely within the layer, as if it is a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.
What are phospholipids made up of?
Phosphate head and fatty acid tail
What are glycoproteins?
A protein which has a short branching carbohydrate chain. These act as receptors like glycolipids. Glycoproteins also act as antigens allowing cells to recognise each other.
What are glycolipids?
A lipid which has a short branching carbohydrate chain. These act as receptors, binding with substances like hormones. Cells have receptors specific to their function e.g. only liver and muscle cells have insulin receptors
How substances pass through cell membrane?
Diffusion Facilitated diffusion Osmosis Active transport Exocytosis endocytosis
What is diffusion?
- the net movement of molecules or ions from a region where they are at a high concentration to a lower concentration, particles are continually moving randomly in all directions.
- Diffusion will always occur when there is a difference in concentration between two areas, known as concentration gradient
- Diffusion will continue until equilibrium
What is facilitated diffusion?
Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also charged ions such as Na+ or Cl- cannot cross the bilayer.
These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.
Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.
What is osmosis?
Net movement of water molecules from a solution with a lower concentration of solute to a solution with a higher concentration of solute through a partially permeable membrane
What is active transport?
Active transport requires energy because the molecules move against a concentration gradient.
The energy is supplied by the molecule ATP which is produced by respiration.
The energy is used to make the transport protein change its 3D shape, transferring the molecules or ions across the membrane in the process.
What is exocytosis?
Exocytosis is the release of substances, usually proteins or polysaccharides, from the cell. Vesicles fuse with the cell membrane and the contents are released.
For example, insulin is released into the blood by exocytosis
What is endocytosis?
Substances are taken into a cell by creations of a vesicle from the cell surface membrane. Part of the cell membrane engulfs the solid or liquid material to be transported.
For example, white blood cells ingest bacteria and other foreign particles by endocytosis.
What substances enter cells?
oxygen and glucose
What substances enter and leave cells?
water and ions
What substances leave cells?
carbon dioxide and urea
What 4 factors affect the diffusion?
Steepness of the concentration gradient, temperature, surface area and type of molecule or ion diffusing
What is a solute?
solids that dissolve into liquid
What is a solvent?
a liquid that a solid can dissolve into
What is a solution?
when a solid has dissolved into a liquid
What does hypotonic, hypertonic and isotonic mean?
- hypertonic solution - concentrated solution
- hypotonic solution - dilute solution
- isotonic solution - solution with the same concentration as a cell’s cytoplasm
What happens to animal cells in each of the solutions (hypo, iso, hyper)?
Hypertonic - shriveled
Isotonic - normal
Hypotonic - lysed
What happens to plant cells in each of the solutions (hypo, iso, hyper)?
Hypertonic - plasmolyzed
Isotonic - flaccid
Hypotonic - turgid (normal)
What happens if there is excess water?
- Na+ moves out of cell by active transport, so concentration inside the cell falls
- Na+ ions now move out of mucus into cell by facilitated diffusion through ENaC
- There is now an electrical gradient, so Cl- moves in between the gaps of the cells
- Na+ and Cl- concentration is higher in the tissue fluid and so water moves out of the cell and out of the mucus to dilute the tissue fluid.
What happens if there is too little water?
Cl- are transported into the cells across basal membrane, this leads to an increase in Cl- inside the cell, and this causes the CFTR channel to open
The CFTR is a special gated protein channel
Cl- leaves apical membrane through the CFTR channel.
The open CFTR channel blocks the ENaC
There is a build up of Cl- which creates an electrical gradient between the mucus and the fluid. Na+ ions move out of the fluid and into the mucus. Water is drawn out of the cells and into mucus by osmosis.
What happens in CF?
CFTR protein is missing or non functioning
so Cl- cannot leave the cells.
ENaCs are not blocked and so Na+ enters the cell.
Raised levels of Na+ draws water and Cl- into the cell and out of the mucus.
Mucus is viscous and hard for the cilia to move.
Gas exchange is reduced and bacteria build up. Phagocytes are produced to destroy bacteria but this leads to more inflammation and damage.
