Paper 1 - Digestion Flashcards
Digestion of carbohydrates
- Salivary amylase hydrolyses the glycosidic bonds in starch to produce maltose
- Acid in stomach denatures the salivary amylase
- So pancreatic amylase is released into the small intestine to continue the hydrolysis
- Maltase, from the membranes of the epithelial cells, hydrolyses maltose into glucose
Absorption of carbohydrates
Monosaccharides are transported across the membrane of the epithelial cells in the ileum via transporter proteins.
Glucose is absorbed with sodium ions via co-transport.
Galactose also uses a co transporter protein
Fructose is absorbed using facilitated diffusion
Absorption of glucose through co-transport
- Na+ actively transports out of the epithelial cell into the blood using the Na/K pump
- This lowers the concentration of Na+ inside the epithelial cells.
- Na+ moves down its conc gradient from the ileum into the epithelial cell via the sodium-glucose transporter by facilitated diffusion. Glucose was also taken, against its own concentration gradient.
- Glucose moves out of the cell via facilitated diffusion into the blood
Digestion of proteins
Endopeptidases → hydrolyse peptide bonds in the middle - found in the stomach and SI
Exopeptidases → hydrolyse peptide bonds of amino acids at end - found in SI
Dipeptidases → hydrolyse peptide bonds between amino acids in dipeptides
Immune response - Phagocytosis
- Phagocyte receptors bind to foreign antigens on the surface of pathogen.
- Phagocyte engulfs pathogen by endocytosis
- Pathogen is contained in phagocytosis vesicle
- Lysosome fuses with phagocytes vesicle, lysozymes digest the pathogen.
- Phagocyte presents antigens on cell-surface membrane = antigen presenting cell
Digestion of lipids
l. Fat globules are emulsified by bile
2. Lipases hydrolyse lipids into monoglycerides and fatty acids
3. These aggregate with bile salts to form micelles
Absorption of lipids
Adaptations of the small intestine
Large surface area
Lots of capillaries - continuous supply of blood - maintains the concentration gradient
Thin walls = short diffusion pathway
Lots of mitochondria to release ATP for active transport
Immune response - Cell Mediated Response
- Helper T cell with complimentary receptor to antigen presented on phagocyte binds
- T cell becomes activated and rapidly divides by mitosis into 3 types of T cell:
- Cytotoxic (killer) T cells
- Helper T cells release cytokines that stimulates more phagocytes, B cells and killer T cells
- Memory T cells which recognise the antigen enabling a rapid response
Immune response - Humoral
- B-cell with complimentary antibody to antigen binds to antibodies on membrane.
- This is activated by helper T cell
- B cell divides rapidly by clonal selection and produces 2 types of B cell:
- Memory B cells → divides rapidly and produce correct AB in the secondary immune response if pathogen re-enters the body
- Plasma B cells → rapidly secrete monoclonal ABs complimentary to the antigens = agglutination of pathogens and stimulates phagocytosis.
How vaccines lead to antibody production (immunity)
- Vaccine contains antigen from the pathogen.
- Phagocyte engulfs and digests pathogen and presents antigen on surface
- Helper T cell with complimentary receptor binds to antigen and is activated.
- Helper T ce
Direct ELISA test
- Antigens from patient sample are stuck to the bottom of the well
- Monoclonal antibody with enzyme attached is added - mAB is complementary to the antigen so will bind if antigen is present
- Wash to remove unbound mAB
- Colourless substrate solution added - if mAB is bound and present, enzyme attached will convert substrate to a coloured solution
Indirect ELISA test
- Antigens are immobilised at bottom of well
- Patient sample of antibodies added - if antibody present, it will be complimentary to the antigen in the well and bind
- A secondary mAB complimentary to patient antibody is added with an enzyme attached - if antibody was present, the secondary mAB will bind
- Wash to remove unbound antibodies
- Colourless substrate solution is added - if antibodies is present, enzyme attached will convert substrate to a coloured solution
HIV replication
- Attachment proteins on HIV attach complimentary CD4 receptors on helper T cell
- RNA enters cell
- Reverse transcriptase converts RNA to DNA which is transcribed and translated by helper T cell ribosomes
- Viral proteins produced
- Virus assembled and released, destroying the cell
