Flashcards in Biochemistry Deck (556)
What is the function of cellulose?
Primary structural component of cell wall of green plants
Lignin and cellulose (lignocellulose) most common biopolymer on earth
Only tunicates evolved the ability to create and use cellulose
Indigestible by humans so acts as hydrophilic bulking agent for faeces
Describe the structure of cellulose
Layered linear chains of B-1,4 linked D-glucose units packed into crystals (myofibrils)
Layers linked by H bonds
What is lactose?
Disaccharide of B-D-galactose and B-D-glucose linked through B-1,4
What are glycosaminoglycans? (GAGs)
Large, pure carbohydrates that are -ve charged, hydrophilic
Polysaccharides present on animal cell surface and in ECM
Describe the structure of GAGs
Disaccharide repeating unit containing glucosamine or galactosamine and uronic acid
At least one of the sugars has a -ve charged carboxylate or sulphate group - with exception of hyaluronic acid (no sulphate group)
What is a glycoprotein?
Macromolecule composed of protein and a carbohydrate which is added in posttranslational modification either at asparagine (N-glycosylation) or hydroxylysine/hydroxyproline/serine/threonine (O-glycosylation)
What is the function of glycoproteins?
Assist protein folding or improve stability
Immune cell recognition: antibodies (immunoglobulins) interact directly with antigens, moles of major histocompatibility complex (MHC) surface of cells interact with T-cells (adaptive immune response)
Explain N and O glycosylation
Glycosylation is the attachment of carbohydrate to AA side chain
N: attach to N of amide side chain (asparagine)
O: attach to O of OH side chain (hydroxylysine/hydroxyproline/serine/threonine)
What are proteoglycans?
Heavily glycosylated glycoproteins - core protein with several GAG chains
What are the functions of GAGs?
Structural: ECM and BM
Space-filling in cartilage
Modifiers/activators of effector proteins (growth factors, proteases)
What are the functions of proteoglycans?
Form large complexes in ECM with proteoglycans and fibrous matrix proteins (collagen)
Binding of cations and water
Regulation of movement of molecules through matrix
What is chondroitin sulphate?
Sulphate GAG composed of N-acetyl-galactosamine and glucuronic acid
Usually forms part of a proteoglycan
What is the function of chondroitin sulphate?
Major structural component in cartilage conferring resistance to compression
Dietary supplement for treatment of osteoarthritis
What is heparin?
Highly sulphated GAG used as injectable anticoagulant and used for inside of test tubes, renal dialysis machines
Describe the structure of peptidoglycan
Crystal lattice of linear chains of NAG and NAM
Each NAM has peptide chain usually containing AAs that do not occur in humans thought to protect against attacks by most peptidases
Describe the energy balance in humans
Balance between energy intake and energy expenditure
Describe the anabolism of glucose
Glucose enters cell, undergoes glycogenesis forming glycogen in liver and muscle cells
OR undergo lipogenesis and join FA chain
Describe the anabolism of FAs
FAs esterified to triglycerides in adipose tissue
Describe the anabolism of AAs
AAs undergo protein synthesis to form proteins in muscle
Describe the metabolism of glycogen
Glycogen undergoes glycogenesis forming glucose, undergoes glycolysis to pyruvate converted to acetyl-CoA enters TCA
Describe metabolism of triglycerides
Undergo lipolysis forming FAs, undergo B-oxidation to form acetyl-CoA enter TCA
Describe protein metabolism
Proteolysis converts to AAs either directly enter TCA or converted to acetyl-CoA
Describe glycogen stores and their mobilisation
In liver glycogen converted to glucose-6-P which is converted to glucose which can enter brain or back to glucose-6-P and used by muscles to produce lactate
Muscle cells produce glucose 6P then lactate
Describe the cori cycle
Lactate produced in muscle cell converted to pyruvate which can enter gluconeogensis to re-form glucose which can be recycled
Describe lipid stores and mobilisation
Triglyceride stored in adipose broken down to glycerol and FAs
Glycerol undergoes gluconeogenesis forming glucose, enters brain
FAs enter muscle or undergo ketogenesis forming ketone bodies utilised by brain or enter muscle
Describe protein utilisation
Undergo proteolysis produce AAs which can enter TCA, converted to Acetyl-CoA or undergo transamination (amino group moved)
Acetyl-CoA enter TCA or converted to ketone bodies
After transamination form pyruvate either enter TCA or gluconeogenesis
Describe glucose transport
Enters cells via facilitated diffusion by GLUTs
Uptake increased by increasing GLUTs in PM - insulin or exercise
Describe FA transport
Thought to diffuse across PM or may involve FA transporter proteins
How is energy stored in cells?
In chemical bonds
When cell has enough energy available it stores it by adding Pi group to ADP forming ATP