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Flashcards in Biochemistry Deck (556)
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181

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

182

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

183

What is lactose?

Disaccharide of B-D-galactose and B-D-glucose linked through B-1,4

184

What are glycosaminoglycans? (GAGs)

Large, pure carbohydrates that are -ve charged, hydrophilic
Polysaccharides present on animal cell surface and in ECM

185

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)

186

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)

187

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)

188

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)

189

What are proteoglycans?

Heavily glycosylated glycoproteins - core protein with several GAG chains

190

What are the functions of GAGs?

Structural: ECM and BM
Space-filling in cartilage
Modifiers/activators of effector proteins (growth factors, proteases)

191

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

192

What is chondroitin sulphate?

Sulphate GAG composed of N-acetyl-galactosamine and glucuronic acid
Usually forms part of a proteoglycan

193

What is the function of chondroitin sulphate?

Major structural component in cartilage conferring resistance to compression
Dietary supplement for treatment of osteoarthritis

194

What is heparin?

Highly sulphated GAG used as injectable anticoagulant and used for inside of test tubes, renal dialysis machines

195

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

196

Describe the energy balance in humans

Balance between energy intake and energy expenditure

197

Describe the anabolism of glucose

Glucose enters cell, undergoes glycogenesis forming glycogen in liver and muscle cells
OR undergo lipogenesis and join FA chain

198

Describe the anabolism of FAs

FAs esterified to triglycerides in adipose tissue

199

Describe the anabolism of AAs

AAs undergo protein synthesis to form proteins in muscle

200

Describe the metabolism of glycogen

Glycogen undergoes glycogenesis forming glucose, undergoes glycolysis to pyruvate converted to acetyl-CoA enters TCA

201

Describe metabolism of triglycerides

Undergo lipolysis forming FAs, undergo B-oxidation to form acetyl-CoA enter TCA

202

Describe protein metabolism

Proteolysis converts to AAs either directly enter TCA or converted to acetyl-CoA

203

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

204

Describe the cori cycle

Lactate produced in muscle cell converted to pyruvate which can enter gluconeogensis to re-form glucose which can be recycled

205

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

206

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

207

Describe glucose transport

Enters cells via facilitated diffusion by GLUTs
Uptake increased by increasing GLUTs in PM - insulin or exercise

208

Describe FA transport

Thought to diffuse across PM or may involve FA transporter proteins

209

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

210

What are the stages of ATP production?

Digestion
Glycolysis
TCA