Biochemistry Flashcards
Eukaryotic cells
Protista, fungi, plants, animals
10-100μm
Nucleus - spherical, largest organelle, surrounded by double membrane nuclear envelope, contains nucleolus (that synthesizes ribosomal RNA) and genetic material
Chromosome is linear molecule with histone proteins
Plasma membrane - phospholipid bilayer, semi-permeable with receptor proteins
+- cell wall
Cytoplasm - for cellular shape and integrity, has cytoskeletons (for cytokinesis and endocytosis) and membrane-bound organelles (endoplasmic reticulum rough w ribosomes or smooth, golgi apparatus, mitochondria (powerhouse with maternal genetic material, self-replicating), lysosomes and peroxisomes (digestive enzymes, acidic)
Cell division mitosis or meiosis
Prokaryotic cells
Mainly bacteria
1-10μm
No membrane bound organelles
No nucleus, nuclear material lies in cytoplasm
Chromosome usually circular
Can carry plasmids
Most have cell wall
No mitochondria
Cell division by binary fission
Signal transduction
Where external stimulus to cell is converted to specific cellular response eg activation of genes, metabolic alterations, proliferation of cell
Can be ms (ion influx) to days (gene expression)
Then intracellular signal transduction via second messengers
Signalling molecules - hormones, growth factors, cytokines, chemokines, neurotransmitters, extracellular matrix components
Act on cellular receptors - cell surface (endocrine via blood, paracrine to local cells, autocrine to own cell producing hormone) or intracellular
Cell surface receptors
Ion-channel-linked receptors - voltage-gated (Na/Ca/K) or ligand gated (nicotinic acetylcholine, GABA, 5-HT, glycine)
Enzyme-linked receptors - to activate tyrosine protein kinase, receptors for growth factors (tyrosine kinase, tyrosine phosphatase, guanylyl cylase, histidine kinase, serine)
G protein-coupled receptors - to activate G proteins (guanine nucleotide-binding proteins), have 3 subunits α β γ, only in eukaryotes (rhodopsin-like, secretin, metabotropic glutamate, cAMP)
Adrenergic receptors
In G protein-coupled receptor family
Promote glycogenolysis and gluconeogenesis from adipose tissue and liver
α antagonists
β antagonists
α antagonists
For BPH/HTN
α1 eg tamsulosin, prazosin, doxazosin
- activation of phospholipase C, so increasing IP3 and diacylglycerol, to increase intracellular Ca
- drugs -> smooth muscle relaxation (ureter, urethral sphincter, uterus) and smooth muscle contraction of GI tract, vasodilation of arteries and veins, inhibit glycogenolysis and gluconeogenesis
α2 mainly in research
- inactivation of adenylate cyclase leading to decreased intracellular cAMP
β antagonists
β1
- activation of adenylate cyclase, increased intracellular cAMP, activate protein kinase A
- chronotropic and inotrophic effect on heart, renin release, lipolysis in adipose tissue
β2
- smooth muscle relaxation (bronchi, uterus, detrusor, GItract), contracts anal sphincter, vasodilatory
β3
- lipolysis in adipose
eg NON-SELECTIVE propanolol, CARDIOSELECTIVE β1 atenolol, metoprolol, bisoprolol, MIXED α1β1 labetalol carvedilol
α and β agonists
α1 agonist - phenylephrine, noradrenaline
α2 agonist - clonidine
β1 agonist - noradrenaline, isoprenaline, dobutamine
β2 agonist - salbutamol, isoprenaline, terbutaline
Acetylcholine
Neurotransmitter in brain and ANS
Only neurotransmitter at neuromuscular junction
eg nicotinic and muscarinic receptors
Both PREganglionic sympathetic and parasympathetic fibres are cholinergic
All POSTganglionic parasymp fibres are cholinergic
All POSTganglionic symp fibres are adrenergic
Nicotinic receptors
Ionotrophic receptors
Form ligand-gated ion channels in plasma membrane on postsynaptic side of NMJ
No secondary messengers
Muscle type or neuronal type
Stimulation -> excitatory postsynaptic potential in neurones
Agonists - acetylcholine, choline, nicotine, suxamethonium
Antagonists - pancuronium, tubocurarine, atracurium
Muscarinic receptors
G protein-coupled receptors
5 subtypes - M1 exocrine and CNS, M2 heart, M3 blood vessels lungs and salivary glands, M4 CNS
M2 and M4 decrease intracellular cAMP
M1, M3, M5 upregulate phospholipase C and so inositol triphosphate and intracellular Ca
Work to increase exo and endocrine secretions, decrease HR, reduce cardiac contractility, smooth muscle contraction (bronchoconstriction), vasodilation, eye accommodation and pupillary constriction
Agonists - acetylcholine, muscarine, pilocarpine
Antagonists - atropine, scopolamine, ipratropium, tolterodine, oxybutinin
Acetylcholine receptor blocking agents
Non-depolarizing - work by blocking the binding of ACh to receptor - tubocurarine, pancuronium
Depolarizing - by depolarizing plasma membrane of skeletal muscle fibre - suxamethonium
Intracellular receptors
eg cytoplasmic and nuclear receptors
Exclusively intracellular receptors are steroid hormone, thyroid hormone, retinoic acid, vitD3 receptors
Intracellular second messengers
Ca ions
Lipophilic messengers - diacylglycerol, IP3
cAMP - synthesized from ATP by adenylate cyclase, activates protein kinase A
cGMP - synthesized from GTP by guanylate cyclase, activate protein kinase G, relaxes smooth muscle, degraded by phosphodiesterases
NO
NO
= endothelium-derived relaxing factor
- vasodilatation, modulation of hair cycle, penile erection
Biosynthesized from L-arginine -> NO + L-citrulline, catalysed by nitric oxide synthase NOS
3 types of NOS - endothelial (calcium-calmodulin dependent, 10s half life, acts on vascular smooth muscles, expressed by syncytiotrophoblasts), inflammatory (calmodulin INdependent, secreted by bacterial cell wall and neutrophils after activation by TNF or interferonγ), brain
Mechanism of action NO
Stimulate cGMP
Activates protein kinase G
Phosphorylates myosin light chain phosphatase
Inactivates myosin light chain kinase
Dephosphorylates myosin light chain
Smooth muscle relaxation
Carbohydrates
Made of carbon, hydrogen, oxygen only
Can be converted into fat, but fat cannot be converted into glucose
ATP stores energy, can be hydrolysed to release
Monosaccharides - fructose, glucose, galactose
Disaccharides - maltose, sucrose, lactose
Oligosaccharides - ABO blood groups
Polysaccharides - amyolse, glycogen
Glucose
C6H12O6
The ONLY subtance that can undergo anaerobic metabolism
2g/kg/day requirement, brain needs at least 25g/day in starvation or 100g/day normally
Low Km value (= high affinity of transporter protein)
Maltose = 2 units of glucose
Lactose = glucose + galactose (by lactase enzyme)
Sucrose = glucose + fructose (by sucrase enzyme)
Lactate is converted to glucose via Cori cycle
Glucose sources
Glycogen - stored in muscle (if G6PD can’t release into circulation) and liver, stores last 24hrs
Muscle protein conversion
Breakdown of other carbohydrates
Glucose metabolism
Anaerobic
- glycolytic pathway
- in cytosol
- end product is lactate
- produces 2mol ATP per mol glucose
Aerobic
- glucose -> pyruvate via glycolysis
- pyruvate -> acetyl coA via pyruvate dehydrogenase (irreversible)
- acetyl-coA enters tricarboxylic acid cycle -> energy rich molecules then used in oxidative phosphorylation
- yields 36-38mol ATP per mol glucose
- in mitochondria
Glycolysis
Converts glucose to pyruvate, in aerobic and anaerobic conditions
- double phosphorylation
= Embden-Meyerhof pathway
glucose -> glucose-6-phosphate -> fructose-6-phosphate -> F 1,6-biphosophate -> glyceraldehyde 3-P -> 1,3 diphosphoglycerate -> 3-phosphoglycerate -> 2, phosphoglycerate -> phosphoenol pyruvate -> pyruvate -> lactate
TCA pathway
Tricarboxylic acid cycle
= Kreb’s cycle / citric acid cycle
- acetyl coA (2C) + oxaloacetate (4C) -> citrate (6C), using citrate synthase - regulated/inhibited here
- citrate (6C) -> isocitrate (6C), using aconitase
- isocitrate (6C) + NAD+ -> ketoglutarate (5C) + CO2 + NADH + H+, using isocitrate dehydrogenase
- ketoglutarate (5C) + NAD -> succinyl coA (4C) + CO2 + NADH + H+, using ketoglutarate dehydrogenase
- succinyl-coA (4C) + GDP -> succinate (4C) + GTP, using succinyl-coA synthetase
- succinate (4C) + FAD -> fumarate (4C) + FADH2, using succinate dehydrogenase
- fumarate -> malate, using fumarase
- malate (4C) + NAD -> oxaloacetate (4C) + NADH + H+, using malate dehydrogenase
Citrate
Is (isocitrate)
Krebs (ketoglutarate)
Starting (succinylcoA)
Substrate (succinate)
For (fumarate)
Making (malate)
Oxacloacetate
Tisssues that can undergo anaerobic metabolism
RBCs - no intracellular organelle, entirely depends on glucose, CANNOT use fat/ketones/amino acids
Retinal cells
Kidney medulla
Skeletal muscles
Cori cycle
Converts lactate (from anaerobic metabolism) back to glucose
In liver
Important - produces ATP and prevents build up of lactic acid
Features of gestational diabetes
Loss of insulin sensitivity
Hyperglycaemia
Increased plasma fatty acids
Increased plasma ketone bodies
Fetal macrosomia
Increased risk of developing T2DM later
Diagnosis
- fasting glucose of >5.6
OR
- 2hour level >7.8
Triglycerides
Fuel store
Dehydrated
= 1 molecule glycerol, 3 molecules free fatty acid
Stored in adipocytes
Transported by chylomicrons
Fatty acids
β oxidation in mitochondria
Metabolized to acetyl coA
Essential fatty acids - linoleic acid, linolenic acid (both unsaturated)
Phospholipids
Main component of cell membrane
3 groups - lecithin, sphingomyelin, cephalins
Ketone bodies
By-products of fatty acid metabolism (fatty acid -> acetyl coA -> ketone bodies)
Synthesized in liver and kidney
Consist of β-hydroxybutyrate, acetoacetic acid, acetone (excreted in urine and lung)
Fuel for intermediate or prolonged starvation
All (except acetone) can be converted to acetyl coA
Limitations of fat
Not metabolized by brain (except ketone bodies)
Not metabolized anaerobically
Cannot synthesize glucose
Adipose tissue
White - stores energy
Brown - lots of uncoupled mitochondria which do not produce ATP, produces heat
Amino acids
2 functional groups - amine and carboxyl
Acid and base at the same time
Zwitterion = neutral charge amino acid ion (at certain isoelectric point the number of positive and negative charges are equal).
- +ve charge from protonated amine group
- -ve charge from deprotonated carboxyl group
Can be precursors, eg tryptophan -> serotonin, glycine -> porphyrins, arginine -> NO, tyrosine -> L-DOPA -> dopamine and noradrenaline
Subclasses of amino acids
Total 20 in humans, 10 are essential
- lysine
- leucine
- isoleucine
- valine
- methionine
- phenalynine
- tryptophan
- threonine
(arginine + histidine are essential dependent on age/health)
Grouped into acidic, basic, aromatic, sulphydryl, imino, hydroxyl, aliphatic
Detoxification
1st
Amino acid -> glutamic acid -> carbamyl phosphate
Then urea cycle in liver:
1. mitochondria
Carbamyl phosphate + ornithine -> citrulline -> arginosuccinate + aspartate
2. cytoplasm
Arginosuccinate -> arginine -> urea + ornithine
Proteins
Polymerized amino acids, linked by peptide bonds
3 classes - globular (soluble, form enzymes), fibrous (structural), membrane (receptors)
Primary structure - amino acid sequence with peptide bonds
Secondary structure - 3D form of primary structure, held by hydrogen bonds
Tertiary structure - overall shape of single protein molecule, held by disulphide bonds, controls basic function of protein
Quaternary structure - arrangement of multiple folded protein molecules
Haemoglobin
1 haem ring + 4 globin rings (2α, β, γ, or δ subunits)
- if α then chromosome 16 (short arm), if β then chromosome 11 (short arm)
- synthesized in mitochrondira and cytosol of immature RBCs
- also found in non-erythroid cells eg dopaminergic neurones in substantia nigra, macrophages, alveolar cells, kidney mesangial cells
- haem is metabolised to bilirubin and cytosol of immature RBCs
Subtypes of Hb
Embryo - Gower 1, Gower 2, Portland
Fetus - HbF (α2γ2) majority Hb by 12 weeks, 95% by birth then decline by 6months
Adult - HbA (α2β2), HbA2 (α2δ2)(3%), HbF(α2γ2)
Variant - HbS (sickle cell), HbC , HbH, Barts, HbE
Collagen
Secreted by fibroblasts and osteoblasts, from pro-collagen
4 subtypes
- type 1 (bone/dermis/tendon) - makes up 50% of total body protein
- type 2 (cartilage)
- type 3 (fetal/cardiac/scar/synovium)
- type 4 (basement membrane)
Classes of hormone
Endocrine/exocrine
Amine-derived - catecholamines, thyroxine
Peptide-derived - vasopressin, insulin, LH, FSH, TSH
Phospholipid-derived (steroids) - testosterone, cortisol
Cholesterol
Ring-based structure
27 C atoms
Transported by HDL and LDL (lipoproteins)
Synthesized in endoplasmic reticulum via HMG-CoA reductase pathway
Sourced from acetyl-CoA, plasma membrane cholesterol, plasma lipoproteins, intracellular lipid droplets
Steroids
4 rings - 3 have 6 C atoms, 1 has 5 C atoms
Steroid receptors are a subclass of nuclear receptors, associated with HSP (heat shock protein)
Work to increase gene transcription
Hydrophobic
5 groups:
Corticosteroids
- mineralcorticoids (aldosterone)
- glucocorticoids (cortisol)
- androgen (DHEA)
Gonadal
- progestogens
- oestrogens
- androgens (testosterone)
Steroid synthesis
Cholesterol (C27) -> progestin (C21) -> androgen (C19) -> oestrogen (C18)
Using enzymes cytochrome p450 complex, and hydroxysteroid dehydrogenase
Rate limiting step is conversion of cholesterol to progestin, using enzyme cytochrome p450CSCC (cholesterol side chain cleavage) which lives in inner mitochondria
Cholesterol cannot transverse aqueous space between mitochondrial membranes unaided, needs STAR (steroidogenesis acute regulatory, only in ovaries or testes) protein and PBRs (peripheral benzodiazepine receptors)
Cytochrome p450 complex
Variety of enzymes, including:
17-hydroxylase
- catalyses pregnenolone -> 17α-hydroxy-pregnenolone -> DHEA
- and progesterone -> 17α-hydroxy-progesterone -> androstenedione
21-hydroxylase
- catalyses progesterone -> corticosterone
- and 17α-hydroxy-progesterone -> cortisol
Hydroxysteroid dehydrogenase
HSD, 2 types:
3β-HSD
- converts weak to strong steroid
- catalyses pregnenolone -> pregnanedione, and 17α-hydroxy-pregnenolone -> 17α-hydroxy-progesterone, and DHEA -> androstenedione
17β-HSD
- catalyses androstenedione -> testosterone, and oestrone -> oestradiol
Oestrogens
Phenol aromatic compounds
18 C atoms
p450 aromatase catalyses testosterone -> oestradiol and androstenedione -> oestrone
Gonadal cells
Leydig cells produce testosterone, have 17β-HSD
Theca cells produce androgens, does not have 17β-HSD
Granulosa cells produce oestradiol, have 17β-HSD
Luteal cells produce progesterone and oestradiol
Lipoid congenital adrenal hyperplasia
Autosomal recessive condition
Due to mutations of genes for enzymes mediating the production of cortisol from cholesterol by adrenal glands
- defect in 21-hydroxylase (95%), STAR protein, or cytochrome P450CSCC
- so failure of steroid production and accumulation of large lipid droplets (cholesterol ester) in adrenal cortex
(insufficient cortisol -> increased ACTH -> hyperplasia of adrenal cortex)
Presents as ambiguous genitalia, natriuresis, precocious puberty/failure of puberty, infertility due to anovulation, virilisation, hypertension
Prostaglandins
Produced by all nucleated cells except lymphocytes
Hydrophilic
Vasomotor functions
- vasoconstrictor - thromboxane, leukotriene
- vasodilator - PGD, PGE2, PGF2, prostacyclin
Non-vasomotor functions
- PGE2 - pyrogenic, hyperalgesia, uterine contractions, increased gastric mucus, GI smooth muscle contraction or relaxation (dependent on receptor), bronchoconstriction or dilation (receptor)
- PGF2 - uterine constriction, bronchoconstriction
- prostacyclin - inhibition of platelet aggregation, bronchodilation
Prostaglandin synthesis pathway
Arachidonic acid (20C)
- cyclo-oxygenase pathway -> prostaglandin H2 -> thromboxane A2, PGE2 and PGF2, prostacyclin
- lipoxygenase pathway -> leukotriene
Prostaglandin dehydrogenase
Metabolises prostaglandins
Found in lungs, ovary, testes, placenta
Prostaglandin receptors
G-protein receptors
Seven-transmembrane domain
EP receptor (PGE2)
FP receptor (PGF2)
Clinical applications for prostaglandins
Induction of labour - PGE2, PGF2
Prevent closure of patent ductus arteriosus - PGE2
Treatment of Raynaud’s, glaucoma, limb ischaemia, erectile dysfunction, peptic ulcers
Starvation
Obligate need to generate glucose to sustain cerebral energy metabolism (brain needs at least 25g/day)
- by mobilizing glycogen stores and hepatic gluconeogenesis
Initially
- brain, RBCs, WBCs, renal medulla can only use glucose for their metabolism
12hours
- fall in insulin, rise in glucagon, glycogenolysis in liver, muscle glycogen -> lactate then conversion in Cori’s cycle to glucose
24hours
- glycogen stores depleted, gluconeogenesis with protein catabolism of skeletal muscle
48hours
- TAG (fat) oxidation by lipolysis, releases glycerol which can be converted to glucose and fatty acids (FAs then converted to ketones in liver)
2-3 weeks
- CNS adapts to using ketones as primary fuel source to reduce muscle breakdown
Serum progesterone levels in diagnosis of pregnancy
NICE does NOT suggest use of serum progesterone measurements as an adjunct to diagnose either viable intrauterine pregnancy or ectopic pregnancy
RCOG suggest <20nmol/l strongly suggestive non-viable pregnancy
>60nmol/l suggestive intrauterine pregnancy
Cell organelles
Mitochondria - energy (ATP) production
Golgi Apparatus - storing, packaging and modification of proteins
Endoplasmic Reticulum
- Rough: Protein assembly, folding & quality control
- Smooth: Folding of proteins and transport in vesicles, and synthesis of lipids & role in gluconeogenesis via G6DP
Nucleus - contains chromosomes, cell command centre via regulation of gene expression
Ribosome - translation of mRNA into protein
Vitamin K
Fat soluble vitamin that is stored in the liver and adipose tissues. Other fat soluble vitamins are A, D and E.
It is essential for the synthesis of:
- Clotting factors (X)10,(IX) 9, 7(VII), 2 (II) = 1972 (1o, 9,7, 2)
- Proteins C, S and Z
- Osteocalcin and GLA proteins
Organelles function
Nucleus: DNA Storage
Mitochondria: Energy production
Smooth Endoplasmic Reticulum (SER): Lipid production; Detoxification
Rough Endoplasmic Reticulum (RER): Protein production; in particular for export out of the cell
Golgi apparatus: Protein modification and export
Peroxisome: Lipid Destruction; contains oxidative enzymes
Lysosome: Protein destruction
