01 A sejtek felépítése és anyagcseréje
2014.04.09
Cells: chemicals, structure, metabolism
Elements
Carbon:
• Can join to each other: chains, rings
• 4 strong covalent bonds (saturated, unsaturated)
Oxygen: in organic molecules
Hydrogen: in organic molecules
Nitrogen: proteins, nucleic acids, ATP
Sulphur: proteins
Sodium: for nerve working
Potassium: for nerve working
Magnesium: chlorophyll
Chlorine: for nerve working
Iron: haemoglobin
Silicon: in seaweeds
Compounds
• Water
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
Water
Water content in cells: 60-80%
Important properties:
• Solvent
• Takes part in reactions
• Carries by diffusion
• Takes part in thermoregulation
Diffusion
Passive transport
Osmosis
• passage of water molecules from a dilute solution into a more concentrated solution through a partially permeable membrane
• „Diffusion of water”:
• moves from „high water concentration”
to the „low water concentration”
to the „low water concentration”
Colloids
• Size of particles: 1-500 nm
• Opalescent (Faraday-Tyndall effect)
• Surface area/volume ratio: maximal (materials can be adsorbed on it)
Coagulation
• Colloidic particles stick closely together: became insoluble
• Reversible: can be reversed (e.g. by salt)
• Irreversible: cannot be reversed (e.g. heating, heavy metal solutions, strong acids and alkalines)
Carbohydrates
Monosaccharides: one sugar unit, sweet, soluble in water
• Aldose (aldóz): aldehidcsoport, ketose (ketóz): ketocsoport
• Triose (trióz): 3 szénatom
• Pentose (pentóz): 5 szénatom
• Hexose (Hexóz): 6 szénatom
Trioses
• Glycerinaldehyd (glicerinaldehid)
Pentoses
• Ribose (ribóz)
• 2-deoxyribose (2-dezoxiribóz)
Hexoses
• Glucose (szőlőcukor)
• Fructose (gyümölcscukor): ketóz!
• Galactose (galaktóz)
Disaccharides
2 monosaccharides linked, sweet, soluble in water
• Saccharose (répacukor): α-glucose + β-fructose
• Lactose (tejcukor): β-galactose + β-glucose
• Maltose: α-glucose + α-glucose
• Cellobiose: β-glucose + β-glucose
Polysaccharides
• Glucose-based macromolecules
• Are not sweet, are insoluble in water
Cellulose (β-glucoses): plant cell wall
Starch (α-glucoses): plant carbohydrate reserve
• Amylose: soluble (blue reaction with iodine)
• Amylopectin: insoluble, wall of the starch grains
Glycogen: animal carbohydrate reserve
Lipids
Nonpolar molecules
Insoluble in water, soluble in oil, gasoline
Main groups:
• Triglycerides
• Phospholipids
• Carotenoids
• Steroids
Triglycerides
Glycerol + fatty acids
Saturated fatty acids: stearic and palmitic acid (C17H35-COOH), (C15H31-COOH)
Unsaturated fatty acid: oleic acid (C17H33-COOH
Fats: contain mainly saturated acids (solid at room temperature, animal fats)
Oils: contain mainly unsaturated acids (liquid at room temperature, plant oils)
Role:
• Energy store
• Insulator
• Mechanical protector
• Vitamin store (ADEK)
Phospholipids
• Bonded to glycerol: 2 nonpolar fatty acids and 1 polar group
• A nonpolar (hydrophobic) and a polar (hydrophilic) part: form bilayers (membranes) in water
Carotenoids : long molecules with double bonds: can be induced by the light
• Carotene (carrot)
• Lycopene (tomato)
• Xanthophyll (leaves)
• Vitamin A (eyesight, skin)
Steroids
• Cholesterol: in membranes
• Vitamin D: (ergosterol + UV light) we need it for healthy bones
• Bile acids: emulgeate fats
• Hormones: cortison, estrogen, testosteron, progesteron
Proteins
• Are made of amino acids (p.26)
• Amino acids are bonded with peptide bonds
•
Structure
Primary structure: sequence of amino acids: alanine – arginine – histidine
Secondary structure: shape of the amino acid chain:
• α-helix: twisted chain
• β-pleated sheet: parallel chains
Tertiary structure: higher shape of the chain
Stabilized by covalent, Hydrogen- and Van der Waals-bonds
• Globular: spherical
• Fibrous: line
Quaternary structure: 1 protein – more than 1 polypeptide chains: related position of chains to each other
Features
Denaturation: protein is irreversibly destroyed
Coagulation: Colloidic particles stick closely together: became insoluble (reversible – irreversible)
Dangerous: conformation of the chain changes
Heating, changing of pH, mechanical effects, heavy metal ions
Functions of proteins
• Structure: keratin, collagen
• Transport: haemoglobin
• Moving: muscle proteins
• Enzymes
• Protection: globulines
•
Nucleotides
Components:
Sugar (ribose, 2-deoxyribose)
Phosphate group
Nitrogen-containing base
• Purines: adenine, guanine
• Pirimidines: cytosine, thymine, uracile
Adenosine triphosphate
• ATP = ADP + Pi + energy (30 kJ/mol)
• It can store and release energy
Nicotinamide adenine dinucleotide
• NAD: carries H at the break-down (energy-releasing) processes
• NADP (nicotinamide adenine dinucleotide phosphate): carries H at the build-up processes
• NAD(P) + 2H = NAD(P)H + H+
• 2e- and 1p+ are carried on the molecule, 1 p+ near this
Coenzyme A
• Acethyl group (CH3CO-) is carried by it
Deoxyribonucleic acid (DNA)
• Pentose: deoxyribose
• Base: adenine, guanine, cytosine, thymine
• Paired parallel α-helix
• Chain-stabilizer bonds: A-(2 H-bonds)-T, G-(3 H-bonds)-C
• Can be copied perfectly: carries the genetic information
Ribonucleic acid (RNA)
• Pentose:ribose
• Base: adenine, guanine, cytosine, uracile
• Single α-helix
• Chain-stabilizer bonds: A-(2 H-bonds)-U, G-(3 H-bonds)-C
Types of RNA:
• Messenger RNA: a copy of the nuclear DNA, carries information to the ribosomes
• Transfer RNA: carries amino-acids to the ribosomes
• Ribosomal RNA: builds up the ribosomes (protein synthesis occurs here)
THE CELL
It is the smallest independent unit of life
All organisms are made up of cell(s)
Prokaryotes („before the nucleus”):
· DNA is ring-shaped, is not separated by nuclear membrane
· Cytoplasm is not divided by endoplasmatic membrane
· Diameter: 0,1-10 μm
Eukaryotic cell („true nucleus”): nucleus is surrounded by nuclear membrane
· Diameter: 10-100 μm
· Organelles (visible by light microscope): Nucleus, cell membrane, cell wall, chloroplast, mitochondria, chloroplast, starch grains, Golgi apparatus, sometimes chromosomes
· Organelles (visible by electron microscope): Endoplasmic reticulum, lysosomes, ribosomes, cytoskeleton
CELL ORGANELLES:
Cytoplasm: jelly
· Water (80%)
· Cytoskeleton: protein filaments (move molecules and organelles, gives support to the cell)
· RNA
· ions
Nucleus
· Is surrounded by nuclear envelope (membrane)
· Nucleolus: synthetizes RNA, builds up ribosomes
· Nuclear sap (water, ions, molecules)
· Chromatin: nucleosomes (DNA and histon proteins) (euchromatin: light – heterochromatin: dark /packed DNA/)
MEMBRANES:
Cell membrane
Borders and connects
Structure:
· Double layer of phospholipid molecules
· Proteins: peripheral, integral (pores, transport proteins)
· Carbohydrate chains (bonded to proteins): receptor molecules (marks)
Endoplasmic reticulum
· Complex tunnel system
· Joins to the nuclear envelope
· Rough ER: ribosomes (synthesis of protein molecules)
· Smooth ER: no ribosomes (synthesis of steroids and other substances, detoxication)
Golgi apparatus:
· Flattened cavities and vesicles
· Modifies, packages and in vesicles carries substances synthetised by ER
Lysosomes:
· Small vesicles with digestive enzymes
Nuclear envelop
· Two parallel membranes with pores
· Surrounds the nucleus, it is connected with ER
OTHER CELL ORGANELLES:
Mitochondria
· Size: as a bacterium
· Ring-shaped DNA
· Outer membrane: smooth
· Inner membrane: folded, large surface
· Function: synthesis of ATP (inner membrane) – „power station of the cell”
Chloroplast
· Size: as a bacterium
· Ring-shaped DNA
· Outer membrane: smooth
· Inner membrane: granum (small column built up of small membrane discs)
· Function: molecular processes of photosynthesis
METABOLISM
Metabolism = getting up, transforming and getting rid of materials
ENZYMES
Biochemical reactions in cells: must be rapid at low temperature
Enzymes: biological catalysts
Two types:
· Breakers: break down molecules
· Builders: build up molecules
How an enzyme works:
· Enzymes: proteins (long amino-acid chains)
· Active site: special shape
· Substrate: substance which fits into active site
Properties of enzymes:
· They are proteins
· Each enzyme controls one reaction (they are SPECIFIC)
· They can be used again
· They are affected by temperature
· They are affected by pH
Enzymes in digestion:
· Large molecules can not get through the gut wall
· CARBOHYDRASE: breaks down carbohydrate (e.g. starch)
· PROTEASE: breaks down protein
· CATALASE: breaks down hydrogen-peroxide (poisonous product of reactions) to oxygen and water (It is the fastest enzyme!)
· AMYLASE: a special carbohydrase in saliva. Breaks down starch to sugar
· LIPASE: breaks down fats
Hotting up
· At high temperature the shape of protein changes:
· Substrate can not fit into the active site
· Enzyme is DENATURED
Enzymes and pH
· Many enzymes work best in neutral conditions
· These enzymes are denatured in very acid or alkaline conditions
· PEPSIN works best in very acid conditions in stomach
Active transport
· Uptake of particles against a concentration gradient.
· It needs energy.
· A carrier protein takes up particles to the other side
· Endocytosis: cell membrane surrounds a piece of material bringing into the cell within a vesicle
· Exocytosis: vesicle membrane fuses with the cell membrane (kicks out the waste material)
METABOLISM (anyagcsere)
· Katabolism: breaking down large molecules to smaller ones, releasing energy
· Anabolism: building up large molecules from smaller ones, using energy
Building up
Autotroph: uses inorganic substances
· Photosynthesis: uses energy of light
· Chemosynthesis: releases energy from inorganic compound oxidation
Heterotroph: uses organic compounds
Photosynthesis
i. Light-dependent reaction: Releasing energy of light
Pigments: chlorophyll (a, b), carotene, xanthophyll
ii. Light-independent reaction (Calvin cycle): absorbing CO2, synthesis of glycose
Biological oxidation (aerob, with O2)
Glycolysis: glycose - - pyruvate (piroszőlősav) + ATP (cytoplasm)
Pyruvate oxidation: pyruvate - - acetyl CoA
(Szentgyörgyi) – Krebs cycle (citromsavciklus): carbon oxidation to CO2, ATP, NADH+H+ synthesis (mitochondria matrix)
Electron transport chain (terminális oxidáció): electron transpor to ATP synthesis
(using electrons from NADH) (mitochondria inner membrane)
1 mol glucose -------------- 38 mol ATP!!!
Fermentation (anaerob, without O2)
1 mol glycose ------ 2 mol ATP!!!
Alcoholic fermentation: pyruvate ---- ethanol + CO2
Lactic acid fermentation : pyruvate ----- lactic acid