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Molecular Components of Cells
Chapter 3 Molecular Components of Cells
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Molecular Components of Cells
Chemical composition C, H, N, O and small amount of other elements Molecular building blocks Lipids Carbohydrates Proteins Nucleic acid DNA (deoxyribonucleic acid) RNA (ribonucleic acid)
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Atoms, Ions, and Molecules
Smallest piece of an recognizable element Nucleus (proton + neutron) + electron Same number of protons and electrons : no charge Biologically important atoms: C, H, O, N : > 99% of cell mass S, P, Na, K, Ca, Cl Ions Electrically charged atoms Biological importance: electrical impulse, ion balance Ca2+, Na+, K+, Cl- Molecules Generated from chemical bonding of atoms
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Energetics and Carbon Flow
Figure: 02-08 Caption: Metabolic options for obtaining energy. The organic and inorganic chemicals listed here are just a few of the many different chemicals used by various chemotrophic organisms. Oxidation of the organic or inorganic chemicals yields ATP in chemotrophic organisms while conversion of solar energy to chemical energy (again, in the form of ATP) occurs in phototrophic organisms.
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Figure: 05-23a Caption: Energetics and carbon flow in (a) chemoorganotrophic respiratory metabolism. Note the importance of electron transport leading to proton motive force formation.
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Figure: 05-23b Caption: Energetics and carbon flow in (b) chemolithotrophic metabolism. Note the importance of electron transport leading to proton motive force formation.
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Figure: 05-23c Caption: Energetics and carbon flow in (c) phototrophic metabolism. Note how in phototrophic metabolism carbon for biosynthesis can come from CO2 (photoautotrophy) or organic compounds (photoheterotrophy). Note also the importance of electron transport leading to proton motive force formation.
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Subunits of Biological Molecules
Class of Molecules Examples Repeating Unit Lipid Fats, oils Glycerol, fatty acid Carbohydrate Sugars, starch, cellulose Simple sugars Nucleic acid DNA, RNA Nucleotide Proteins Enzymes Amino acids
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Chemical composition of living cells
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Different kinds of molecules
Table. Overall Macromolecular Composition of an Average Cell of E. coli Macromolecules Percentage of total dry weight Different kinds of molecules Protein 55.0 1050 RNA 20.5 rRNA 16.7 3 tRNA 3.0 60 mRNA 0.8 400 DNA 3.1 1 Lipid 9.1 4 Lipopolysaccharide 3.4 Peptidoglycan 2.5 Glycogen Soluble pool 3.9
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Media elemental composition
Chemical forms %(Dry cell Wt) Carbon Glc, malate, AA, acetate, YE, peptone 50 Nitrogen N2, Inorganic & organic nitrogen cpds 14 Oxygen O2, H2O, organic cpds 20 Hydrogen H2O, organic cpds 8 Phosphorous PO4-3 3 Sulfur H2S, SO4-2 1 Potassium K salts Magnesium Mg2+ salts 0.5 Sodium NaCl and Na+ salts Calcium CaSO4 and Ca2+ salts Iron FeS or Fe2+ and Fe3+ salts 0.2
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Defined vs. Complex media
Complex media for E.coli MM media for B. megatrium Component Amount Function of component sucrose 10.0 g C and energy source K2HPO4 2.5 g pH buffer; P and K source KH2PO4 (NH4)2HPO4 1.0 g pH buffer; N and P source MgSO4 7H2O 0.20 g S and Mg++ source FeSO4 7H2O 0.01 g Fe++ source MnSO4 7H2O 0.007 g Mn++ Source water 985 ml pH 7.0 Component Amount Function Glucose 15g Yeast Extract 5 g Peptone KH2PO4 2g Distilled H2O 1000mL pH 7
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Comparison of amino acid compositions in cell
Various mammalian cell Amino Acids (1997) 13:
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1 Lipids 2 Carbohydrates 3 Proteins 4 Nucleic acids
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Lipids Characteristics Functions Water insolubility Diverse structures
Energy storage : high energy C-H, C-C bonds Fats : fatty acid + glycerol Components of biological membrane Phospholipids Cholesterol Signals Steroid hormones Enzyme cofactors Vitamins
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Fats Structure Function Other names
Glycerol + 3 fatty acids linked by ester linkage Function Energy storage Other names Triacylglycerol, triglycerides, neutral fats Oil : liquid at room temperature
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Fatty Acids Saturated fatty acids Unsaturated fatty acids
Tight packing High melting point Solid at room temperature Unsaturated fatty acids More than one cis-double bond Low melting point Lliquid at room temperature
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Phospholipids Structure Function Glycerol backbone
two fatty acids (hydrophobic)+ phosphate (hydrophilic) Additional small polar molecules bound to phosphate group Function Major component of cellular membrane
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Sterols Structure Cholesterol Cyclic hydrocarbon compounds
Planar and rigid rings 3 with C6 and 1 with C5 Cholesterol Component of animal cell membranes Decrease membrane fluidity Starting material for steroid hormones and bile synthesis
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Vitamins Vitamin A, D, E, K Vitamin A (retinol) Vitamin D2
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1 Lipids 2 Carbohydrates Proteins 3 4 Nucleic acids
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Carbohydrates Structure Classes of carbohydrates
Polyhydroxy aldehydes or ketones C:H:O = 1:2:1 Classes of carbohydrates Simple sugars (monosaccharide) 3 to 7 carbons Aldose: aldehyde group, e.g) glucose, galactose Ketose: ketone , e.g) fructose Disaccharides Simple sugars linked by glycosidic bond Sucrose: glucose (a1↔2b) fructose Lactose : galactose (b14) glucose Maltose : glucose (a1 4) glucose Oligosaccharides Polysaccharides
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Cyclic Structure of Monosaccharides
Formation of cyclic structure Monosaccharides with 5 or more carbons
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Carbohydrates OH 1 2 1 CH2OH Glc (a1↔2b)Fru Gal (b14)Glc
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Carbohydrates Polysaccharide Starch, Glycogen, cellulose from glucose
Agar, carrageenan (thickener) Cellulose b-1,4 glycosidic linkage Starch, glycogen Starch Glycogen a-1,6 glycosidic linkage a-1,4 glycosidic linkage
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Roles of Carbohydrates I
Carbohydrates in energy metabolism Plant Glucose synthesis by photosynthesis 6CO2 + 6H2O + energy C6H12O6 + 6O2 Starch for energy storage cellulose for structural compound Animals Intake glucose from food Glycogen for energy storage
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Roles of Carbohydrates II
Carbohydrates in molecular recognition Cellular recognition, cell signaling, cell adhesion e.g. blood typing : sugar chains in the membrane of RBC
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1 Lipids 2 Carbphydrates Proteins 3 3 4 Nucleic acids
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Proteins Roles of proteins Most of the cellular functions
Enzymes : chemical reactions Receptors : signal transduction Antibody : recognition of foreign molecules and trigger immune responses Transporters : e.g. hemoglobin for oxygen Structural proteins : keratin (hair and nails), actin and myosin (muscle) Diversity of organism Due to diversity in organization of proteins within an organism
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Proteins Amino acids Polypeptide Three-dimensional structure
Building blocks of proteins Hydrophilic backbone + 20 side chains Polypeptide Amino acid chains linked by peptide bond Three-dimensional structure Determines protein function Determined by amino acid sequence
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1 Lipids 2 Carbphydrates 3 Proteins 4 Nucleic acids 4
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Nucleic acids Nucleotides Terminology Building blocks of nucleic acids
2’(deoxy)ribose + phosphate group + 4 bases Bases: adenine (A), guanine (G), cytosine (C), thymine (T) Terminology Base Nucleoside : sugar + base Nucleotide : sugar + base + phosphate o o
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Primary Structure : Nucleotides
Base Nucleoside Nucleotide Adenine Guanine Cytosine Thymine (D) Uracil (R) Adenosine Guanosine Cytidine Thymidine Uridine Adenylate Guanylate Cytidylate Thymidylate Uridylate Purine Pyrimidine H 2’-Deoxyribose RNA DNA
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Nucleotide Chains Linkage of 5’ carbon to 3’ carbon through phosphodiester bond
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Base Pairing C=G, T=A : hydrogen bonding Complementary base pairs
Antipararallel strand in DNA molecule
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DNA Double Helix
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Chromosome Tightly packed complex of DNA and histone proteins
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DNA Replication Synthesis of a complementary strand using the other strand as a template DNA polymerase
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Expression of Genetic Information
Replication DNA Transcription mRNA Translation Protein
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Differences Between DNA and RNA
Properties DNA RNA Chemical Deoxyribose ribose Tymine Uracil Structural Double strand Single strand
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Balanced growth Monod Equation Substrate-limited growth
Exponential phase in Semi-log plot: slope =
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