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Transcript
The Chemical Building
Blocks of Life
Chapter 3
Carbon
• Framework of biological molecules
consists primarily of carbon bonded to
– Carbon
– O, N, S, P or H
• Can form up to 4 covalent bonds
• Hydrocarbons – molecule consisting only
of carbon and hydrogen
– Nonpolar
– Functional groups add chemical properties
2
– Functional groups - The groups of atoms that
usually participate in chemical reactions.
– Two common examples are
• Hydroxyl groups (-OH)
• Carboxyl groups (C=O)
3
4
Macromolecules
• Polymer – built by linking monomers
• Monomer – small, similar chemical subunits
5
• Dehydration synthesis
– Formation of large molecules by the removal of water
– Monomers are joined to form polymers, endergonic
• Hydrolysis
– Breakdown of large molecules by the addition of
water
– Polymers are broken down to monomers, exergonic
6
Carbohydrates
• Molecules with a 1:2:1 ratio of carbon,
hydrogen, oxygen
• Empirical formula (CH2O)n
• C—H covalent bonds hold much energy
– Carbohydrates are good energy storage
molecules
– Examples: sugars, starch, glucose
7
Monosaccharides
• Simplest carbohydrate
• 6 carbon sugars play important roles (energy
storage)
• Glucose C6H12O6
• Fructose – fruit sugar
• Galactose – milk sugar
• Enzymes that act on different sugars can
distinguish structural and stereoisomers of this
basic six-carbon skeleton (Taste buds can
detect fructose tastes sweeter than glucose)
8
9
10
Disaccharides
• 2 monosaccharides linked together by
dehydration synthesis
• Used for sugar transport or energy storage
• Examples: sucrose, lactose, maltose
11
Polysaccharides
• Long chains of monosaccharides
– Linked through dehydration synthesis
• Energy storage
– Plants use starch – Ex?
– Animals use glycogen (stored in liver and
muscles)
• Structural support
– Plants use cellulose (is not easily broken down)
cows have bacteria that allow this.
– Arthropods and fungi use chitin – tough resistant
12
surface material
13
14
Nucleic acids
• Polymer – nucleic acids
• Monomers – nucleotides
– sugar + phosphate + nitrogenous base
– sugar is deoxyribose in DNA or ribose in RNA
– Nitrogenous bases include
• Purines: adenine and guanine
• Pyrimidines: thymine, cytosine, uracil
– Nucleotides connected by phosphodiester
bonds
15
16
17
Deoxyribonucleic acid (DNA)
• Encodes information for amino acid
sequence of proteins
– Sequence of bases
• Double helix – 2 polynucleotide strands
connected by hydrogen bonds
– Base-pairing rules
• A with T (or U in RNA) – 2 H bonds
• C with G – 3 H bonds
18
19
Ribonucleic acid (RNA)
• RNA similar to DNA except
– Contains ribose instead of deoxyribose
– Contains uracil instead of thymine
• Single polynucleotide strand
• RNA uses information in DNA to specify
sequence of amino acids in proteins
20
21
Other nucleotides
• ATP adenosine triphosphate
– Primary energy currency of the cell
• NAD+ and FAD+
– Electron carriers for many cellular reactions
22
Proteins
Protein functions include:
1. Enzyme catalysis – facilitate chemical reactions
2. Defense – recognizes foreign microbes and cancer
cells.
3. Transport – ex. hemoglobin
4. Support – hair, collagen
5. Motion – actin and myosin in muscle contraction
6. Regulation – hormones, receptors
7. Storage – calcium and iron bind to proteins
23
• Proteins are polymers
– Composed of 1 or more long, unbranched
chains
– Each chain is a polypeptide
• Amino acids are monomers
• Amino acid structure
– Central carbon atom
– Amino group
– Carboxyl group
– Single hydrogen
– Variable R group
24
25
• Amino acids joined by dehydration
synthesis
– Peptide bond
26
4 Levels of structure
• The shape of a protein determines its
function
1.Primary structure – sequence of amino acids
2.Secondary structure – interaction of groups
in the peptide backbone forming hydrogen
bonds
 a helix – coiled in a spiral
 b sheet – planar structure
27
4 Levels of structure
3. Tertiary structure – Three dimensional folding.
– Stabilized by a number of forces including H
bonds
4. Quaternary structure – arrangement of
individual chains (subunits) in a functional
protein with 2 or more polypeptide chains
A protein must be in its quaternary structure to
be functional!!!!
28
29
Chaperones
• Once thought newly made proteins folded
spontaneously
• Chaperone proteins help protein fold
correctly
• Deficiencies in chaperone proteins
implicated in certain diseases
– Cystic fibrosis
• In some individuals, protein appears to have
correct amino acid sequence but fails to fold.
(mutation) Results in thicker than normal mucus –
breathing and digestive problems.
30
31
Denaturation
• Protein loses
structure and function
• Due to environmental
conditions
– pH
– Temperature
– Ionic concentration of
solution
– Ex. ?
32
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33
Lipids
• Loosely defined group of molecules with
one main chemical characteristic
– They are insoluble in water
• High proportion of nonpolar C—H bonds
causes the molecule to be hydrophobic
• Fats, oils, waxes, and even some vitamins
34
Fats
• Triglycerides
– Composed of 1 glycerol and 3 fatty acids
• Fatty acids
– Chain length varies (2-14 C) – bonds of fat yield long
term energy storage.
– Saturated – no double bonds between carbon atoms
• Higher melting point, animal origin
– Unsaturated – 1 or more double bonds
• Low melting point, plant origin
– Trans fats produced industrially (hydrogenated) –
linked to increased risk of heart disease (high levels
of LDL, “bad cholesterol”)
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Phospholipids
• Composed of
– Glycerol
– 2 fatty acids – nonpolar “tails”
– A phosphate group – polar “head”
• Form all biological membranes –
phospholipid bilayer of cell membranes
37
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• Phospholipid bilayer – more complicated
structure where 2 layers form
– Hydrophilic heads point outward
– Hydrophobic tails point inward toward each
other
39
Steroids: Example is cholesterol
Function = chemical messengers
(hormones) – Ex. testosterone and
estrogen.
40