BIOMOLECULES. Biologically Important Molecules Biomolecules are biologically important molecules.
1 3.1 Organic Molecules Organic molecules contain carbon and hydrogen atoms. Four classes of organic...
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Transcript of 1 3.1 Organic Molecules Organic molecules contain carbon and hydrogen atoms. Four classes of organic...
1
3.1 Organic Molecules
• Organic molecules contain carbon and hydrogen atoms.
• Four classes of organic molecules (biomolecules) exist in living organisms: Carbohydrates Lipids Proteins Nucleic Acids
2
The Carbon Skeleton and Functional Groups
• The carbon chain of an organic molecule is called its skeleton or backbone.
• Functional groups are clusters of specific atoms bonded to the carbon skeleton with characteristic structures and functions.
Determine the chemical reactivity and polarity of organic molecules
Table 3.2
4
Biomolecules
• Carbohydrates, lipids, proteins, and nucleic acids are called biomolecules. Usually consist of many repeating units
• Each repeating unit is called a monomer.• A molecule composed of monomers is
called a polymer (many parts).–Example: amino acids (monomer) are
joined together to form a protein (polymer)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 3.3
Biomolecules
PolymerCategory Subunit(s)
PolysaccharideCarbohydrates* Monosaccharide
Lipids
Proteins*
Nucleic acids*
Glycerol and fatty acids Fat
PolypeptideAmino acids
Nucleotide DNA,RNA
*Polymers© The McGraw Hill Companies, Inc./John Thoeming, photographer
6
Synthesis and Degradation
• A dehydration reaction is a chemical reaction in which subunits are joined together by the formation of a covalent bond and water is produced during the reaction. Used to connect monomers together to make
polymers Example: formation of starch (polymer) from glucose
subunits (monomer)
• A hydrolysis reaction is a chemical reaction in which a water molecule is added to break a covalent bond. Used to breakdown polymers into monomers Example: digestion of starch into glucose monomers
monomer monomer
monomer monomer
Dehydrationreaction
H2O
OH H
a. Synthesis of a biomolecule
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+
monomer monomer
Hydrolysisreaction
OH H
b. Degradation of a biomolecule
H2O
monomer monomer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
monomer monomer
monomer monomer
dehydrationreaction
monomer monomer
H2O
OH H
OH H
b. Degradation of a biomolecule
a. Synthesis of a biomolecule
H2O
monomer monomer
hydrationreaction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
10
Synthesis and Degradation
• Enzymes are required for cells to carry out dehydration synthesis and hydrolysis reactions.
An enzyme is a molecule that speeds up a chemical reaction. • Enzymes are not consumed in the reaction.• Enzymes are not changed by the reaction.
3.2 Carbohydrates
• Functions: Energy source Provide building material (structural role)
• Contain carbon, hydrogen and oxygen in a 1:2:1 ratio
• Varieties: monosaccharides, disaccharides, and polysaccharides
12
• A monosaccharide is a single sugar molecule.
• Also called simple sugars
• Have a backbone of 3 to 7 carbon atoms
• Examples: Glucose (blood), fructose (fruit) and galactose
• Hexoses - six carbon atoms
Ribose and deoxyribose (in nucleotides)
• Pentoses – five carbon atoms
Monosaccharides
13
Disaccharides
• A disaccharide contains two monosaccharides joined together by dehydration synthesis.
• Examples: Lactose (milk sugar) is composed of galactose
and glucose.
Sucrose (table sugar) is composed of glucose and fructose.
Maltose is composed of two glucose molecules.
Figure 5.5 Examples of disaccharide synthesis
Polysaccharides
• Polysaccharides Storage:
Starch~ glucose monomers
Plants: plastids Animals: glycogen
• Polysaccharides Structural:
Cellulose~ most abundant organic compound; Chitin~exoskeletons; cell walls of fungi; surgical thread
Lipids 3.3• No polymers; glycerol and fatty acid
• Fats, phospholipids, steroids
• Hydrophobic; H bonds in water exclude fats
• Carboxyl group = fatty acid
• Non-polar C-H bonds in fatty acid ‘tails’
• Ester linkage: 3 fatty acids to 1 glycerol (dehydration formation)
• Triacyglycerol (triglyceride)
• Saturated vs. unsaturated fats; single vs. double bonds
Triglycerides: Long-Term Energy Storage
Also called fats and oils Functions: long-term energy storage and
insulation Consist of one glycerol molecule linked to
three fatty acids by dehydration synthesis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
in
3 H2O
3 H2O
+
CH
H
CH
CH
H
CO
CO
CO
H
H
H H
CCCCC
HHHHH
H
HH
HHH
HHHHHHH
C C
HH
H
HH
HHHHH
CCCCC
CCCCC
HHH
H
H
HHHHH
HCCCCC
HHHHH
HHHHHHH
CCCCCCC
HHHHHH
HHHHH
HC
CCCC
HH H
in
OH
OH
OH HO
HO
HO
H
H
H
H
C
C
C O
H
O C
O
O
C
H
O
C
fat molecule3 watermolecules
3 fatty acidsglycerol
a. Formation of a fat
20
• Fatty acids are either unsaturated or saturated. Unsaturated - one or more double bonds between
carbons• Tend to be liquid at room temperature
– Example: plant oils
Saturated - no double bonds between carbons• Tend to be solid at room temperature
– Examples: butter, lard
Triglycerides: Long-Term Energy Storage
21
• Composed of four fused carbon rings
Various functional groups attached to the carbon skeleton
• Functions: component of animal cell membrane, regulation
• Examples: cholesterol, testosterone, estrogen
• Cholesterol is the precursor molecule for several other steroids.
Steroids: Four Fused Carbon Rings
22
3.4 Proteins
• Proteins are polymers of amino acids linked together by peptide bonds. A peptide bond is a covalent bond between amino
acids.
• Two or more amino acids joined together are called peptides. Long chains of amino acids joined together are
called polypeptides.
• A protein is a polypeptide that has folded into a particular shape and has function.
23
Functions of Proteins
• Metabolism
Most enzymes are proteins that act as catalysts to accelerate chemical reactions within cells.
• Support
Keratin and collagen
• Transport
Hemoglobin and membrane proteins
• Defense
Antibodies
• Regulation
Hormones are regulatory proteins that influence the metabolism of cells.
• Motion
Muscle proteins and microtubules
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
C
H
R
acidicgroup
aminogroup
COOHH2N
R = rest of molecule
Amino Acids: Protein Monomers
• There are 20 different common amino acids.• Amino acids differ by their R groups.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
Sample Amino Acids with Nonpolar (Hydrophobic) R Groups
C C
H O
OC
H
C
O
O
C
H
C
O
O
C C
H O
O
S
C C
O
O
C C
H O
O
C
O
C C
H O
O
C C
H O
O
CO
C C
H O
O
C
O O
C C
H O
O
C
C C
H O
O
C
H
C
O
O
C
H
C
O
O
C
H
C
O
O
C C
H O
O
C C
O
O
CH2
H3N+
H3CCH3
H3N+
(CH2)2
CH3
H3N+
CH2
H3N+
H3N+
CH2
SH OH
CH
H3N+ H3N+ H3N+
CH2(CH2)2
H3N+
CH2
N+H3
OH
H3N+
CH3
NH2
H3N+
H3N+
CH2
CH2
COO-
H3N+CH2
CH2
CH2
H3N+
(CH2)3
NH
N+H2
NH2
H3N+
CH2
NH
N+H
histidine (His)arginine (Arg)aspartic acid (Asp)lysine (Lys)glutamicacid (Glu)
asparagine (Asn) threonine (Thr)
Sample Amino Acids with Polar (Hydrophilic) R Groups
proline (Pro)leucine (Leu)phenylalanine (Phe)methionine (Met)valine (Val)
CHCH3
CH2CH
CH2 H2N+
H2C
glutamine (Gln)
cysteine (Cys) serine (Ser)
tyrosine (Tyr)OH
CH
Sample Amino Acids with Ionized R Groups
CH3
NH2
H
CH2
amino acid
amino groupCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Synthesis and Degradation of a Peptide
dehydration reaction
hydrolysis reaction
water
peptide bond
dipeptideamino acid amino acid
acidic groupamino group
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28
Levels of Protein Structure
• Proteins cannot function properly unless they fold into their proper shape. When a protein loses it proper shape, it said to be
denatured.• Exposure of proteins to certain chemicals, a
change in pH, or high temperature can disrupt protein structure.
• Proteins can have up to four levels of structure: Primary Secondary Tertiary Quaternary
29
Four Levels of Protein Structure
Primary• The sequence of amino acids
Secondary• Characterized by the presence of alpha helices and
beta (pleated) sheets held in place with hydrogen bonds
Tertiary• Final overall three-dimensional shape of a
polypeptide• Stabilized by the presence of hydrophobic
interactions, hydrogen bonding, ionic bonding, and covalent bonding
Quaternary• Consists of more than one polypeptide
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
COO–
hydrogen bond
Primary Structure
This level of structureis determined by thesequence of aminoacids coded by agene that joins toform a polypeptide.
Secondary Structure
Hydrogen bondingbetween amino acidscauses the polypeptideto form an alpha helixor a pleated sheet.
Β (beta) sheet = pleated sheetα alpha) helix
C N
R
C
R
C N
C
R
C
N
C
R
N
C
R
NR
N
C
NR
CH
CH
CH
CH
CH
CH
CH
CH
Tertiary Structure
disulfide bond
Quaternary Structure
This level of structureoccurs when two or morefolded polypeptides interactto perform a biological function.
hydrogen bond
Interactions of amino acid side chains with water, covalent bonding between R groups, and other chemical interactions determine the folded three-dimensional shape of a protein.
peptide bondamino acid
H3N+
C
C
C
CC
C
C
C
C
C
C
C
C
C
C
C
C
C
CC
C
C
R
R
R
R
R
R
R
R
R
O
O
O
O
O
O
O
O
O
O
O
ON
N
N
N
N
N
N
N
N
N
N
C
H H
H
H
H H
HH
H
H
C
O
O
O
O
O
O
O
H
H
H
H
H
H
31
3.5 Nucleic Acids
• Nucleic acids are polymers of nucleotides.
• Two varieties of nucleic acids:
DNA (deoxyribonucleic acid)• Genetic material that stores information for its own
replication and for the sequence of amino acids in proteins.
RNA (ribonucleic acid)• Perform a wide range of functions within cells which
include protein synthesis and regulation of gene expression
32
Structure of a Nucleotide
• Each nucleotide is composed of three parts:
A phosphate group
A pentose sugar
A nitrogen-containing (nitrogenous) base
• There are five types of nucleotides found in nucleic acids. DNA contains adenine, guanine, cytosine, and thymine.
RNA contains adenine, guanine, cytosine, and uracil.
• Nucleotides are joined together by a series of dehydration synthesis reactions to form a linear molecule called a strand.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
S
C
O
Pnitrogen-containingbase
pentose sugar
5'
4' 1'
2'3'
phosphate
Nucleotides
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
S
C
O
–O P O
O
O–
H
O
CC
C C
H
H
H
H
O
CC
C C
H
H
H
HO
N
NH
O N
C CC
C
C
C
C C
HO N
HN
N
N
N
HN N
NCC
C
H
C T UGA
Pnitrogen-containingbase
phosphate
pentose sugar ribose (in RNA)deoxyribose (in DNA)
Nucleotide structurea.
PurinesPyrimidines
OHOHOH
OH OH
HNCH
CH CH
CH
CHHC
CHHN
CH
guanineadenineuracil in RNA
Pyrimidines versus purinesc.
cytosine thymine in DNA
CH2OH CH2OH
NH2
HN
CH3
NH2
H2N
O OO
5'
4' 1'
2'3'
b. Deoxyribose versus ribose
35
Structure of DNA and RNA
The backbone of the nucleic acid strand is composed of alternating sugar-phosphate molecules.
RNA is predominately a single-stranded molecule.
DNA is a double-stranded molecule.
• DNA is composed of two strands held together by hydrogen bonds between the nitrogen-containing bases. The two strands twist around each other to form a double helix.
– Adenine hydrogen bonds with thymine
– Cytosine hydrogen bonds with guanine
• The bonding between the nucleotides in DNA is referred to as complementary base pairing.
36
A Special Nucleotide: ATP
• ATP (adenosine triphosphate) is composed of adenine, ribose, and three phosphates.
• ATP is a high-energy molecule due to the presence of the last two unstable phosphate bonds.
• Hydrolysis of the terminal phosphate bond yields:
The molecule ADP (adenosine diphosphate)
An inorganic phosphate
Energy to do cellular work
• ATP is called the energy currency of the cell.
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ATP
N
NN
N + +PPP P P PN
NN
N ENERGY
phosphatediphosphate
ADP
triphosphate
ATPb.
NH2NH2
H2O
adenosine triphosphate c.a.
adenosineadenosine
c: © Jennifer Loomis / Animals Animals / Earth Scenes