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Chapter 3 . Biological Molecules. Why Is Carbon So Important in Biological Molecules?. Organic/inorganic molecules and functional groups Organic refers to molecules containing a carbon skeleton bonded to hydrogen atoms Inorganic refers to carbon dioxide and all molecules without carbon.

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why is carbon so important in biological molecules
Why Is Carbon So Important in Biological Molecules?
  • Organic/inorganic molecules and functional groups
    • Organic refers to molecules containing a carbon skeleton bonded to hydrogen atoms
    • Inorganic refers to carbon dioxide and all molecules without carbon
why is carbon so important in biological molecules1
Why Is Carbon So Important in Biological Molecules?
  • The carbon atom is key
    • Is versatile because it has four electrons in the outer shell
    • Is stable by forming up to four bonds
      • single, double, or triple covalent
    • Result organic molecules can assume complex shapes:
      • branched chains, rings, sheets, and helices
  • Functional groups in organic molecules
    • Are less stable than the carbon backbone and are more likely to participate in chemical reactions
    • Determine the characteristics and chemical reactivity of organic molecules
dehydration synthesis
Dehydration Synthesis
    • Small organic molecules (called monomers) are joined to form longer molecules (called polymers)
  • Monomers are joined together through dehydration synthesis, at the site where an H+and an OH-are removed, resulting in the loss of a water molecule (H2O)
  • The openings in the outer electron shells of the two subunits are filled when the two subunits share electrons, creating a covalent bond

dehydration

synthesis

hydrolysis
Hydrolysis
  • Polymers are broken apart through hydrolysis (“water cutting”)
    • Water is broken into H+and OH-and is used to break the bond between monomers
    • Digestive enzymes use to break down food

hydrolysis

biological molecules1
Biological Molecules

The important organic molecules found in living things:

Carbohydrates Lipids Proteins Nucleic Acids

Sugar Fat Enzymes Deoxyribonucleic

Starch Structural Proteins Ribonucleic Acid

Cellulose

All contain Carbon, Hydrogen, and generally Oxygen.

carbohydrates
Carbohydrates
  • Carbohydrate molecules are composed of C, H, and O in the ratio of 1:2:1
    • Monosaccharide - consists of just one sugar molecule
    • Disaccharide - Two linked monosaccharides
    • Polysaccharide - polymer of many monosaccharides
carbohydrates1
Carbohydrates
  • Hydrophilic due to the polar OH- functional group
    • Only mono- and disaccharides
  • Functions:
    • Energy source
    • Combine with other molecules through dehydration synthesis (plasma membrane, cell wall, exoskeletons)
carbohydrates2
Carbohydrates
  • There are several monosaccharides with slightly different structures
    • The basic monosaccharide structure is:
      • A backbone of 3–7 carbon atoms
      • Most of the carbon atoms have both a hydrogen (-H) and an hydroxyl group (-OH) attached to them
      • Chemical formula (CH2O)n

water

hydrogen

bond

hydroxyl

group

monosaccharides
Monosaccharides
      • When dissolved in the cytoplasmic fluid of a cell, the carbon backbone usually forms a ring
  • Glucose (C6H12O6) is the most common monosaccharide in living organisms
    • Fructose (“fruit sugar” found in fruits, corn syrup, and honey)
    • Galactose (“milk sugar” found in lactose)
    • Ribose and deoxyribose (found in RNA and DNA)

Note “missing”

oxygen atom

fructose

galactose

ribose

deoxyribose

disaccharides
Disaccharides
  • Functions:
      • They are used for short-term energy storage
      • When energy is required, they are broken apart by hydrolysis
  • Examples:
    • Sucrose (table sugar) = glucose + fructose
    • Lactose (milk sugar) = glucose + galactose
    • Maltose (malt sugar) = glucose + glucose

sucrose

glucose

fructose



dehydration

synthesis



polysaccharides
Polysaccharides
  • Storage polysaccharides include:
      • Starch, an energy-storage molecule in plants, formed in roots and seeds
      • Glycogen,an energy-storage molecule in animals, found in the liver and muscles

starch grains

(a) Potato cells

(b) A starch molecule

(c) Detail of a starch molecule

polysaccharides1
Polysaccharides
  • Polysaccharides as a structural material
    • Cellulose (a polymer of glucose)
      • It is found in the cell walls of plants
      • Most abundant organic molecule on Earth
      • It is indigestible for most animals due to the orientation of the bonds between glucose molecules
polysaccharides2
Polysaccharides
  • Chitin(a polymer of modified glucose units)
      • Nitrogen-containing functional group
      • The outer coverings (exoskeletons) of insects, crabs, and spiders
      • The cell walls of many fungi
slide16

Review

What are carbohydrates used for?

What are the major classes of carbohydrates?

What are the types and functions of polysaccharides?

lipids
Lipids
  • Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbon
    • All lipids contain large chains of non-polar hydrocarbons
    • hydrophobic
lipids1
Lipids
  • Lipids are diverse in structure and serve a variety of functions:
    • energy storage
    • waterproof coverings on plant and animal bodies
    • primary component of cellular membranes
    • hormones
  • Lipids are classified into three major groups
    • Oils, fats, and waxes
    • Phospholipids
    • Steroids
lipids2
Lipids
  • Oils, fats, and waxes
    • Carbon, hydrogen, oxygen
    • Made of one or more fatty acid subunits
    • Fats and oils
      • Are used primarily as energy-storage molecules, containing twice as many calories per gram as carbyhydrates and proteins
      • Are formed by dehydration synthesis
        • Three fatty acids + glycerol triglyceride
synthesis of a triglyceride
Synthesis of a Triglyceride

glycerol

fatty acids

Dehydration synthesis

triglyceride

Fig. 3-12

lipids3
Lipids
  • Oils, fats, and waxes
    • Fatsare solid at room temperature are saturated (the carbon chain has as many hydrogen atoms as possible, and mostly or all C-C bonds); for example, beef fat
    • Produced in animals
lipids4
Lipids
  • Oils, fats, and waxes
    • Oilsare liquid at room temperature are unsaturated (with fewer hydrogen atoms, and many C=C bonds); for example, corn oil
      • Produced by plants
      • Unsaturated trans fats have been linked to heart disease
lipids5
Lipids
  • Oils, fats, and waxes
    • Waxes are similar to fats
    • Most animals don’t have the enzymes to break them down.
    • Functions:
      • form waterproof coatings such as on:
        • Leaves and stems of landplants
        • Fur in mammals
        • Insect exoskeletons
      • used to build honeycomb structures
lipids6
Lipids
  • Phospholipids
    • These form plasma membranes around all cells
    • Phospholipids consist of two fatty acids + glycerol + a short polar functional group containing nitrogen
      • Hydrophilicpolar functional groups form the “head”
      • Hydrophobic non-polar fatty acids form the “tails”

variable

functional

group

phosphate

group

fatty acid tails

polar head

glycerol

backbone

(hydrophobic)

(hydrophilic)

lipids7
Lipids
  • Steroids
    • Composed of four carbon rings fused together with various functional groups protruding from them
    • Examples:
      • Cholesterol (animal cell membranes)
      • Male and female sex hormones
proteins
Proteins
  • Functions
      • Enzymes are proteins that promote chemical reactions
      • Structural proteins (e.g., elastin, keratin) provide support
  • Hormones
  • Antibodies
  • Toxins
proteins1
Proteins
  • Polymers of amino acids joined by peptide bonds
    • All amino acids have a similar structure
      • All contain amino and carboxyl groups
      • All have a variable “R” group
        • Some R groups are hydrophobic
        • Some are hydrophilic
        • Cysteine R groups can form disulfide bridges

variable

group

amino

group

carboxylic

acid group

hydrogen

proteins2
Proteins
  • The sequence of amino acids in a protein dictates its function
  • Amino acids are joined to form chains by dehydration synthesis
    • An amino group reacts with a carboxyl group, and water is lost

dehydration

synthesis

water

amino acid

amino acid

peptide



amino

group

amino

group

carboxylic acid

group

peptide

bond

proteins3
Proteins
  • Amino acids are joined to form chains by dehydration synthesis
    • The covalent bond resulting after the water is lost is a peptide bond, and the resulting chain of two amino acids is called a peptide
    • Long chains of amino acids are known as polypeptides
proteins4
Proteins
  • Proteins exhibit up to four levels of structure
    • Primary structure is the sequence of amino acids
    • Secondary structure is a helix, or a pleated sheet
      • Repeating structure with hydrogen bonds
    • Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds
    • Quaternary structure occurs where multiplepolypeptides are linked together
the four levels of protein structure
The Four Levels of Protein Structure

(b) Secondary structure:

Usually maintained by

hydrogen bonds, which

shape this helix

(a) Primary structure:

The sequence of amino acids

linked by peptide bonds

leu

val

heme group

lys

lys

gly

his

hydrogen

bond

ala

lys

val

(d) Quaternary structure:

Individual polypeptides are

linked to one another by

hydrogen bonds or disulfide

bridges

(c) Tertiary structure:

Folding of the helix results

from hydrogen bonds with

surrounding water molecules

and disulfide bridges between

cysteine amino acids

lys

helix

pro

Fig. 3-21

proteins5
Proteins
  • The functions of proteins are linked to their three-dimensional structures
    • Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure
    • Disruption of secondary and tertiary bonds leads to denatured proteins and loss of function
      • Extreme heat
      • Extreme changes in pH
      • UV radiation
nucleotides and nucleic acids
Nucleotides and Nucleic Acids
  • Nucleotides act as energy carriers and intracellular messengers
    • Nucleotides are the monomers of nucleic acid chains
    • Three parts:
      • Phosphate group
      • Five-carbon sugar
      • Nitrogen-containing base

phosphate

Deoxyribose Nucleotide

base

sugar

nucleotides and nucleic acids1
Nucleotides and Nucleic Acids
  • Nucleotides act as energy carriers
    • Adenosine triphosphate (ATP) is a ribose nucleotide with three phosphate functional groups
    • ADP and cAMP
    • NAD and FAD: electron carriers
nucleic acids
Nucleic Acids
  • DNA and RNA, the molecules of heredity
    • Polymers of nucleotides
      • DNA(deoxyribonucleic acid) is found in chromosomes and carries genetic information needed for protein construction
      • RNA (ribonucleic acid) makes copies of DNA and is used directly in the synthesis of proteins
nucleic acids1
Nucleic Acids
  • Each DNA molecule consists of two chains of millions of nucleotides that form a double helix linked by hydrogen bonds

hydrogen

bond