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Chapter 5-The structure and function of Large Biological Molecules
C-5 The Structure and Function of Large Biological Molecules
(Carbohydrates, Lipids and Proteins and Nucleic Acids)
Carbohydrates
• Carbohydrates- organic compounds composed of carbon, hydrogen and oxygen
• Generally contain hydrogen and oxygen in a 2:1 ratio. Example Glucose.
Functions of Carbohydrates
• Energy storage molecules. Starch in plants and glycogen in animals.
• Immediate energy source- Glucose
• Structural components- cellulose in plant cell walls and chitin in the exoskeleton of insects, crustaceans.
• Monosaccharides- the fundamental building blocks of carbohydrates.They are simple sugars such as Glucose and Fructose.
• Disaccharides-when two monosaccharides are joined together we have disaccharides.
Examples:
• Glucose + Glucose = Maltose
• Glucose + Fructose = Sucrose
• Polysaccharides are many monosaccharides (more than 2) joined together in long chains.Starch, glycogen, cellulose and chitin. Fig 5.7
• To form disaccharides and polysaccharides requires a condensation (dehydration) reaction. (Water must be removed)
• Fig 5.5 text
• To break down a polysaccharide requires the addition of a water molecule.
• Example: Starch>> Sucrose>> Glucose
• This is called a hydrolysis reaction
Lipids
• Fats
• Phospholipids
• Steroids
• Fats- composed of 1 glycerol molecule and 3 fatty acid molecules (Triglycerides)
• To make a fat requires a dehydration reaction.
• Fig 5.10
• Fats can store twice as much energy as carbohydrates and proteins and are hydrophobic. Also used for cushioning and insulation
Fats may be Saturated or Unsaturated
• Saturated Fats- every carbon in the chain except the last one holds 2 hydrogen atoms. This means that it is full or saturated with hydrogen and can hold no more.
• They are usually solids because of this and are animal products- Butter
• Unsaturated Fats- contain carbon atoms joined by double bonds and therefore do not contain the maximum number of hydrogens
• They are usually plant products and are liquids. Corn oil.
Phospholipids
• Phospholipids- are composed of 2 fatty acids and 1 glycerol molecule. They are part hydrophilic and part hydrophobic.
• They are the major components of cell membranes.
Steroids
(Cholesterol and Sex Hormones)
• Cholesterol- is used in the construction of cell membranes and the proper functioning of nerves. It is also used for the production of certain hormones and to make bile acids which help you to digest your food.It is made in the liver and also taken in with diet.
• Sex hormones-estrogen and testosterone.
• Cholesterol+Fats - excess can lead to atherosclerosis.
• Heart attack and stroke.
Proteins
• Proteins have a variety of functions. They are assembled from 20 amino acids under the direction of your genes.
• Each amino acid has a carboxyl group and an amino group. (Fig 5.16)
Functions of Proteins
• Structural proteins-hair, horns, feathers, tendons , ligaments.
• Transport proteins- Hemoglobin
• Hormonal proteins- Insulin
• Receptor proteins- Nerve cell to nerve cell
• Contractile proteins- actin and myosin in muscles
• Defensive proteins-antibodies
• Enzymatic proteins- digestion of food and other chemical reactions.
Levels of Protein Structure
• Primary
• Secondary
• Tertiary
• Quaternary
• Primary Structure- this is a proteins unique sequence of amino acids which in turn determines its biological function
• Fig 5.18
• Any change in the primary structure will change the function of the protein
• Example: the normal sequence for the protein hemoglobin is:
• Val-His-Leu-Thr-Pro-Glu-Glu----146
• For defective (Sickle Cell) hemoglobin it is:
• Val-His-Leu-Thr-Pro-Val-Glu----146
• Secondary structure- is when the protein begins to fold and coil and is due to hydrogen bonds.
• Fig 5.20
• Examples are hair, muscle and silk
• Tertiary structure- results from a secondary structure folding back upon itself and results from hydrogen bonds, ionic bonds, disulfide bridges and other molecular interactions.
• Examples; enzymes and antibodies.
• Quaternary structure- results from 2 or more polypeptide chains interact to form a functional protein
• Fig. 5.23
• Collagen and Hemoglobin
• In addition to the 4 levels of structure a proteins function and structure also depends on the physical and chemical environment that surrounds it.
• pH, salt concentration, temperature.
• If these change then the protein will denature (fall apart) and no longer function. Fig 5.25
Nucleic Acids
(Information Molecules)
• Nucleic acids- store and transmit hereditary information. These molecules are what your genes are made of. DNA is found in your 46 chromosomes which are located in the nucleus of the cell.
• There are 2 types: DNA and RNA
• DNA stands for Deoxyribonucleic acid
• RNA stands for Ribonucleic acid of which there are 2 types: mRNA and tRNA
• (Fig 5.26)
Structure of Nucleotides
• Each nucleotide is composed of 3 parts:
• Nitrogenous base- of which there are four: Adenine, Thymine, Cytosine, Guanine
• Pentose sugar (ribose or deoxyribose)
• Phosphate group
• RNA does not contain the base thymine but has uracil instead.
• DNA- 2 strands. RNA- 1 strand.
Differences in DNA and RNA
1. DNA- The sugar is Deoxyribose.DNA-The bases are:Thymine,adenine,guanine and cytosine. DNA is double stranded. DNA has one less oxygen atom than RNA.
2.RNA the sugar is Ribose, the bases are uracil, adenine, guanine and cytosine, it is single stranded and has one more oxygen atom than DNA.
The closer the DNA (genes) of any two species is then the closer they are related to each other biochemically because their proteins will be similar
• Example: Humans and Gorillas
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