.. covalent bond or a glycosiolic link -bond is angular and forms a spiral called an alpha helix -if it branches, amylopectin is formed -cellulose is a 1-4 linkage of beta glucose -this creates a straight strand and not a helix -these bonds are rigid and require special enzymes (cellulase) to break them -the position of the beta glucose molecules alternates Lipids: -humans rarely eat pure lipids -cell membranes are primarily lipid and lipids can easily enter cells, carrying a foods flavor with them -a diet should have less than 30% fat, 55-65% carbs, and 10-15% protein -lipids are important as a source of energy, insulation (adipose tissue), cushions for the internal organs, as a lubricant, as an emulsifying agent (cholesterol in bile), as a structural component of cells (1/6 of brain is fat), cholesterol as a precursor molecule for vitamin D, cortisone, testosterone, progesterone, and estrogen -lipids are simplest biological molecules and are composed mostly of C, H and a few Os -they are energy rich because of the high C to H ratio -fat consists of a glycerol molecule connected by ester bonds to a 3 fatty acid molecule (this is a tryglyceride) -if the bonds between the carbons are single bonds, the fatty acid is saturated (fat formed is a saturate) -if they have multiple bonds, it is an unsaturated fat -a polysaturate is more than one fatty acid held together by single bonds -multiple bonds can be broken and extra hydrogens added through hydrogenation -short chained fats of unsaturated fatty acids are soft with a low b.p. -long chained fats of saturated fatty acids are harder with a high b.p.
-length of chains affects boiling point the most -to make an oil from a solid, you must hydrogenate it Steroids: -saturated fatty acids can be converted to the steroid cholesterol -triglycerides are monitored more closely in the blood than cholesterol -the amount of saturates converted to cholesterol is genetic -abnormal genes can cause excessive production (1 gene = severe heart disease, 2 = shortened life span) -liver produces cholesterol -steroids have a 5 ring shape -examples are androgens, estrogens, and cortisone Proteins: -there are 20 amino acids, 8 of which are essential and can be converted into any of the other 12 -protein rich foods are digested into amino acids and the body absorbs them to make their own proteins -liver cells convert them into absent aminos = transaminofication -proteins are synthesized on ribosomes in the cytoplasms of cells or on polysomes (ribosome chains0 -DNA codes proteins by copying its info onto a shorter strand known as mRNA (m = a message to synthesize a protein) -the message is received and a protein is synthesized -for synthesis all 20 are required -number, sequence and type of amino acids making up the protein is the primary structure – this is determined by DNA -secondary structure is the coiling or pleating of amino acid chains, caused by rigid peptide bonds which are bent by strong intermolecular attraction between hydrogens and oxygens of every fourth amino – this results in a regular, repeating twist or an alphahelix -chains lie parallel to one another and form hydrogen bonds between themselves – this is a beta sheet but is not very common -secondary structure is determined by intermolecular bonds -tertiary structure refers to the folds in the coiled chain -this is called by a thiol called cysteine – this can form a bridge when it meets another cysteine -when 2 cysteines meet, a disulfide link is formed -insulin has 6 cysteine amino acids and forms 3 bridges and a slightly globular protein -the more cysteine amino acids there are, the more folds or joints that result and the more globular the protein is -globular proteins are the”doers” that function because they have a particular shape due to the cysteine-cysteine sulfur bridges -some proteins may be a bunch of polypeptide chains close together -this is quaternary structure, which very few proteins have -all proteins have a primary and secondary structure, but few have a tertiary structure, and even fewer a quaternary -proteins can be 50-50,000 amino acids long -amino acids are joined by peptide bonds, a covalent bond between the C of one amino acid and the N of a neighbour -a polypeptide chain is a string of aminos not long enough to be a protein -amino acids are so named because of their two functional groups, the amine group and the carboxylic acid group Nucleic Acids: -all living cells contain DNA and RNA -these carry instructions for making proteins and specify the sequence in which amino acids should be linked together -DNA and RNA are polynucleotides, polymers of nucleotides -nucleotides consist of a phosphate group + a pentose + a nitrogenous base -they can be linked together by condensation to form a polynucleotide -if a nucleotide contains ribose, it becomes Ribo Nucleic Acid -these are always just a single strand, but may be looped into 3 dimensional shapes -if the nucleotide contains deoxyribose, Deoxyribo Nucleic Acid results -DNA molecules are far longer than RNA molecules, and can never contain Uracil -4 possible bases are adenine, guanine, cytosine, and thymine -DNA molecules contain two polynucleotide strands, held together by hydrogen bonds between the bases -hydrogen bonds can only be formed between specific base pairs: Adenine – Thymine Cytosine – Guanine -a sense strand is a sequence of bases that tells the order in which to string together the amino acids -a length of DNA coding the sequence for a polypeptide is called a gene -three bases, a codon, specify an amino acid -there are 64 possible arrangements of bases in a codon -polypeptides are made when 2 strands of DNA split up and an RNA molecule builds up against the sense strand -base sequence of RNA must match that of the DNA molecule -a complete RNA molecule then peels off and travels to the location where polypeptides are made -sequence of bases on a DNA molecule is the same for a human or a bacteria Other Nucleotides: -a slightly different version of one of the nucleotides that forms RNA is ATP -ATP contains ribose, adenine and 3 phosphate groups instead of 1 -phosphate groups may be lost one at a time to make ADP (di) or AMP (mono) -all living cells make ATP as an energy currency, it is produced constantly -ATP molecules usually last less than a minute before being broken down -~40 kg is produced in a day -if a cell needs energy, it hydrolyses ATP and releases energy in small packets NAD: -contains ribose sugar, adenine and 2 nucleotides -one nucleotide does not contain any of the 5 bases, but instead a nicotinamide ring -they can accept hydrogens and become NADH -hydrogens are accepted or passed on during respiration or photosynthesis.
