1. Ch. 5 Macromolecules: Lipids, Proteins, and Nucleic Acids
AP Biology
Ch. 5 Macromolecules:
Lipids, Proteins, and Nucleic Acids

2. Lipids Fats store large amounts of energy.
Triacylglycerols (triglycerides) are constructed by the joining of a glycerol molecule to three fatty acids.
Formed by dehydration synthesis reactions.

4. Saturated vs. Unsaturated Fats
Saturated fatty acids have the maximum number of hydrogen atoms. These tend to be solid at room temp., such as butter and meat fat.
Unsaturated fatty acids have one or more double bonds in their hydrocarbon chains. These tend to be liquid at room temp., such as olive oil and canola oil.
Unsaturated fats are generally considered to be healthier when used in moderation.

6. Phospholipids
Where fats have a third fatty acid linked to glycerol, phospholipids have a negatively charged phosphate group.
This makes the “head” of the phospholipid hydrophilic; the hydrocarbon “tails” are hydrophobic.
Phospholipids are the major components of cell membranes. In a cell membrane, the hydrophobic tails are orientated inward, while the hydrophilic head face outward.

9. Steroids
Steroids include cholesterol and certain hormones, such as testosterone and estrogen.
Steroids have a basic structure of four fused rings of carbon atoms.

10. Proteins Proteins are macromolecules of polypeptide chains.
Polypeptide are polymers of amino acids arranged in a specific linear sequence linked by peptide bonds.
Proteins are one or more polypeptide chains folded and coiled into specific conformations (3-D shapes).

11. Proteins, cont. Proteins make up 50% of cellular dry weight.
Each type has a unique 3-D shape.
Vary in structure and function, but all are made from the same 20 amino acids.

12. Proteins: Cellular function
Structural support
Storage of amino acids
Transport, such as hemoglobin
Signaling, chemical messengers
Cellular response to chemical stimuli (receptor proteins)
Movement (contractile proteins)
Defense (antibodies)
Catalysis of biochemical reactions (enzymes)

14. Amino Acids: Building blocks of proteins
Amino acids consist of an asymmetric carbon bonded to a hydrogen atom, carboxyl group, amino group, and a side chain (R-group) specific for each amino acid.
Physical and chemical properties of the side chain determine the uniqueness of each amino acid.

15. Groups of Amino Acids
Amino acids are put into groups based on the side chains the molecule contains, and its properties.
Nonpolar, hydrophobic side groups make amino acids less soluble in water.
Polar, hydrophilic side groups make amino acids soluble in water. These can be uncharged polar side groups, or charged (acidic or basic) groups.

16. NONPOLAR AMINO ACIDS

17. POLAR AMINO ACIDS

18. Peptide bonds
Peptide bonds are covalent bonds formed by a condensation reaction that links the carboxyl group of one amino acid to the amino group of another.
Has polarity with an amino group one end (N-terminus) and a carboxyl group on the other (C-terminus).
Has a backbone of repeating N-C-C-N-C-C
Polypeptide chains range in length from a few monomers to more than a thousand, and a unique linear sequence of amino acids.

19. Protein conformation: 3-D structure
Each protein molecule has a unique native conformation (shape of the protein under normal biological conditions) that reflect its function.
Enables a protein to recognize and bind specifically to another molecule (enzyme/substrate, hormone/receptor, antibody/antigen)

20. 3-D structure, cont.
A protein’s shape is produced when a newly formed polypeptide chain coils and folds spontaneously, mostly in response to hydrophobic interactions.
Is stabilized by chemical bonds and weak forces between neighboring regions of the folded protein.

21. Overview of Protein Structure

22. Four levels of protein structure
Primary- amino acid sequence
Secondary- regular repeated coiling and folding of a protein’s amino acid chain
Tertiary- 3-dimensional shape of a protein due to bonding between side chains
Quaternary- results from interactions between several polypeptide chain (protein has subunits, like hemoglobin and collagen)

23. Primary
Structure

25. Secondary Structure Coiling and folding of the polypeptide backbone
Stabilized by hydrogen bonds between peptide linkages in the amino acid chain
Two major types:
Alpha helix- helical coil stabilized by hydrogen bonds between every 4th peptide bond. Found in fibrous proteins such as collagen.
Beta pleated sheet- antiparallel chains fold into accordian-like pleats, held by hydrogen bonds. Form the dense core of globular proteins (lysozyme) and some fibrous proteins (silk)

26. Secondary
Structure:
Alpha helix or
Beta-pleated sheet

27. Spider silk: a structural protein

28. Tertiary structure
3-D shape of a protein due to bonding between side chains, and interactions with the aqueous environment.
Protein shape is stabilized by:
Weak interactions such as hydrogen bonding between side chains, ionic bonds between charged side chains, and hydrophobic interactions between nonpolar side chains
Covalent linkages such as disulfide bridges between two cysteine monomers brought together by protein folding

30. Quaternary structure
Occurs in proteins made up of two or more polypeptides, resulting from the interactions between them.
Collagen is a fibrous protein with three helical polypeptides supercoiled into a triple helix; makes it very strong connective tissue in animals
Hemoglobin is a globular protein with four subunits that fit together.

32. Protein conformation
Protein’s 3-D shape is a consequence of the interactions responsible for secondary and tertiary structure.
Protein conformation is influenced by the physical and chemical environment
If a protein’s environment is changed, it may become denatured and lose its shape.

34. Denaturation
Process that changes a protein’s structure, therefore affecting its biological function. Can be caused by:
Heat- disrupts weak interactions
Chemical agents that disrupt H-bonds, ionic bonds, and disulfide bridges (pH for example)
Transfer to an organic solvent causes hydrophobic chains to move toward the outside, while the hydrophilic side chains turn toward the interior.

35. Protein folding
3-D shape is hard to predict from amino acid sequence alone.
Protein’s native conformation may alternate between several shapes with folding occurring in stages.
Biochemists can now track a protein as it goes through the folding process.
Chaperone proteins temporarily brace a folding protein.

36. Nucleic Acids: Informational Polymers
Nucleic acids store and transmit hereditary information.
DNA stores information for the synthesis of specific proteins.
RNA, specifically mRNA, carries this genetic information to the protein synthesizing machinery (ribosomes).

37. Nucleic acids, cont. Nucleic acids are polymers of nucleotides.
Each nucleotide monomer consists of a pentose (5-C sugar) covalently bonded to a phosphate group and to one of four nitrogenous bases (A,G,C, T or U).
In making a chain, nucleotides join to form a sugar-phosphate backbone from which the nitrogenous bases project.
The sequence of bases along a gene specifies the amino acid sequence of a particular protein.

39. DNA: Deoxyribonucleic acid
DNA is a helical, double-stranded macromolecule with bases projecting into the interior of the molecule.
DNA has the pentose, deoxyribose. Adenine hydrogen bonds to thymine, and cytosine to guanine (Chargaff’s rule).
One DNA strand serves a template for a new strand.

41. X-ray evidence of DNA structure
In the early 1950’s, Rosalind Franklin studied DNA using X-ray diffraction.
The patterns in her pictures showed the DNA formed a coil shape (helix).
Her studies indicated that there were two strands, and that the nucleotides were toward the center of the molecule.

42. Franklin’s X-ray diffraction of DNA

43. Watson and Crick
James Watson and Frances Crick were working on the structure of DNA in the 1950’s also.
Using information from Chargaff, Franklin, and other scientists, they put together a 3-D model of DNA.
Their model was a double helix, with H-bonded nitrogenous bases holding the strands together.
The won the Nobel Prize for their work.

45. Ribonucleic Acid (RNA)
RNA is a single-stranded macromolecule with the 5-C sugar ribose.
In RNA, adenine binds to uracil instead of thymine, and guanine binds to cytosine.
RNA uses the information from DNA to assemble protein.

46. Types of RNA
Messenger RNA (mRNA)-carries messages from DNA for assembling amino acids into proteins (made during transcription).
Ribosomal RNA (rRNA)-Proteins and rRNA make up ribosomes, the site of protein synthesis.
Transfer RNA (tRNA)- transfers each amino acid to the ribosome as specified by codes in the mRNA.