1. The Structure and Function of Macromolecules
Chapter 5
The Structure and Function of Macromolecules
Part B

2. Steroids Steroids Are lipids characterized by:
A carbon skeleton consisting of four fused rings

3. One steroid, cholesterol
Is found in cell membranes
Is a precursor for some hormones HO
CH3
H3C
Figure 5.15

4. Proteins have many structures, resulting in a wide range of functions
Have many roles inside the cell

5. An overview of protein functions
Table 5.1

6. Enzymes:
An enzyme is a type of protein that acts as a catalyst, speeding up chemical reactions
Substrate
(sucrose)
Enzyme
(sucrase)
Glucose OH
H O
H2O
Fructose
3 Substrate is converted
to products.
1 Active site is available for
a molecule of substrate, the
reactant on which the enzyme acts.
Substrate binds to
enzyme. 2
4 Products are released.
Figure 5.16

7. Polypeptides Polypeptides A protein Are polymers of amino acids
Consists of one or more polypeptides

8. Amino Acid Monomers Amino acids
Are the monomers (building blocks) of proteins
Are organic molecules possessing both carboxyl and amino groups
Differ in their properties due to differing side chains, called R groups

9. 20 different amino acids make up proteinsH
H3N+ C
CH3 CH
CH2 NH
H2C
H2N
Nonpolar
Glycine (Gly)
Alanine (Ala)
Valine (Val)
Leucine (Leu)
Isoleucine (Ile)
Methionine (Met)
Phenylalanine (Phe)
Tryptophan (Trp)
Proline (Pro)
H3C
Figure 5.17 S

10. Polar Electrically chargedOH
CH2 C H
H3N+ O
CH3 CH SH
NH2
Polar
Electrically
charged –O
NH3+
NH2+
NH+ NH
Serine (Ser)
Threonine (Thr)
Cysteine
(Cys)
Tyrosine
(Tyr)
Asparagine
(Asn)
Glutamine
(Gln)
Acidic
Basic
Aspartic acid
(Asp)
Glutamic acid
(Glu)
Lysine (Lys)
Arginine (Arg)
Histidine (His)

11. Amino Acid Polymers Amino acids Are linked by peptide bondsOH
DESMOSOMES OH
CH2 C N H O
Peptide bond SH
Side chains
H2O
Amino end (N-terminus)
Backbone
(a)
Figure 5.18
(b)
Carboxyl end (C-terminus)

12. Determining the Amino Acid Sequence of a Polypeptide
The amino acid sequences of polypeptides
Were first determined using chemical means
Can now be determined by automated machines

13. Protein Conformation and Function
A protein’s specific conformation
Determines how it functions

14. Four Levels of Protein Structure
Primary structure
Is the unique sequence of amino acids in a polypeptide
Figure 5.20 –
Amino acid subunits
+H3N Amino end o
Carboxyl end c
Gly
Pro
Thr
Glu
Seu
Lys
Cys
Leu
Met
Val
Asp
Ala
Arg
Ser
lle
Phe
His
Asn
Tyr
Trp
Lle

15. Secondary structure
Is the folding or coiling of the polypeptide into a repeating configuration
Includes the  helix and the  pleated sheet O C
 helix
 pleated sheet
Amino acid subunits N H R H
Figure 5.20

16. Is the overall three-dimensional shape of a polypeptide
Tertiary structure
Is the overall three-dimensional shape of a polypeptide
Results from interactions between amino acids and R groups
CH2 CH
O H O C HO
NH3+ -O S
CH3
H3C
Hydrophobic interactions and van der Waals interactions
Polypeptide backbone
Hyrdogen bond
Ionic bond
Disulfide bridge

17. Quaternary structure
Is the overall protein structure that results from the aggregation of two or more polypeptide subunits
Polypeptide chain
Collagen
 Chains
 Chains
Hemoglobin
Iron
Heme

18. The four levels of protein structure
+H3N
Amino end
Amino acid
subunits
helix

19. Sickle-Cell Disease: A Simple Change in Primary Structure
Results from a single amino acid substitution in the protein hemoglobin

20. Sickle-cell hemoglobin
Hemoglobin structure and sickle-cell disease
Primary structure
Secondary and tertiary structures
Quaternary structure
Function
Red blood cell shape
Hemoglobin A
Molecules do not associate with one another, each carries oxygen.
Normal cells are full of individual hemoglobin molecules, each carrying oxygen  
10 m
Hemoglobin S
Molecules interact with one another to crystallize into a fiber, capacity to carry oxygen is greatly reduced.
 subunit 1 2 3 4 5 6 7
Normal hemoglobin
Sickle-cell hemoglobin
. . .
Figure 5.21
Exposed hydrophobic region
Val
Thr
His
Leu
Pro
Glul
Glu
Fibers of abnormal hemoglobin deform cell into sickle shape.

21. What Determines Protein Conformation?
Depends on:
the physical and chemical conditions of the protein’s environment

22. Is when a protein unravels and loses its native conformation
Denaturation
Is when a protein unravels and loses its native conformation
Denaturing factors: pH and temperature
Denaturation
Renaturation
Denatured protein
Normal protein
Figure 5.22

23. Nucleic Acids Nucleic acids:
Are polymers of monomers (building blocks) called nucleotides.
Are the information storage molecules.
Provide the instructions for building proteins.
There are two types of nucleic acids:
DNA, deoxyribonucleic acid
RNA, ribonucleic acid

24. Different from DNA in that:
RNA, ribonucleic acid:
Different from DNA in that:
It is a single strand
Its sugar (ribose) has an extra OH group.
It has the base uracil (U) instead of thymine (T).

25. The genetic instructions in DNA
Nucleic Acids
The genetic instructions in DNA
Must be translated from “nucleic acid language” to “protein language.”
This process is called tanslation
Genes
Are the units of inheritance
They specify the amino acid sequence of polypeptides
Are segments of nucleic acids

26. Synthesis of mRNA in the nucleus
Nuclear DNA
Directs RNA synthesis
Directs protein synthesis through RNA 1 2 3
Synthesis of mRNA in the nucleus
Movement of
mRNA into cytoplasm
via nuclear pore
Synthesis
of protein
NUCLEUS
CYTOPLASM
DNA
mRNA
Ribosome
Amino acids
Polypeptide
Figure 5.25

27. The Structure of Nucleic Acids
Exist as polymers called polynucleotides
3’C
5’ end
5’C
3’ end OH
Figure 5.26 O
(a) Polynucleotide,
or nucleic acid

28. Each polynucleotide Consists of monomers called nucleotides
Nitrogenous
base
Nucleoside O O O P
CH2
5’C
3’C
Phosphate
group
Pentose
sugar
(b) Nucleotide
Figure 5.26

29. (c) Nucleoside components
Nucleotide Monomers
Nucleotide monomers
Are made up of nucleosides and phosphate groups CH
Uracil (in RNA) U
Ribose (in RNA)
Nitrogenous bases Pyrimidines C N O H
NH2 HN
CH3
Cytosine
Thymine (in DNA) T HC NH
Adenine A
Guanine G
Purines
HOCH2 OH
Pentose sugars
Deoxyribose (in DNA) 4’ 5” 3’ 2’ 1’
Figure 5.26
(c) Nucleoside components

30. Nucleotide Polymers Nucleotide polymers
Are made up of nucleotides linked by:
the–OH group on the 3´ carbon of one nucleotide, and
the phosphate on the 5´ carbon on the next

31. Each DNA nucleotide has one of the following bases:
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
The sequence of bases along a nucleotide polymer is:
unique for each gene

32. Cellular DNA molecules
The DNA Double Helix
Cellular DNA molecules
Have two polynucleotides (strands)
The two strands spiral around an imaginary axis forming a double helix
The double helix consists of two antiparallel nucleotide strands

33. The DNA double Helix Figure 5.27 3’ end Sugar-phosphate backbone
Base pair (joined by hydrogen bonding)
Old strands
Nucleotide about to be added to a new strand A
5’ end
New strands
Figure 5.27

34. The nitrogenous bases in DNA
Form hydrogen bonds in a complementary fashion:
A binds with T only (thru two H bonds)
C binds with G only (thru three H bonds)

35. DNA and Proteins as Tape Measures of Evolution
Molecular comparisons:
Help biologists sort out the evolutionary connections among species

36. Figure 3.30