1. Proteins have many structures, resulting in a wide range of functions
Proteins account for more than 50% of the dry mass of most cells
The monomers (building units) of proteins are amino acids.
Cells use 20 amino acids to make thousands of proteins

2. Amino Acid Monomers
Amino acids are organic molecules with carboxyl and amino groups
a carbon
Amino
group
Carboxyl
group

3. Amino acids are linked by peptide bonds formed by dehydration reactions
Side chains
Backbone
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
(b)

4. Polypeptides Polypeptides are polymers of amino acids
A protein consists of one or more polypeptides
Lysozyme: an antibacterial enzyme (protein) found in human tears.
It is made of one polypeptide.
Hemoglobin protein is made of four polypeptides

5. Fig. 5-22 Normal hemoglobin Sickle-cell hemoglobin Primary structure
Val
His
Leu
Thr
Pro
Glu
Glu
Val
His
Leu
Thr
Pro
Val
Glu 1 2 3 4 5 6 7 1 2 3 4 5 6 7
Exposed
hydrophobic
region
Secondary
and tertiary
structures
Secondary
and tertiary
structures
 subunit
 subunit    
Quaternary
structure
Normal
hemoglobin
(top view)
Quaternary
structure
Sickle-cell
hemoglobin    
Function
Molecules do
not associate
with one
another; each
carries oxygen.
Function
Molecules
interact with
one another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.
10 µm
10 µm
Red blood
cell shape
Normal red blood
cells are full of
individual
hemoglobin
moledules, each
carrying oxygen.
Red blood
cell shape
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.

7. Four Levels of Protein Structure
Primary structure
Secondary structure
Tertiary structure
Quaternary structure

8. Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word

9. Figure 3.7 The Four Levels of Protein Structure (Part 1)
Figure 3.7 The Four Levels of Protein Structure The primary structure (A) of a protein determines what its secondary (B and C), tertiary (D), and quaternary (E) structures will be.

10. Secondary Structure
The coils and folds of secondary structure result from hydrogen bonds between atoms of the polypeptide backbone (NOT the amino acid side chain or R-groups).
Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet.

11. Figure 3.7 The Four Levels of Protein Structure (Part 2)
Figure 3.7 The Four Levels of Protein Structure The primary structure (A) of a protein determines what its secondary (B and C), tertiary (D), and quaternary (E) structures will be.

12. Abdominal glands of the spider secrete silk fibers
Fig. 5-21d
Abdominal glands of the
spider secrete silk fibers
made of a structural protein
containing -pleated sheets.
The radiating strands, made
of dry silk fibers, maintain
the shape of the web.
The spiral strands (capture
strands) are elastic, stretching
in response to wind, rain,
and the touch of insects.

13. Tertiary Structure
Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents
These interactions between R groups include:
hydrogen bonds,
ionic bonds,
hydrophobic interactions,
van der Waals interactions
Strong covalent bonds called disulfide bridges may reinforce the protein’s conformation.

14. Figure 3.7 The Four Levels of Protein Structure (Part 3)
Figure 3.7 The Four Levels of Protein Structure The primary structure (A) of a protein determines what its secondary (B and C), tertiary (D), and quaternary (E) structures will be.

15. Quaternary structure
Quaternary structure results when two or more polypeptide chains form one macromolecule
Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains

16. Concept 5.5: Nucleic acids store and transmit hereditary information
The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
Genes are made of DNA, a nucleic acid

17. The Roles of Nucleic Acids
There are two types of nucleic acids:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
DNA replicates in order for the cells to divide
DNA directs the synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
Protein synthesis occurs in ribosomes

18. Concept 3.1 Nucleic Acids Are Informational Macromolecules
DNA’s information is encoded in the sequence of bases. DNA has two functions:
Replication
Information is copied to RNA and used to specify amino acid sequences in proteins.

19. LE 5-25
DNA directs the synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
DNA
Synthesis of
mRNA in the nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
Synthesis
of protein
Amino
acids
Polypeptide

20. The Structure of Nucleic Acids
Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
Each nucleotide consists of:
a nitrogenous base
a pentose sugar
and a phosphate group

21. Nitrogenous base Phosphate group Pentose sugar
LE 5-26a
5¢ end
Nucleoside
Nitrogenous
base
Phosphate
group
Pentose
sugar
Nucleotide
3¢ end
Polynucleotide, or
nucleic acid

22. Nitrogenous bases There are two families of nitrogenous bases:
Pyrimidines have a single six-membered ring
Purines have a six-membered ring fused to a five-membered ring.
Pyrimidines
Nitrogenous bases
Cytosine C
Thymine (in DNA) T
Uracil (in RNA) U
Purines
Adenine A
Guanine G

23. Pentose sugar In DNA, the sugar is deoxyribose
In RNA, the sugar is ribose.
Pentose sugars
Deoxyribose (in DNA)
Ribose (in RNA)

24. The DNA Double Helix
A DNA molecule has two polynucleotides spiraling around an imaginary axis, forming a double helix
The nitrogenous bases in DNA form hydrogen bonds in a complementary fashion: A always pairs with T, and G always pairs with C

25. Figure 3.4 DNA
Figure 3.4 DNA (A) DNA usually consists of two strands running in opposite directions that are held together by base pairing between purines and pyrimidines opposite one another on the two strands. (B) The two antiparallel strands in a DNA molecule are twisted into a double helix.

26. Concept 3.1 Nucleic Acids Are Informational Macromolecules
The two strands are antiparallel (running in opposite directions), and the double helix is right-handed.

27. RNA RNA is made of one polynucleotide (one strand of nucleotides)
The nucleotide of RNA is made of:
A nitrogenous bases, Adenine (A), Uracil (U), Guanine (G), or Cytosine (C).
A ribose sugar.
A phosphate group.

28. Concept 3.1 Nucleic Acids Are Informational Macromolecules
DNA replication and transcription depend on base pairing:
5′-TCAGCA-3′
3′-AGTCGT-5′
transcribes to RNA with the
sequence 5′-UCAGCA-3′.

29. Differences between DNA and RNA
Composed of two strands of polynucleotides twisted together helically to form a double helix
Composed of one strand of polynucleotides.
Contains the 5-carbon sugar Deoxyribose
Contains the 5-carbon sugar Ribose

30. Differences between DNA and RNA
Contains the nitrogenous bases Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)
Adenine pairs with Thymine and Guanine pairs with Cytosine.
Contains the nitrogenous bases Adenine (A), Uracil (U), Guanine (G), and Cytosine (C)
Larger molecule.
Shorter than DNA