The document summarizes key concepts about protein structure and types of proteins. It contains the following key points: 1. Protein structure is organized into four levels: primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence, secondary structure involves coiling and folding into shapes like alpha helices and beta sheets. Tertiary structure involves further compact folding, and quaternary structure involves multiple polypeptide chains combining. 2. Proteins can be simple, only containing amino acids, or conjugated, containing non-polypeptide groups. Simple proteins include fibrous (insoluble) and globular (soluble) types. Conjugated proteins include nucleopro

1. Left top: Atomic force microscopy (AFM)
topographs of native membrane proteins
(a) Ion-driven rotors from spinach chloroplast and
(b) Illyobacter tartaricus FoF1-ATP synthase (c)
High-light-adapted native photosynthetic
membrane from Rhodospirillum photometricum.
Left bottom: Spatial arrangements of GFP
polygons and displayed functional proteins were
visualized by TEM.
Right top: The western blot (the protein
immunoblot) is used to detect specific
proteins

2. 1.5 Protein

3. Learning objectives
• Function and importance of protein
• Chemical composition of protein
• Amino acid as the monomer of protein

4. Importance of protein 蛋白质
• Second most abundant class of molecules in a cell
• Forming structure of cells (Structural proteins)
• Keratin 角蛋白 – hair, horn, nails, scales
• Actin – microfilament (a cytoskeleton)
• Myosin - producing muscle contraction in muscle cells
• Collagen - tendons and hides of connective tissues
• Performing cellular functions
• Messenger proteins (e.g. Hormones – oxytoxin, insulin)
• Enzymes – amylase, protease, DNA ligase, polymerase
• Transport proteins – haemoglobin, ion channel, cytochromes
A pair of horns on a male impala.
高角羚
Amylase in the saliva breaks down
starch into glucose.

5. Quiz
• Which is not the functions of proteins in human bodies?
a. Molecules to replace cellular components
b. Main component of enzyme
c. Materials to repair damage cells
d. Energy source

6. Quiz
• These proteins are responsible for building arrangements in
organisms.
a. hormones
b. enzymes
c. structural proteins

7. 鷹嘴豆泥

8. Chemical composition of protein
• Composed of carbon, hydrogen,
nitrogen and oxygen
• May contain phosphorus, sulfur
(sulphur), iron, copper, manganese,
iodine, zinc etc.
Amyloid beta-protein

9. Quiz
• Proteins are ________ polymers.
a. inorganic
b. organic

10. Monomers 单体 of protein
• Proteins are polymers 聚合物, relatively
large molecules made from many smaller
molecules.
• Amino acid is the monomer of protein.
• Amino acid has
• a carboxyl group (-COOH) 羧suō基
• an amino group (-NH2) 氨基
• A side chain (denoted as R) 支链 R基
• The side chain is variable and determine the
properties (charge, acidic/basic, size).
• There are about 20 different amino acids.

12. Quiz
• Amino acids contain carbon, hydrogen, oxygen, and what other main
element?
a. nitrogen
b. phosphorous
c. iron
d. magnesium

13. Quiz
• Proteins are long chains of ____________
a. amino acids
b. polymers
c. enzymes

14. Amphoteric 两性 amino acids
• An amphoteric compound is a molecule or ion that can react both as
an acid as well as a base.
• Acid donates proton (H+) 质子 and bases accept proton.
• Amino acids contain both acidic carboxyl group -(COOH) and basic
amino group (-NH) in the same molecules.
两性离子 负离子正离子

15. Quiz
• Amino acids in solution are______.
a. Neutral charge ion, not related to the pH of solution
b. Positive charge ion, not related to the pH of solution
c. Negative charge ion, not related to the pH of solution
d. Neutral, positive or negative charge ions, depend on the pH of
solution

16. Essential & non-essential amino acids
• Human can synthesize some amino acids de novo 从头合成.
• Those amino acids are referred as non-essential amino acids.
• Amino acids that cannot be synthesized in human bodies are called
essential amino acids.
• Essential amino acids must be supplied from the diet.

17. Protein in the diet
• First class proteins provides all the essential amino acids.
• Animal proteins (cheese, lean meat, fish, yolk, milk, shrimp )
• Soybean/soya bean, quinoa
• Second class proteins lack some of the essentials amino acids.
• Most plant protein
High-protein foods.

18. Quiz
• What is the main difference between essential and nonessential
amino acids?
a. The body can function properly without essential amino acids.
b. The body can make non-essential amino acids, but it cannot make
essential amino acids.
c. The body can make essential amino acids, but it cannot make non-
essential amino acids because they are only needed during times of
rapid development
d. The body can function properly without non-essential amino acids.

19. Condensation of amino acids
• Amino acids joined together by peptide bonds to form peptides.
• A peptide bond is made between the carbonyl carbon and the nitrogen.
• A molecule of water is lost for every peptide bond formed.
• Dipeptide 二肽 = two amino acids
• Polypeptide 多肽 = three or more amino acids

20. Peptide bond
• Step 1: The single-bonded
oxygen atom is removed from
the carboxyl group on the left-
most amino acid. Two
hydrogen atoms are removed
from the amino group on the
right-most amino acid. The
oxygen atom and the two
hydrogen atoms combine to
form a water molecule.
• Step 2: A peptide bond is
made between the carbonyl
carbon and the nitrogen.

21. Writing convention of peptide sequences
• By convention, peptide sequences are written N-terminus to C-
terminus.
N-terminus C-terminus
N 端 C 端
A tetrapeptide (example: Val-Gly-Ser-Ala) with green highlighted N-terminal amino acid (example: valine) and
blue marked C-terminal amino acid (example: alanine).

22. Quiz
• An amino acid molecule has the following structure:
H
H2N C COOH
R
Which two of the groups combine to form a peptide link?
A. 1 and 2
B. 2 and 3
C. 1 and 3
D. 2 and 4
①
②
③
④

23. Conclusion
• Protein is composed of carbon, hydrogen, nitrogen and oxygen and it
may contain phosphorus, sulfur (sulphur), iron, copper, manganese,
iodine, zinc etc.
• Protein is important for forming structure of cells and performing
cellular functions.
• Amino acid is the monomer of protein. Amino acid has a carboxyl
group (-COOH), an amino group (-NH2) and a side chain (R).
• Amino acids are amphoteric and soluble in water.
• Essential amino acid cannot be synthesized in our body and has to be
obtained from diet.
• First class proteins provide all the essential amino acids while second
class proteins lack some of the essentials amino acids.
• Polypeptides are polymers of amino acids.
• Peptide bonds connect amino acids.

24. Top: Allosteric 变构 motion of hemoglobin, with hemes in red
and with an oxygen molecule in turquoise.
Left: Cross section through ebola virus shows proteins in blue,
green and magenta, the RNA genome in yellow, and the
membrane in light purple. Atomic structures are shown on the
right, with portions that have not been determined shown with
schematic circles.

25. Quiz
• Proteins are made from long, folded chain molecules. What are these
chains called?
a. polysaccharides
b. polypeptides
c. polynucleotides
d. fatty acids

26. Quiz
• A peptide bond is formed between
a. An aldehyde group and an amino group
b. An aldehyde group and a carboxyl group
c. A carboxyl group and an amino group
d. A carboxyl group and an ester group

27. 1.5 Protein

28. Objectives
• Three dimensional arrangement of peptides
• Simple protein and conjugated protein

29. Arrangement of peptides
• Peptides generally forms peptide chains.
• Peptide chains forms three dimensional
structure.
• A protein may contain one or more peptide
chains.

30. Primary structure 一级结构
• The order of the amino acid residues in a peptide or protein is
referred to as its primary structure.
• Covalent bonds (peptide bonds) joins amino acids together.

31. Secondary structure 二级结构
• Peptide chains are
coiled and folded into
specific shape
• e.g. ∝-helix α螺旋
or 𝛽-sheet β折叠.
• Hydrogen bonding
between an N-H in one
peptide group and a
C=O in another peptide
group.

32. Tertiary structure 三级结构
• Alpha helices and/or beta
sheets, along with the
unorganized sections of a
peptide chain, “fold” into
a more compact shape.
• The structure is
maintained by ionic,
disulphide and hydrogen
bonding.

33. Quaternary structure
• Different polypeptide chains
combine with associated non-
protein groups to form a large
complex protein molecule.
• The folding pattern can be
called a conformation 构象 of
protein.
• Each of the polypeptide
chains is called a subunit.
Hemoglobin is composed of four protein chains, two alpha
chains and two beta chains, each with a ring-like heme group
(red) containing an iron atom.

34. Levels of
protein
organization

35. Quiz
• The primary structure of protein is maintained by
a. Peptide bond
b. Hydrogen bond
c. Ionic bond
d. Disulphide bond

36. Protein classes based on composition
• Simple protein only contain amino acids.
• Conjugated protein contain non-polypeptide groups (metal ions,
lipids, saccharides).
Serum albumin 血清白蛋白 , with bound fatty acids in
white and red, delivers fatty acid molecules through the
bloodstream.
Hemoglobin 血红蛋白, with hemes in red.

37. Simple protein
• Fibrous protein 硬蛋白/纤维状蛋
白[质]
• Insoluble in water
• Collagen fiber 膠原蛋白, myosin 肌
凝蛋白, fibrin 纖維蛋白, keratin 角
质素
• Globular protein 球蛋白
• Soluble in water
• Enzyme (amylase 淀粉酶, rennin 粗
制凝乳酶), hormones (oxytocin 催
产素, vasopressin 抗利尿激素),

38. Conjugated protein
• Nucleoprotein
• Nucleic acid + protein
• Ribosomes 核糖体, nucleosomes 核小体
• Lipoprotein
• Lipid + protein
• Low-density lipoprotein (LDL) 低密度脂蛋白,
High-density lipoprotein (HDL)高密度脂蛋白
• Glycoprotein
• Polysaccharide + protein
• miraculin 神秘果蛋白, thyroid-stimulating
hormone 促甲状腺激素
Miraculin, extracted from Synsepalum dulcificum of West Africa, binds to sweet
receptors on the tongue causing acidic foods which are ordinarily sour (such
as citrus) are perceived as sweet.

39. Conclusion
• Protein configuration is fundamentally based on its amino acid sequence or
its primary structure.
• Peptide chains are coiled and folded into specific shape in their secondary
structure.
• Alpha helices and/or beta sheets, along with the unorganized sections of a
peptide chain, “fold” into a more compact shape.
• Different polypeptide chains combine with associated non-protein groups
to form a large complex protein molecule in quaternary structure.
• Simple protein only consists of amino acids, such as fibrous protein
(insoluble in water) and globular protein (soluble in water).
• Conjugated protein contain non-polypeptide groups (metal ions, lipids,
saccharides) such as nucleoprotein, lipoprotein and glycoprotein.

40. Quiz
• The secondary order of protein structure is
a. The sequence of amino acids in the polypeptide chain
b. The coiling of the polypeptide chain
c. The folding of the coiled polypeptide chain
d. The linking together of two or more polypeptide chains

41. Short-answer questions
(1) Write one structure of amino acids.
(2) Why do amino acids have amphoteric characteristic?
(3) Peptide that formed by 20 amino acids molecules has how many
peptide bond?
(2) It possesses an acidic carboxyl group and a
basic amino group and hence can react both as an
acid and as a base.
(3) 19 peptide bonds

42. Short-answer questions
• What is simple protein and conjugated protein?
• Simple protein only contains amino acids, e.g. myoglobin, enzyme,
and hormones, while conjugated protein contains amino acids and
other non-amino acids groups, for examples, nucleoprotein of
chromosome is synthesized from nucleic acid and protein, and
lipoprotein of plasma membrane is synthesized from lipid and
protein.

43. Quiz
• Which of these is not a globular protein?
a. The skin protein collagen
b. The hormone insulin
c. The enzyme amylase
d. The oxygen carrier haemoglobin