生物化学与分子生物学第一章蛋白质ppt(八年制英文课件)

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(1) Non-polar and aliphatic AAs
• • •
R groups are non-polar, hydrophobic aliphatic groups. R groups are uncharged. AAs are insoluble in H2O.
(2) Neutral polar AAs

The average nitrogen content in proteins is about 16%, and proteins are the
major source of N in biological systems.

The protein quantity can be estimated:
protein in 100g sample = N per gram x 6.25 x 100
1/16%
Melamine (三聚氰胺)

It contains 67% nitrogen by mass
Melamine is a kind of white crystalline powders, without special smell.
Melamine has good water solubility. The price is only 1/5 of the price of protein raw materials

§1.1 Amino Acids
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The basic building blocks of proteins
•
•
AAs are highly hydrophilic.
Hydroxyl Amino Acids
Sulfur Amino Acids
Branched-chain Amino Acids
Special amino acids - Gly

optically inactive
+ -
H3N C H
(3) Aromatic AAs
• • •
R groups are aromatic groups. R group of Phe is non-polar and uncharged. R groups of Trp and Tyr are polar, but uncharged at neutral pH (=7.0).
The Molecular Component of Protein
Components of proteins
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major elements

C (50~55%), H (~7%), O (19~20%), N (13~19%), S (~4%)
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trace elements

P, Fe, Cu, Zn, I, …
Chapter 1
Structure and
Function of Protein
Contents
1. 2. 3. 4. 5. 6. 7.
Chemical components Molecular structures Biological functions Structure-function relationship Physical and chemical properties Exploration of proteins Proteomics: a new frontier
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About 300 types of AAs in nature, but only 20
types are used for protein synthesis in
biological systems.
•
An amino group, a carboxyl group, an H atom and a R group are connected to a C atom.
• • •
R groups are polar: -OH, -SH, and -CONH2. R groups are highly reactive. AAs are soluble in H2O, that is, hydrophilic, but are uncharged at neutral pH (=7.0).


the most abundant biomolecules (45% of human body)
the most complex biomolecules the most diversified biological functions
What do proteins do?
Section 1
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The C atom is an optically active center.
COOH 3 N+
C
H
R
The generic structure of an alpha amino acid
L-form versus D-form isomers
L-Amino acid
+ -
H3N C H
What are proteins?

Proteins are macromolecules composed of amino acids linked together through peptide bonds.
How are about proteins?

the most widely distributed biomolecules
Cys
Sec
selenocysteine

Sec is present in several enzymes (for example glutathione peroxidases, tetraiodothyronine 5' deiodinases, glycine reductases, and some hydrogenases).

Selenocysteine and pyrrolysine are not created through a postsynthetic modification. Instead, they are introduced during protein synthesis through an unusual adaptation of the 20 common amino acids, proteins may contain residues created by modification of common residues already incorporated into a polypeptide, such as:
R groups are different in their size, charge, hydrogen bonding capability and chemical reactivity. AAs can be assorted into five main groups(1) non-polar, aliphatic; (2) polar, neutral; (3) aromatic (4) acidic; and (5) basic, on the basis of their structure and the general chemical characteristics of their R groups.
OOC
R
L-Amino acid
COO
+
R CH 3 H
H
C
NH3
Glycine Alanine
L-amino acid
§1.2 Amino Acid can be classified by R Group
•
•
The R groups, also called side chains, make each AA unique and distinctive.

4-hydroxyproline 5-hydroxylysine -carboxyglutamate 6-N-Methyllysine




Proteinogenic amino acid

Amino acids that are precursors to proteins, and are incorporated into proteins during translation. Twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids. Selenocysteine , pyrrolysine and N-formylmethionine
OOC
H
Special amino acids - Pro

Having a ring structure and imino group
CH2 CH2 CH2 CHCOONH2+
Special amino acids - Cys
• active thiol groups to form disulfide bond

Sec is encoded in a special way by a UGA codon, which is normally a stop codon.
selenocysteine

When cells are grown in the absence of selenium, translation of selenoproteins terminates at the UGA codon, resulting in a truncated, nonfunctional enzyme. The UGA codon is made to encode selenocysteine by the presence of a selenocysteine insertion sequence (SECIS) in the mRNA. The SECIS element is defined by characteristic nucleotide sequences and secondary structure base-pairing patterns.