southeast university genetic center

第二章 生命的基本单位第二章 生命的基本单位 -------- 细胞细胞The basic unit of life----cellThe basic unit of life----cell

第一节 细胞的基本特性第一节 细胞的基本特性1.1 The basic conception of cell 1.1 The basic conception of cell 1.2 The size and shape of cell1.2 The size and shape of cell1.3 The prokaryotic and eukaryotic cell1.3 The prokaryotic and eukaryotic cell

第二节 细胞的物质基础第二节 细胞的物质基础2.1 2.1 Inorganic substances 2.2 2.2 Macromolecular components of Cells

Robert Hooke observed cells of a cork tree through a primitive microscope(1665)

1.1 The basic conception of cell1.1 The basic conception of cell

How to understand cell is the basic

unit Of life structure and function?

A. The Cell Is The Structural Unit Of Life, All Organisms Is Made Up Of Cells.

B. The Cell Is The Functional Unit Of Organisms. All Metabolic Activity Is Based On Cells.

C. The Cell Is The Foundation Of Reproduce and The Bridge Of Inheritance.

D. The cell is the growing and developing basis of life

1.21.2 The size and shape of cellThe size and shape of cell细胞的大小、形态细胞的大小、形态

Morphological Diversity

Rod-Shaped Bacterium, hemorrhagic E. coli (SEM x22,810)

1.3 The prokaryotic and eukaryotic cell1.3 The prokaryotic and eukaryotic cell

Differences between Prokaryotes and Eukaryotes

Prokaryotes EukaryotesSize 1-10 microns 10-100 micronsComplexity Unicellular Sometimes unicellular , m

ore often multicellularMembrane bound organelles

None (mesosome is infolding of cytoplasmic membrane)

nucleus, mit, chl, lysosomes, ER, Golgi, vacuoles

Nucleus no yesChromosome Single and circular several and linearIntrons & Exons

occasionally frequent

Histones no yesPloidy haploid DiploidMitosis & meiosis

absent present

Ribosomes 70s(50s + 30s subunits) s (sedimentation coefficient)

80s(60s + 40s)(mitochondria & chloroplasts have prokaryotic ribosomes)

Cytoskeleton absent Microtubules, microfilamemts, intermediate filaments

Cell wall Usually present Absent in animals, present in fungi and plants (cellulose)

Differentiation Usually absent Cells differentiate to form tissue & organs

Energy metabolism

Many pathways in various bacteria

Glycolysis in cytoplasm, Electron Transport Chain (ETC) in mitochondria

Endocytosis& cytoplasmic streaming

absent present

2.1 Inorganic substances ( 无机物）水 (water)无机盐 (inorganic salt) 和离子 (ion)有机小分子 (small organic molecules)

1. 糖 (sugar)

2. 脂肪酸 (fatty acid)

3. 氨基酸 (amino acid)

4. 核苷酸 (nucleotide)

第二节 细胞的物质基础第二节 细胞的物质基础 The material basis of cell

2.2.1 Carbohydrates Are Energy Sources for Cells

2.2.2 Lipids Are Components of Cell Membranes

2.2.3 Proteins Are Large Polymers of Amino Acids

2.2.4 Nucleic Acids Are the Principal Informational Molecules

2.2 Macromolecular components of Cells ( 生物大分子 )

第二节 细胞的物质基础第二节 细胞的物质基础 The material basis of cell

Monosaccharides (single unit sugars)Disaccharides (two unit sugars)Oligosaccharides(3-50 unit sugars)Polysaccharides

(hundreds or thousands unit sugars)

2.2.1 2.2.1 糖是细胞的能量来源糖是细胞的能量来源Carbohydrates Are Energy Sources for CellsCarbohydrates Are Energy Sources for Cells

单糖　 单糖　 simple sugars

Formation of a Formation of a disaccharidedisaccharide by condensation by condensation and structure of two common disaccharidesand structure of two common disaccharides

Three important disaccharideThree important disaccharide

Maltose( 麦芽糖 ) condense by two

glucose units

Lactose( 乳糖 ) condense by galactose

and glucose

Sucrose( 蔗糖 ) condense by fructose

and glucose

Polysaccharides ： Images of starch (top), glycogen (middle), and cellulose (bottom)

Glycogen

Starch

Cellu

lose

2.2.2 2.2.2 脂是细胞膜的主要成分脂是细胞膜的主要成分 Lipids Are Components of Cell MembranesLipids Are Components of Cell Membranes

Lipids have three main roles in cells:Energy Storage 　 Fatty Acids Are Stored In The Form Of Fa

ts, Which Consist Of Three Fatty Acids Linked To A Glycerol Molecule.

Components Of Cell Membranes Phospholipids ; Glycolipids ; CholesterolMessenger Molecules Most Of Them Are Derivatives Of Choleste

rol ,For Example Cortisol( 甾醇） and Testosterone （睾丸激素） .

PhospholipidPhospholipid

steroids

Saturated and unsaturate fatty acids

磷脂磷脂 (Phospholipid)(Phospholipid)

Lipids Are Components of Cell Membranes

2.2.3 2.2.3 蛋白质是氨基酸的聚合物蛋白质是氨基酸的聚合物Proteins Are Large Polymers of Amino AcidsProteins Are Large Polymers of Amino Acids

Amino acidsPeptide bond and polypeptides Protein functions

Structure of an amino acid

Each Amino Acid Consists Of – A Carboxyl Group (COO-), – An Amino Group (NH3+)– A Hydrogen Atom – Distinctive Side Chain: unique to each type

of Amino Acid

Amino acidsAmino acids

Formation of a peptide bond in a dipeptide

Four levels of protein structure

蛋白质一级结构Protein structure － primary

Amino acid sequence

蛋白质二级结构Protein structure Protein structure －－ SecondarySecondary

α-helix:• right-handed• 3.6 aa per turn• hydrogen bond N-H···O=C

β -sheet: hydrogen bonding of the peptide bond N-H and C=O groups to the complementary groups of another section of the polypeptide chain.

Secondary structure

α-helix β-pleated sheet

蛋白质三级结构蛋白质三级结构Protein structure Protein structure －－ tertiarytertiary

The different sections of -helix, -sheet, other minor secondary structure and connecting loops of a polypeptide fold in three dimensions

蛋白质四级结构蛋白质四级结构Protein structure Protein structure －－ quaternaryquaternary

Many proteins are composed of two or more polypeptide chains (subunits). These subunits may be identical or different. The same forces hold these subunits together.

1-yellow; 1-light blue; 2-green; -dark blue; heme-red

Quaternary structure of hemoglobin Hemoglobin ( 血色素四级结构 )

The functions of protein

2.2.4 2.2.4 核酸为主要的信息分子核酸为主要的信息分子Nucleic Acids Are the Principal Informational Nucleic Acids Are the Principal Informational

MoleculesMolecules

Nucleoside and nucleotide

Two forms of nucleic acidRNA( ribonucleic acid)DNA (deoxyribonucleic acid)

Nucleoside and nucleotideNucleoside and nucleotide

A mononucleotide – One Nitrogen-containing Base– One Pentose Sugar – One Phosphate Residue Derived From

phosphoric acidno phosphate group present the sugar-base

combination is called nucleoside.

pentose

phosphatebase

A T G C UOne to Three

OH

BASES NUCLEOSIDES NUCLEOTIDES

Adenine(A) Adenosine Adenosine 5’-triphosphate (ATP)

Deoxyadenosine Deoxyadenosine 5’-triphosphate (dATP)

Guanine(G) Guanosine Guanosine 5’-triphosphate (GTP)

Deoxy-guanosine Deoxy-guanosine 5’-triphosphate (dGTP)

Cytosine(C) Cytidine Cytidine 5’-triphosphate (CTP)

Deoxy-cytidine Deoxy-cytidine 5’-triphosphate (dCTP)

Uracil(U) Uridine Uridine 5’-triphosphate (UTP)

Thymine (T)

Thymidine/

deoxythymidine

Thymidine/deoxythymidine

5’-triphosphate (dTTP)

Comparison of bases, nucleosides and nucleotides

碱基Nitrogenous bases

Bicyclic purines:

Monocyclic pyrimidine:

Thymine (T) is 5-methyluracil (U)

核苷 核苷 (Nucleosides)(Nucleosides)

In nucleic acids, the bases are covalently attached to the 1’ position of a pentose sugar ring, to form a nucleoside

Glycosidic bond

R Ribose or 2’-deoxyribose

Adenosine, guanosine, cytidine, thymidine, uridine

核苷酸核苷酸 (Nucleotides)(Nucleotides) A nucleotide is a nucleoside with one or more phosphate groups bound covalently to 5’-position. one to three phosphates may be attached.

Phosphate diester bonds

Deoxynucleotides (deoxyribose containing)

Ribonucleotides (ribose containing)

Nucleotides chainNucleotides chain

DNA/RNA sequence:From 5’ end to 3’ endExample:5’-TCAGGCTA-3’= TCAGGCTA

DNA 双螺旋 (DNA double helix)

•Antiparellel •Base pairing: hydrogen bonding that holds two strands together• Sugar-phosphate backbones, negatively charged: outside•bases: inside

Watson and Crick,1953

Watson and Crick

碱基通过氢键配对碱基通过氢键配对Base pairing via hydrogen bondsBase pairing via hydrogen bonds

Hydrogen bonds

Hydrogen bonds

A-T A-T G-CG-C

Double helix

•B form:

Right-handed

10 base pairs/turn

3.4 nm /turn

Diameter: 2.0nm

Small groove

large groove

A: 11 bases/turn, Right-handed,2.6nmZ: 12 bases/turn, left-handed helical, one groove

RNARNA

Ribonucleic acids (RNA) Three forms

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Transfer RNA (tRNA)Transcription: from DNA to RNA

The function of different RNA forms in The function of different RNA forms in protein synthesisprotein synthesis

Messenger RNA (mRNA) brings this RNA information out of the nucleus to the ribosomes where translation will occur.

Transfer RNA (tRNA) reads 3 base pair units (codons) from the mRNA and brings the corresponding amino acid to the growing polypeptide chain (this process is translation).

Ribosomal RNA (rRNA) is one of the components of ribosome.

GENETIC CODE TABLE

degenerate codon

Structure Structure of of a RNA moleculea RNA molecule

RNA Secondary StructureRNA Secondary Structure

Single stranded: no long helical structure like double-stranded DNA Globular conformation: with local regions of helical structure formed by intramolecular hydrogen bonding and base stacking.

tRNAtRNA的结构的结构

The information flow in the cell

细胞内信息传递过程