Shu-Ping Lin, Ph.D.

Institute of Biomedical Engineering E-mail: splin@dragon.nchu.edu.tw

Website: http://web.nchu.edu.tw/pweb/users/splin/

Date: 10.27.2010

Cells and Their Housekeeping

Functions – Nucleus and Other Organelles

Chloroplasts: green organelles that make food, found only in green plant cells Convert energy of light into chemical energy

Chlorophyl: green pigment that gives leaves & stems their color Captures

sunlight energy that is used to produce food called glucose (Glucose is a type of sugar)

Cell wall: restrict shape change and mobility

Vacuole: collect and store nutrient molecules and waste products

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Chloroplasts, Cell Wall, and Vacuole

Cell wall

Chloroplasts

From Cell to Organism

CellThe basic unit of life

TissueGroup of cells working together

OrganGroup of tissues working together

OrganismAny living thing made of 1 or more cells

Organ SystemGroup of organs working together

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1- Nucleus

2- Chromosomes

3- Mitochondria

4- Ribosomes

5- Chloroplasts

6- Vacuoles

7- ER

8- Cell Membrane

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Nucleus Largest organelle within the cell, containing DNA

DNA replication: necessary for cell division (so that both daughter cells have identical copies of DNA)

Transcription: formation of an RNA template of a gene, essential for protein synthesis

Library of genetic information

Bounded by nuclear membrane, 2 lipid bilayers of double membrane are separated by a gap (20~ 40nm) with many openings or pores for trafficking small molecules and proteins

Chromosome

Identical sets of chromosomes(long and thin DNA molecules, store genetic information) in each eukaryote

Histone: beadlike protein structure, Ex: each human cell has about 1.8 meters of DNA, but wound on the histones it has about 90 millimeters of chromatin

Before cell division, DNA is replicated and tightly coiled and bound in identical pairs called chromatids Chromosomes

can be seen by light microscopy.

Chromatin

http://en.wikipedia.org/wiki/Chromosome

DNA molecules are packed around and attached to beadlike protein structure (histon) Nucleosomes

Chromatin Chromosome

Different levels of DNA condensation. (1) Single DNA strand. (2) Chromatin strand (DNA with histones). (3) Chromatin during interphase with centromere. (4) Condensed chromatin during prophase. (Two copies of the DNA molecule are now present) (5) Chromosome during metaphase.

http://zh.wikipedia.org/zh-tw/File:Chromatin_chromosome.png

RNA polymerase: transcribe RNA from DNA template at average rate 30 nucleotides/sec, an enzyme consisting of 12 different polypeptides with mass of 500kDa, arrange in 10 subunits RNA polymerase II (pol II): central

machine for synthesis protein of mRNA in eukaryotes

Polymerase I: ribosomal RNA, polymerase III: transfer RNA

9 out of 10 subunits are identical in these 3 enzymes

Begin in nucleus with binding of transcription factors to regulatory sequence (protein-coding gene)

Transcription: energy-consuming process and driven by energy-released by ATP hydrolysis

Protein Synthesis-1

Binding of transcription factors to regulatory sequence (protein-coding gene) on DNA ––Activate Pol II unwind DNA double helix Polymerize mRNA

and proofread the resulting transcript

Pol II recognize promoter region of genes if DNA interact with transcription factors

Subunits 1, 5, and 9 of pol II grip DNA downstream of active center

Subunits 1, 2, and 6 clamp on DNA near active center Growing mRNA strand

locks this clamp, thus stabilizing transcribing complexes

Complete RNA molecule (primary RNA transcript, pre mRNA): 20,000 nucleotides because of noncoding introns RNA splicing mRNA Transport out

of nucleus and interact with ribosomes in cytoplasm to begin translation

Spliceosome: recognize exon/intron interface , mediate excision, and anneal ends of exons

Protein Synthesis-2

Excised intron transcripts rapidly

degrade in nucleus to provide raw material for new transcripts

Ribosomes Small and darkly staining spherical

structures: ~20 nm in diameter that are made of 50 proteins and several long RNAs intricately bound together

Ribosomes are made in the nucleolus, compartment in nucleus. Once

constructed, ribosomes leave nucleus through nuclear pores.

Float freely in the cytoplasm to synthesize cytoplasmic proteins without any further modification or attach to the endoplasmic reticulum (ER) to manufacture membrane proteins

Make proteins Translate sequence information on mRNA into

polypeptides

No membrane and disassemble into 2 subunits when not actively synthesizing protein

Protein synthesis is extremely important, so eukaryotic cells contain million of ribosomes.

Take 30 sec to synthesize a protein containing 400 amino acids, and human cell synthesize 1010 proteins in 24 hr

Translation of mRNA by Ribosomes

1. Attachment of mRNA to a ribosome

2. Begin knitting together amino acids, according to template encoded mRNA

3. Translation is initiated by tRNA, acting as adapterand matching each codon on mRNA with amino acid the codon prescribes.

tRNAs: amino-acid-specific adapter molecules

Ribosome has binding sites for 2 different tRNAmolecules so that 2 amino acids joined to the growing polypeptide chain at one time.