Cells and Their
Housekeeping
Functions – Nucleus and
Other Organelles
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
Chloroplasts, Cell Wall, and Vacuole
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Chloroplasts: green organelles that make food, found only in green
plant cells  Convert energy of light into chemical energy
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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
Chloroplasts
Cell wall
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From Cell to Organism
Cell
The basic unit of life
Tissue
Group of cells working together
Organ
Group of tissues working together
Organ System
Group of organs working together
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Organism
Any living thing made of 1 or more cells
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1- Nucleus
2- Chromosomes
3- Mitochondria
4- Ribosomes
5- Chloroplasts
6- Vacuoles
7- ER
8- Cell Membrane
Nucleus
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Largest organelle within the cell, containing DNA
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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
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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
DNA molecules are packed around and attached to beadlike protein structure (histon)
 Nucleosomes
http://en.wikipedia.org/wiki/Chromosome
Chromatin  Chromosome
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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
Protein Synthesis-1
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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
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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: energyconsuming process and driven
by energy-released by ATP
hydrolysis
Protein Synthesis-2
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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
 Excised intron transcripts rapidly
interface , mediate excision, and anneal degrade in nucleus to provide raw material
ends of exons
for new transcripts
Ribosomes
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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
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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 adapter
and matching each codon on mRNA with amino acid
the codon prescribes.
tRNAs: amino-acid-specific adapter molecules
Ribosome has binding sites for 2 different tRNA
molecules so that 2 amino acids joined to the growing
polypeptide chain at one time.