Download The cell

Introduction to Biology
September 17th 2004
Nancy Van Driessche (email:
[email protected])
Overview of “What is a cell?”:
http://www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html
What is a cell?
●
structural and functional units of all living organisms
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unicellular and multicellular organisms
–
bacteria vs. human
specialized functions
nutrients
energy source
reproduce
Eukaryote vs. Prokaryote
eg. fungi
eg. bacteria
animals
plants
unicellular organisms: yeast, Dictyostelium etc.
Biggest differences: Prokaryotes lack a nuclear membrane!
Prokaryotes don't have intracellular organelles!
Prokaryotes about 10X size of Eukaryotes.
Plasma membrane: a cell's protective
coat
outside the cell
double layer of lipids
proteins
inside the cell
Several functions of membrane proteins:
outside the cell
inside the cell
inport and export cross-linking of
of molecules membrane proteins amplification of convertion of product
extracellular signal X into product Y
The cytoskeleton: a cell's scaffold
●
●
●
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very complex and dynamic cell component!
organizes and maintains the cell's shape (e.g.
epithelial cells of the gut)
anchors the organells in place
helps during the uptake of external material
(endocytosis)
●
involvement in cell movement
●
growth
The cytoskeleton: a cell's scaffold
The cytoplasm (cytosol): a cell's inner
space
Plasma
membrane
Cytoskeleton
cytosol
large fluid-filled space (mostly water + proteins that control most of th
cell metabolisms):
glycolysis, transcription factors, intracellular receptors etc.
Organelles
●
Nucleus
●
Protein production machine: the ribosomes
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Mitochondria and Chloroplasts
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Endoplasmic Reticulum and the Golgi
apparatus
Lysosomes and Peroxisomes
Adapted and/or specialized for carrying out one or more vital functions.
Reminder! Are only found in eukaryotes.
Nucleus: a cell's center
Structure of the nucleus:
Function of the nucleus:
- Stores the chromosomes (genetic
material)
Note: 2 kinds of genetic material:
deoxyribonucleic acid (DNA)
ribonucleic acid (RNA)
- production of ribosomes in nucleolus
- protection of DNA from damaging
molecules of molecules that interfere
with its processing
- DNA replication and synthesis of
messenger RNA (mRNA)
source: http://cellbio.utmb.edu/cellbio/nucleus.html
Endoplasmic Reticulum and the
Ribosomes: protein production
machine
Endoplasmic Reticulum (ER)
source: http://cellbio.utmb.edu/cellbio/ribosome.htm
Endoplasmic Reticulum
ER is a continuation of the outer nuclear membrane.
ER has smooth regions (responsible for lipid and membrane
protein modifications) and rough regions (associated with
ribosomes responsible for the synthesis of other proteins)
source: http://www.cellsalive.com/cells/er.htm
Golgi apparatus
Function:
- modification of lipids and proteins
- storage and packaging of materials that will be exported from the cell.
source: http://cellbio.utmb.edu/cellbio/golgi.htm
Mitochondria
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Contain their own genome
(distinct from nuclear
genome)
Self-replicating
Critical role in generation of
energy (called ATP):
Glycolysis (without oxygen
use)
Kreb’s cycle (in presence of
oxygen)
Lysosomes
●
Rich in digestive enzymes (that work at low
pH)
●
Digest fforeing bacteria that invade a cell
●
Recycling of membrane components
●
Repair damage to plasma membrane
Peroxisomes
●
Get rid of toxic substances
●
Many in the liver
lysosome
Making new Cells and Cell types
(1) Making New Cells
Unicellular organisms:
Asexual reproduction: replication of genetic material and splitting 1 cell
Into 2 identical cells
Multicellular organisms:
Mitosis to produce for example new skin cells and liver cells.
Meiosis or sexual reproduction to create a whole new organism (gametes)
Human chromosomes
Overview of the major events in mitosis
Interphase
prophase
metaphase
anaphase
telophase
In case of DNA damage or failure of critical processes
P53 stimulates induction of inhibitory
proteins that halt DNA replication
Defects in p53 are associated with a
variety of cancers
DNA damage repair or initiation of programmed cell death (apoptosis)
Overview of the major events in meiosis
Production of gametes
2 cell divisions in sequence
Big difference between mitosis and meiosis
The Working Cell
DNA, RNA and Protein Synthesis
DNA structure – base pairs
adenosine
thymine
cytosine
guanine
Source: http://www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML
DNA – The code of life
Side view:
3’ end
5’ end
Double stranded
AT – GC basepairs
Right handed spiral
View down helix axis:
3’ end
5’
Source: http://www.blc.arizona.edu/Molecular_Graphics/DNA_Structure/DNA_Tutorial.HTML
DNA replication
Occurs during cell division.
Requires:
- Helicases (unwind DNA)
- DNA polymerases (can bind single
Stranded DNA and can move only
In 3’ to 5’ direction.
- DNA ligase stitches Okazaki fragments
Source: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html
Animation:
http://www.phschool.com/science/biology_place/biocoach/dnarep/repstrands.html?blah=&step=6
Transcription: RNA synthesis
Basic structure of a protein encoding gene:
DNA
Transcription: RNA synthesis
(1) Initiation
- Involves transcription factors (TFs) and
RNA polymerase
- Recognition of TATA box (located ~ 20
to 30 bp of transcription initiation site)
Transcription (elongation) (2)
/antisense strand
Transcription (termination) (3)
RNA polymerase falls off
terminator
Animation:
http://www.phschool.com/science/biology_place/biocoach/images/transcription/tcani.gif
DNA vs. RNA
Post-transcriptional modifications
Protein synthesis: Translation initiation
Protein synthesis:
elongation (2)
Protein translation:
termination (3)
Protein translation: summary
Elongation
Initiation
Termination
http://www.phschool.com/science/biology_place/biocoach/translation/init.html
Summary