Transcript Chapter 3 The Cell - People Server at UNCW

Cellular Aging
A. Introduction
1. The cell is the basic structural and functional unit of life
2. Four basic components
a. Cell (plasma) membrane
b. Organelles
c.
Cytoplasm
d. Inclusions
Cellular Aging
B. Cell (plasma) membrane
1. Bilayer of phospholipids
a. Hydrophilic phosphate “heads”
b. Hydrophobic fatty acid “tails”
2. Integral vs. peripheral proteins
3. Carbohydrate groups and their roles
4. Selectively permeable
Cellular Aging
C. Organelles
1. Nucleus
a. Control center of the cell
b. Houses DNA
c.
Genes transcribed into mRNA
(process of transcription)
d. mRNA moves into cytoplasm
e. mRNA is translated into protein at a
ribosome (process of translation)
Cellular Aging
C. Organelles
2. Endoplasmic reticulum
a. Network of membranous tubules
b. Smooth vs. rough ER
c.
Functions
i.
Synthesis of proteins destined for
secretion
ii.
Steroid synthesis
iii.
Detoxification
iv.
Storage
Cellular Aging
C. Organelles
3. Ribosomes
a. Granules of protein and rRNA
(ribosomal RNA)
b. Free-floating in cytoplasm or
attached to endoplasmic reticulum
(rough ER)
c.
Become associated with mRNA
during translation, giving rise to a
new protein
Cellular Aging
C. Organelles
4. Golgi apparatus (complex)
a. Stacks of flattened membranous
sacs
b. Function in packaging materials
destined for secretion
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C. Organelles
5. lysosomes
a. Membrane-bound vesicles
b. Contain strong, non-specific proteindigesting enzymes
c.
Present in all cells; very prevalent in
phagocytes and macrophages
d. Functions
Cellular Aging
C. Organelles
6. mitochondria
a. Double membrane-bound
b. Inner membrane has multiple folds
that contain “respiratory” enzymes
c.
Functions in production of energy
(ATP) from food sources
d. More prevalent in highly metabolic
cell types
Cellular Aging
C. Organelles
7. Centrioles
a. Paired cylinder-shaped arrays of
microtubules that lie at right angles
to each other
b. Involved in cell division, giving rise to
a network of tubules called the
spindle fibers
c.
Spindle fibers involved in
redistribution of chromosomes to
daughter cells
Cellular Aging
C. Organelles
8. Cytoskeleton
a. 3-D network of microfilaments and
microtubules
b. Functions
i.
Maintain cell shape
ii.
Aid in cell organization
iii.
Transport within the cell
iv.
Cell division
v.
Cellular movement
Cellular Aging
D. Validity of cell culture findings
1. Normal cells in culture lose their mitotic ability
a. They don’t die (HeLa cells)
b. But they do age like normal cells in the body
2. Mix old cells with young cells – old stop mitosis first
3. Conditioned medium experiments
4. Fibroblasts from progeria patients
5. Transplant studies
6. Cells in vitro exceed the abilities of cells in vivo
Cellular Aging
E. Specific cellular changes during aging
1. Cellular aging is generally thought to be
influenced by changes in cell functions that:
a. Alter protein synthesis
b. Reduce the efficiency of DNA repair
c.
Decrease enzymatic activity
2. All the specific cellular changes that have these
effects aren’t known
Cellular Aging
E. Specific cellular changes during aging
3. Membrane changes
a. Alterations in transport of nutrients, ions, amino acids, and
proteins
b. Loss of fluidity due to structural changes
i.
Plasma membrane – changes in permeability
ii.
Endoplasmic reticulum
iii.
Mitochondria – decreased metabolic activity
Cellular Aging
E. Specific cellular changes during aging
4. Nuclear changes
a. All changes in nuclear function would be expressed in
altered protein synthesis
b. Altered enzymes and structural proteins would lead to
altered cell functions
c.
Specific changes include:
i.
Increased DNA damage
ii.
Decreased efficiency of DNA repair processes
iii.
Increased cross-linking of DNA, leading to inaccessible
genes
Cellular Aging
E. Specific cellular changes during aging
5. Cytoplasmic changes
a. Increased volume coupled with decreased DNA synthesis
b. Build-up of lipofuscin
6. Ribosomal changes
a. Decreased total ribosomal RNA (rRNA)
b. Decreased number of ribosomes
c.
Result = decreased protein synthesis
Cellular Aging
E. Specific cellular changes during aging
7. Mitochondrial changes
a. Lipofuscin may be produced by old mitochondria
b. Reduced inner membrane folds
c.
Decreased number of total mitochondria
d. Increased dysfunction resulting from free radicals
e. Results = decreased ATP production
8. Lysosomal changes
a. Less efficient in removing cell garbage
b. Damaged lysosomes leak their enzymes, causing
cell damage/death
Cellular Aging
F. Take home messages
1. Most of the data comes from cell culture work
2. Many of the changes involve synthesis of or activities of
proteins (enzymatic and structural)
3. Specific changes that are known to occur include:
a. Membrane alterations
e. Lipofuscin accumulation
b. Increased DNA damage
f.
c.
g. Inefficient lysosomes
Decreased DNA repair
Decreased mitochondria
d. DNA cross-linking
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