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Presentation on theme: "THE CYTOSKELETON AND RELATED STRUCTURES"— Presentation transcript:

The cell’s internal skeleton helps organize its structure and activities A network of protein fibers make up the cytoskeleton. Actin subunit Microfilament 7 nm Fibrous subunits 10 nm Intermediate filament Microtubule 25 nm Tubulin subunit

2 Microfilaments of actin Intermediate filaments
Enable cells to change shape and move Intermediate filaments Reinforce the cell and anchor cer tain organelles Microtubules give the cell rigidity And provide anchors for organelles and act as tracks for organelle movement

3 A typical plant cell has some structures that an animal cell lacks
Such as chloroplasts and a rigid cell wall Central vacuole Not in animal cells Chloroplast Cell wall Golgi apparatus Nucleus Microtubule Cytoskeleton Intermediate filament Microfilament Ribosomes Smooth endoplasmic reticulum Mitochondrion Peroxisome Plasma membrane Rough endoplasmic reticulum Figure 4.4B

4 Plant cells Are suppor ted by rigid cell walls made largely of cellulose Connect by plasmodesmata, which are connecting channels Plasma membrane Cytoplasm Plasmodesmata Vacuole Layers of one plant cell wall Walls of two adjacent plant cells Figure 4.18A

5 Tight junctions can bind cells together into leakproof sheets
Anchoring junctions link animal cells into strong tissues Gap junctions allow substances to flow from cell to cell Anchoring junction Tight junctions Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells Figure 4.18B

6 Human Organelle Diseases/Problems

7 Cystic Fibrosis and the Cell Membrane
Cystic fibrosis (CF) is caused by a salt imbalance, making mucus in the lungs and digestive system extremely thick. Caused by recessive gene; about 20% of us are carriers Several new treatments, including a healthy gene introduced into the lungs in a nasal spray, target the illness at the cellular source. Source:

8 Adrenoleukodystrophy (ALD) and Peroxisomes
Cause: peroxisomes lacked the second most abundant protein in the outer membrane of this organelle. Normally, the missing protein (a chaperone protein) transports an enzyme into the peroxisome. Without the enzyme, fatty acids builds up in cells in the brain and spinal cord, eventually myelin is depleted (vital for nerve transmission). Death comes in a few years. For many sufferers of ALD, eating a type of triglyceride from rapeseed (canola) oil slows buildup of the very long chain fatty acids for a few years, stalling symptoms. But the treatment eventually impairs blood clotting and other vital functions, and fails to halt the progression of the illness.


10 Tay-Sachs Disease and Lysosomes
More common in some ethnic communities, a mutation of an enzyme in lysosomes In eyes, a telltale cherry red spot indicates the illness the lysosomes, tiny enzyme-filled sacs, swell to huge proportions. These lysosomes lack one of the forty types of lysosomal enzymes, results in built up fatty material on nerve cells. Sadly and commonly, the nervous system continues to fail, and paralysis , then death before the age of four.


12 Cystic Fibrosis & the Rough ER
a prominent example of a disease caused by misfolded proteins. CF is an ultimately fatal inherited disorder in which the lack of a specific type of plasma membrane chloride channel, the cystic fibrosis transmembrane regulator (CFTR), causes the accumulation of a thick mucus that compromises several organs, most notably the lungs and pancreas. The misfolded CFTR protein becomes trapped within the ER and is subsequently degraded. Source:

13 ER stress induced by a variety of conditions such as proteinaggregation, Ca2 depletion, glucose deprivation, or fatty acid overload, can result in severe cell dysfunction or death. It is an important feature of such neuro-degenerative conditions as Alzheimer’s, Huntington’s, and Parkinson’s diseases, as well as heart disease and diabetes.


15 GOLGI APPARATUS The most commonly recognized Golgi-linked diseases are a group of 15 congenital disorders of glycosylation (CDG). Caused by mutations in genes that encode glycosylation enzymes or glycosylation-linked transport proteins a CDG is usually lethal by the age of 2. Symptoms include mental retardation, seizures, and liver disease.

16 Nuclear Membrane problems
defects in the nuclear envelope occur in the genes that code for lamin, a cytoskeletal component of the nuclear lamina, and emerin, an inner membrane protein.

17 1. Progeria a fatal childhood disease characterized by premature aging of the musculoskeletal and cardiovascular systems Has been linked to a specific mutation in the lamin A gene.

18 2. Emery-Dreifuss muscular dystrophy
caused by the absence or mutation of the gene that codes for emerin Symptoms include: a fragile nuclear membrane altered regulation of DNA replication and transcription and low tolerance to mechanical stress.

19 Lysosomes & Peroxisomes
lysosomal storage diseases (LSD) caused by the absence of one or more lysosomal enzymes Examples: Tay-Sachs and Gaucher’s, as well as Pompe’s disease (glycogen storage disease type II), are caused by the absence of a single enzyme. Death occurs in early childhood. In I-cell disease, the import of all lysosomal enzymes into lysosomes in certain organs is defective. In affected cells, the enzymes are instead secreted into the extracellular matrix. Symptoms include mental deterioration, heart disease, and respiratory failure.

20 Mitochondrial problems
High rates of mutation, since it is an ancient bacterium Mutation in proteins that guide mitochondrial division create dissimilar daughter mitochondria This increases risk of inheriting mutations that are harmful to mitochondrial function. Examples: exercise intolerance, chronic fatigue Examples: diabetes, Parkinson’s, Alzheimer’s

21 © 2005 Nature Publishing Group Taylor, R. W. et al
© 2005 Nature Publishing Group Taylor, R. W. et al. Mitochondrial DNA mutations in human disease. Nature Reviews Genetics 6, 394 (2005). All rights reserved.

22 Mitochondria & Cancer? In 1998, a link between colorectal cancer and somatic mitochondrial mutations was established by Polyak and colleagues. These researchers cultured colorectal cancer cells taken from the tumors of 10 colorectal cancer patients, and found significant mitochondrial mutations not present in nearby tissues samples. Conclusion: perhaps mutated mitchondrial enable enhanced ATP production needed by cancer cells for fast reproduction?

23 MtDNA accumulates mutations rapidly
mtDNA accumulates mutations approximately 10 times faster than nuclear DNA. Why?: repair mechanisms present in the nucleus are absent in mitochondria mitochondria produce oxygen free radicals that can oxidize DNA and RNA (usually producing mutations) mtDNA lacks histones proteins , which are thought to protect DNA from damage

24 The Inner Life of the Cell
The Harvard Cell Video The XVIVO Version of the Video


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