cellls

1. Cells and organelles
Lecture 4
Chapter 4
30/ 10/2021
Lecture 4 cells & organelles

2. The Endomembrane System
Synthesizes Proteins for a Variety of
Cellular Destinations
• The endomembrane system (Endoplasmic
reticulum, vesicles, vacuoles……) synthesizes
proteins destined for various organelles,
cellular membranes, or secretion
• The proteins are packaged and then directed
to various destinations around the cell in small
membrane-bound vesicles
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3. © 2017 Pearson Education, Ltd.

4. Rough Endoplasmic Reticulum
• ER can be rough or smooth in appearance
• Rough ER is studded with ribosomes on the
cytoplasmic side of the membrane
• These ribosomes synthesize polypeptides that
accumulate within the membrane or are
transported across it to the lumen
• Free ribosomes are not associated with the ER
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5. Smooth Endoplasmic Reticulum
• Smooth ER has no role in protein synthesis
• It is involved in the synthesis of lipids and
steroids such as cholesterol and its derivatives
• Smooth ER is responsible for inactivating and
detoxifying potentially harmful substances
• Sarcoplasmic reticulum has critical functions
in contraction
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6. The Golgi Apparatus
• The Golgi apparatus, closely related to the ER
in proximity and function, consists of a stack
of flattened vesicles known as cisternae
• It plays an important role in processing and
packaging secretory proteins, and in synthesis
of complex polysaccharides
• It accepts transition vesicles that bud off the
ER
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7. © 2017 Pearson Education, Ltd.

8. Golgi complex
Lecture 4 cells & organelles
Involved in
1. processing,
sorting and
packing of
secretory
proteins.
2. Synthesizing
polysaccharides

9. © 2017 Pearson Education, Ltd.

10. Lysosome
Lecture 4 cells & organelles
Lysosomal enzymes are synthesized on the rough
ER, transported to Golgi bodies, packed into vesicles
forming lysosomes.

11. Lysosome
Lecture 4 cells & organelles
Surrounded by a single membrane
Phagocytosis: lysosome digesting food
Lysosome contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Digestion
Food vacuole
Plasma membrane
Lysosome
Digestive
enzymes

12. Functions of Lysosomes
Lecture 4 cells & organelles
a. contains hydrolytic enzymes
(1) phosphatases
(2) nucleases
(3) proteases
(4) lipases and lots other hydrolytic
enzymes

13. Functions of Lysosomes
Lecture 4 cells & organelles
b. recycling organelle
(1) breaks down large
molecules to building
block subunits.
(2) subunits reused by cell.
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Vesicle containing
damaged mitochondrion
Digestion
Lysosome

14. Functions of Lysosomes
Lecture 4 cells & organelles
c. feeding organelle
(1) cell ingests macromolecules, breaks
down macromolecules to building blocks
molecules such as amino acids, sugars,
etc

15. Vacuoles
Lecture 4 cells & organelles
many types
a. food vacuole in Protista
(1) produced during endocytosis
(2) food vacuoles fuse with lysosomes

16. Vacuoles
Lecture 4 cells & organelles
b. Contractile
vacuoles:
Controlling
the osmotic
pressure of
the cell.

17. Vacuoles
Lecture 4 cells & organelles
c. central vacuole in plants
(1) storage role for nutrients +
toxic biotic &abiotic
compounds including
defense compounds+
secondary compounds
(a) wide variety of molecules &
ions (heavy metals like
Cadmium and Arsenate
(2) lysosomal role (minor).
(3) maintenance of turgor
pressure

18. Peroxisome
Lecture 4 cells & organelles
Surrounded by a single membrane.
Peroxisomes are found in plant , animal
, fungi, protozoa and algae.
Chloroplast
Peroxisome
Mitochondrion

19. Peroxisome
Lecture 4 cells & organelles
Involved in
 The generation and degradation of hydrogen
peroxide (H2O2 ) by the action of catalase.
Detoxification of methanol, ethanol, formate
and formaldehyde.

20. Peroxisome
Lecture 4 cells & organelles
Regulation of aging process by the regulation of
oxygen levels.
Oxidative breakdown of fatty acids longer than
12 carbon atoms.

21. Lecture 4 cells & organelles

22. Peroxisome
Lecture 4 cells & organelles
In plant system;
 Specialized peroxisomes are called
glyoxysomes converting stored fats of seeds into
polysaccharides.
 Leaf peroxisomes are involved in
photorespiration.

23. Lecture 4 cells & organelles
Major functions of cytoskeleton
 Help establish and maintain cell shape.
 Positioning of actively moving organelles
 Plays an important role in cell division and cell
movement.

24. components of cytoskeleton
Lecture 4 cells & organelles
 Microfilaments
 Microtubules
 Intermediate filaments

25. Cytoskeleton
Lecture 4 cells & organelles

26. Microtubules
Lecture 4 cells & organelles
 Largest elements in cytoskeleton
 Straight, hollow cylinders
 Outer diameter = 25 nm
 Inner diameter = 15 nm
 Tubulin is dimeric protein; one alpha & one
beta subunit form the tubulin dimer

27. Microtubules- functions
Lecture 4 cells & organelles
I. axoneme found in cilia and flagella- cell
motility
II. spindle fibers- movement of chromosomes

28. Eukaryotic flagella.
1) Axoneme
2) cell membrane
3) IFT (IntraFlagellar
Transport)
4) Basal body
5) Cross section of flagella
6) Triplets of microtubules of
basal body.
Lecture 4 cells & organelles

29. 2005-2006
AP Biology Lecture 4 cells & organelles

30. Microtubules- Spindle Fibers
Lecture 4 cells & organelles

31. Microfilaments
Lecture 4 cells & organelles
 Smallest major cytoskeletal component.
 Polymers of actin
 Two double helical strands F-actin
 Each strand is about 4 nm diameter
 Together about 7 nm diameter

32. functions of microfilaments
Lecture 4 cells & organelles
 Contractile fibrils of muscle cells.
 Form connections with plasma membrane
 Pinching of cleavage furrows of dividing
animal cells
 Help develop and maintain cell shape

33. Lecture 4 cells & organelles
 Microfilaments have role in cytoplasmic streaming

34. Lecture 4 cells & organelles
• interaction of actin filaments with myosin near the cell’s trailing
end squeezes the interior fluid forward into the pseudopodium
 Microfilaments have role in Amoeboid movement
Extending
pseudopodium
Inner cytoplasm: sol with actin
subunits
Cortex (outer cytoplasm): gel
with actin network

35. intermediate filaments
Lecture 4 cells & organelles
 Slightly larger than microfilaments.
 Diameter of 8-12 nm.
 Most stable of the three filaments.

36. intermediate filaments
Lecture 4 cells & organelles
 Least soluble of the three filaments.
 Probably the primary support for whole
cytoskeleton
 Differ in composition from cell to cell-different
gene products

37. Extracelullar matrix- cell wall
Lecture 4 cells & organelles
 Found in Kingdoms of planta, monera, fungi,
protista.
 Plant cell walls made of cellulose.
 Rigid structure.
 Not part of living protoplasm.

38. Extracelullar matrix- cell wall
Lecture 4 cells & organelles
have cytoplasmic bridges connecting adjacent cells-
plasmodesmata between plant cells
Interior
of cell
Interior
of cell
0.5 µm Plasmodesmata Plasma membranes
Cell walls
Figure 6.30

39. Viruses
Lecture 4 cells & organelles
Are viruses living cells???????
Fundamental properties of living things:
Metabolism
Irritability
Reproduction

40. What are Viruses?
• A virus is a non-cellular particle
made up of genetic material and
protein that can invade living cells.
Lecture 4 cells & organelles

41. Characteristics of viruses
 None living structures
 None cellular
 Contain a protein coat called the capsid
 Have a nucleic acid core containing DNA or RNA
 Capable of reproducing only when inside a HOST cell
Lecture 4 cells & organelles

42. Viruses
Lecture 4 cells & organelles
 Size 1. 25 to 300 nm.
 Smallest about size of ribosome.
 Largest about 1/4 size bacterial cell.
Tobacco mosaic virus

43. Size of Viruses
Lecture 4 cells & organelles

44. Viruses
Lecture 4 cells & organelles
Each virus has characteristic shape.
 Special proteins complexed together as "coat"
surrounding some specific nucleic acids (DNA or
RNA

45. Viroids
Lecture 4 cells & organelles
1. Smaller than viruses.
2. Naked circular RNA.
3. 300 to 400 nucleotides long.

46. Viroids
Lecture 4 cells & organelles
4. Don't code for protein.
5. Cause disease in plants (Cadang cadang disease of
coconut).
6. No membrane barrier for the RNA molecule to cross.
7. Transmitted by seed, pollen and agricultural practices.
8. Possibly cause gene silencing.

47. Prions
Lecture 4 cells & organelles
Cause disease in animals
 Scrapie in sheep
 "Mad Cow" disease

48. Prions
Lecture 4 cells & organelles
 Caused by "proteinaceous infective particles =
prions"
 Probably a protein affects transcription or
protein processing such producing a different form
of protein instead of the protein normally
produced by cell.

49. Prion Diseases
 Prions form insoluble
deposits in the brain.
 Causes neurons to rapidly
degenerate.
 Mad cow disease (bovine
spongiform encephalitis:
BSE) is an example.
 People in New Guinea used
to suffer from kuru, which
they got from eating the
brains of their enemies
Lecture 4 cells & organelles

50. Prions
Lecture 4 cells & organelles
 Both normal and variant forms protein were
found on the surface of nerve cells.
 Variant proteins might affect receptors that
detect nerve signals leading to symptoms.