1. Cell Structure
Grade 12 Biology

2. Cell Theory
All organisms are composed of one or more cells.
Cells are the smallest living units of all living organisms.
Cells arise only by division of a previously existing cell.

3. single circular molecule of DNA in prokaryotes
Cell Characteristics
Genetic material
single circular molecule of DNA in prokaryotes
double helix located in nucleus in eukaryotes – nuclear envelope (double membrane
Cytoplasm fills cell interior –
sugars, amino acids,
proteins - organelles
Plasma membrane encloses
the cell – phospholipid bilayer
Phospholipid
Membrane
proteins

4. Generalized Eukaryotic Cell

5. Cell Size
Most cells are relatively small because as size increases, volume increases much more rapidly.
longer diffusion time

6. Visualizing Cells
Resolution - minimum distance two points can be apart and still be distinguished as two separate points
Compound microscopes - magnify in stages using multiple lenses
Transmission electron microscope - electrons transmitted through specimen
Scanning electron microscope - electrons beamed onto surface of the specimen

7. Visualizing Cells

8. Prokaryotic Cells Simplest organisms
Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall composed of peptidoglycan.
no distinct interior compartments
gram-positive – thick single layer wall that retains a violet dye from Gram stain procedure
gram-negative – multilayered wall does not retain dye
Susceptibility of bacteria to antibiotics depends on cell wall structure.

9. Some use flagellum for locomotion
Prokaryotic Cells
Some use flagellum for locomotion
threadlike structures protruding from cell surface
Bacterial cell wall
Rotary
motor
Flagellin
Sheath

10. Eukaryotic Cells
Characterized by compartmentalization by an endomembrane system, and the presence of membrane-bound organelles.
Central vacuole – plants, storage
Vesicles (smaller)
Chromosomes - DNA and protein
Cytoskeleton (internal protein scaffolding)
Cell walls – plants and fungi

13. Nucleus
Repository for genetic material
Directs activities of the cell
Usually single, some cells several, RBC none
Nucleolus - region of intensive ribosomal RNA synthesis
Surface of nucleus bound by two phospholipid bilayer membranes
nuclear membrane
Nuclear pores – protein gatekeepers
Usually proteins going in and RNA going out

14. Nucleus

15. Chromosomes
DNA of eukaryotes is divided into linear chromosomes.
exist as strands of chromatin, except during cell division
associated with packaging histones, packaging proteins
nucleosomes

16. Endomembrane System
Compartmentalizes cell, channeling passage of molecules through cell’s interior.
Endoplasmic reticulum
Rough ER - studded with ribosomes
Smooth ER - few ribosomes

17. Endoplasmic reticulum
Largest internal membrane
Composed of Lipid bilayer
Serves as system of channels from the nucleus
Functions in storage and secretion
Rough ER is “rough” because of associated ribosomes (sites of protein synthesis
Smooth ER - lack associated ribosomes – contained embedded enzymes, catalyze synthesis of carbohydrate and lipid molecules

18. Endomembrane System Golgi apparatus collection of Golgi bodies
collect, package, and distribute molecules synthesized at one location in the cell and utilized at another location
Front - cis , Back – trans
Cisternae – stacked membrane folds

19. Cisternae cis face Proteins trans face Protein Ribosome
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Cisternae
cis face
Proteins
trans face
Transport
vesicle
Golgi
apparatus
Protein
Vesicle
budding
from rough
endoplasmic
reticulum
Migrating
transport
vesicle
Fusion
of vesicle
with Golgi
apparatus
Ribosome

20. Endomembrane System
Vesicles
Lysosomes - membrane-bound vesicles containing digestive enzymes – from Golgi
Microbodies - enzyme-bearing, membrane-enclosed vesicles.
Peroxisomes - contain enzymes that catalyze the removal of electrons and associated hydrogen atoms
Peroxisome – named for hydrogen peroxide produced as a by-product
Enzyme breaks down to water and oxygen

21. Cytoplasm Extracellular fluid
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Cytoplasm
Endoplasmic
reticulum
Phagocytosis
Food
vesicle
Golgi
apparatus
Lysosomes
Transport
vesicle
Old or damaged
organelle
Plasma
membrane
Digestion of
phagocytized
food particles
or cells
Breakdown
of old
organelle
Extracellular
fluid

22. Ribosomes
Ribosomes are RNA-protein complexes composed of two subunits that join and attach to messenger RNA.
site of protein synthesis
assembled in nucleoli

23. Organelles With DNA
Mitochondria
bounded by exterior and interior membranes
interior partitioned by cristae
Chloroplasts
have enclosed internal compartments of stacked grana, containing thylakoids
found in photosynthetic organisms

24. Mitochondria
A. "Powerhouse of the cell" - cellular metabolism
B. Structure- outer and inner membranes, cristae
C. Have their own DNA

25. Chloroplasts
Chloroplasts are larger and more complex than mitochondria
Grana – closed compartments of stacked membranes
Thylakoids – disc shaped structure – light capturing pigment
Stroma – fluid matrix

26. Endosymbiosis
Endosymbiotic theory suggests engulfed prokaryotes provided hosts with advantages associated with specialized metabolic activities.

27. Theory of Endosymbiosis

28. Evidence for the endosymbiont theory is that mitochondria and chloroplasts:
- Are appropriate size to be descendants of eubacteria.
- Have inner membranes similar to those on prokaryotic plasma membranes.
- Replicate by splitting, as in prokaryotes.
- DNA is circular and different from the DNA of the cell's nucleus.
- Contain their own components for DNA transcription and translation into proteins .
- Have ribosomes similar to prokaryotic ribosomes.
- Molecular systematics lend evidence to support this theory.
- Many extant organisms are involved in endosymbiotic relationships.

29. Cytoskeleton
Network of protein fibers supporting cell shape and anchoring organelles
Actin filaments
cell movement
Microtubules
Hollow tubes
Facilitate cell movement
Centrioles – barrel shaped
organelles occur in pairs –
help assemble animal cell’s microtubules
Intermediate filaments
Stable - don’t break down
Actin
Microtubules
Intermediate
filaments

30. Cytoskeleton

31. Plant Cells
Central vacuole
often found in the center of a plant, and serves as a storage facility for water and other materials
Cell wall
primary walls – laid down while cell is growing
middle lamella – glues cells together
secondary walls – inside the primary cell walls after growth

32. Plant Cell

33. Animal Cells
Animal cells lack cell walls.
form extracellular matrix
provides support, strength, and resilience