Characteristics of cells

1. Characteristics of Cells
Chapter 3
Unit 1

2. Cells
Cells are the basic unit of all living things
Human body composed of approximately 75
trillion cells
Form begets function

3. Composite Cell
There are no “typical” cells in humans

4. Cell Parts
Under the light microscope…
Cell Membrane
Nucleus
Cytoplasm
*Must use a stain to see these structures

5. Stained Cells
Human Cheek Cells

6. Cell Parts
Organelles
Structures with special functions in the cell
“Little Organs”
Found in the cytosol (liquid part of cell)

7. Cell Parts
Membranes
Composed of phospholipids
Naturally form a bilayer
Nonpolar (hydrophobic) tails group in membrane
interior
Polar (hydrophilic) heads are forced to the outside
of the membrane bilayer

8. Membranes

9. Cell Parts
Plasma Membrane
Surrounds all human cells
Living & Active
Participates in signal transduction
Selectively permeable (AKA
“Semipermeable”)
Creates a barrier to keep “stuff” out
Holds cell contents in

10. Cell Parts
Plasma Membrane
Fluid Mosaic
Fluid:
Phospholipids move around each other
Lipid bilayer is always in motion
This feature ensures membrane is both stable &
flexible at same time
Mosaic
Composed of phospholipids, proteins, and
carbohydrate molecules
Membrane Features

11. Cell Parts
Plasma Membrane
Membrane Proteins
Transmembrane Proteins
Span the entire membrane
Channels for movement of specific molecules
Peripheral Proteins
Only on either the inside or outside of membrane
Anchor membrane to cyctoskeleton
Signal receptors
Markers

12. Cell Parts
Membrane Organelles
Endoplasmic Reticulum
Complex network of membranes
Transports materials throughout cell using vesicles
“Communicates” with other organelles
Rough
Protein synthesis
Studded with ribosomes
Smooth
No ribosomes
Used for breakdown of fats and various drugs/alcohol

13. Cell Parts
Membrane Organelles
Gogli Apparatus
Flat, membranous sacs
Accepts vesicles from ER containing proteins
Chemically alters and prepares proteins
Packages and sends proteins for export
Vesicles
Membrane-bound delivery system

14. Cell Parts
Membrane Organelles
Lysosomes
Membranous sacs that contain powerful enzymes
Help break down foreign material
Peroxisomes
Membranous sacs that contain powerful enzymes
Break down toxic waste products
Produce bile
Detoxify alcohol

15. Cell Parts
Nonmembranous Organelles
Ribosomes
Site of protein synthesis
Can be attached to ER or free floating
Microtubules/Microfilaments
Part of cytoskeleton
Thin, threadlike strands

16. Cell Parts
Nonmembranous Organelles
Cilia/Flagella
Used for cellular movement
Cilia are short and numerous
Flagella are long and usually singular
Centrosomes
Made of microtubules
Help move chromosomes during cell division

17. Cell Parts
Nucleus
Surrounded by a membranous nuclear
envelope (double layer)
Contains the cell’s chromatin (DNA)
The nucleolus is a dense area composed of
newly synthesized ribosomes

18. Cell Parts
Membrane Organelles
Mitochondria
Actually have two membranes (inner and outer)
Site of cellular respiration
Release energy from glucose