1. Cell Structure & Function
Chapter 4
Cell Structure & Function

2. Cells All living things are made up of cells
Cell: the smallest unit that can carry on all processes of life.

3. Discovery of cells
Microscope observations led to the discovery of the basic characteristics common to all living things
Cells first discovered in the 1600s using crude microscopes
Observations made in the 1800s with the use of more powerful microscopes led to the formation of the cell theory!

4. Cell Theory
3 parts:
All living organisms are composed of 1 or more cells.
Cells are basic units of structure and function in an organism.
Cells only come from the reproduction of existing cells.

5. Cell Theory Led to developments in cell biology
Able to clarify definition of life
All living things share characteristics:
Consist of organized parts
Obtain energy from surroundings
Perform chemical reactions
Change with time
Respond to environment
Reproduce
Maintain homeostasis

6. Cell Diversity Cells vary in A cell’s shape reflects its functions
size
shape
organization
A cell’s shape reflects its functions
The function influences the physical features

7. Cell Diversity Size Reflects different functions of cells
Cells are shaped to perform most efficiently!
A) extensions allow to send and receive nerve impulses
B) platelike allow to cover & protect surface of body

8. Cell Diversity Size Some large enough to be seen by unaided eye
Ex: giraffe nerve cell (from spinal cord to foot) ~2 m.
Human egg cell ~ .
Most cells um
Size is limited by relationship between outer surface area & volume.
Small cells have greater surface area to volume ratio than large cells
Small cells function more efficiently than large cells.

9. Cell Diversity Size Cont’d As cell grows: If a cell became very large:
Volume inc much faster than Surface Area (S.A).
Important because cell needs and wastes must pass through its surface
If a cell became very large:
The volume would increase much larger than S.A.
This S.A. would NOT allow materials to enter or exit cell quick enough for the cell needs
So…Cells are microscopic!

10. Cell Diversity

11. Cell Parts Plasma Membrane Cytoplasm Control Center
Also called Cell Membrane
Cell’s outer boundary
Covers cell surface
Acts as barrier between inside and outside of cell
All materials enter/exit through it
Cytoplasm
Within plasma membrane
Includes fluid, cytoskeleton & all organelles except nucleus
Cytosol- includes molecules & small particles but NOT membrane bound organelles
20% made up of proteins
Control Center
All cells have DNA (coded information)
Some cells DNA floats freely inside
Other cells have nucleus: membrane bound organelle that controls the cell’s function

12. 2 Types of Cells Prokaryotes Eukaryotes Lack membrane bound nucleus
Lack membrane bound organelles
Genetic information stored as DNA
Concentrated in nucleoid
Eukaryotes
Have nucleus
Have membrane bound organelles
Have organelles: intracellular bodies that perform specific functions
Similar to our organ organization
Heart, pancreas, liver all perform functions to enable life

13. Cell Organelles & Features
Plasma membrane
(aka Cell membrane)
Functions:
allows only certain molecules to enter or exit cell
Separates inside from outside
Allows to excrete wastes
Allows interaction with environment

14. The Nucleus Controls most functions of eukaryotic cells (the “brain”)
Filled with liquid nucleoplasm (similar to cytoplasm)
Houses & protects genetic info (DNA)
Contains chromosomes
Nuclear envelope: double membrane that surrounds the nucleus
Nuclear pore: allows RNA & other material to enter/exit through the nuclear envelope
Nucleolus: denser area where DNA is concentrated & ribosome parts are made

15. Mitochondria Aka the “powerhouse” of the cell Function:
Transfer energy from organic molecules to ATP
ATP powers most chemical reactions
Highly active cells (ex: muscle cells) have 100s of mitochondria
Have inner & outer membrane (like nucleus)
Have own DNA
Scientists believe that mitochondria originated from prokaryotic cells that were incorporated with ancient eukaryotic cells.

16. Ribosomes Small spherical organelles made up of protein & RNA
Function:
Build proteins
Ribosome assembly begins in nucleolus & is completed in cytosol
Some float free in cytosol
Others attached to Rough Endoplasmic Reticulum

17. Endoplasmic Reticulum (ER)
A system of tubes & sacs
Function:
Intracellular pathway that allows molecules to move from one part of the cell to another in vesicles
2 Types
1. Rough ER
2. Smooth ER

18. Endoplasmic Reticulum
Rough ER
Covered with ribosomes
Produces phospholipids (ex: digestive enzymes)
Most abundant in cells that produce large amounts of protein (ex: digestive glands, antibody producing cells)
Smooth ER
Lacks ribosomes
Produces lipids (ex: cholesterol or steroids)
Not abundant in cells
Most common in heart, gonads, liver

19. Golgi Apparatus Function: Vesicle is modified as it goes
Receives vesicles from ER that contain newly made lipids or proteins
Vesicle is modified as it goes
Proteins get ‘address labels’ that direct it to other parts of the cell.
Or add carbohydrate ‘labels’ to proteins
Or alter lipids

20. Vesicles
Small spherical sacs with one membrane that migrate to the plasma membrane & release contents outside the cell
Many types of vesicles

21. Vesicles
A) Lysosomes
Bud from golgi apparatus & contain digestive enzymes.
Ex: in liver, lysosomes break down glycogen to release glucose into the bloodstream
Also responsible for autolysis: breaking down cells when time for cell to die
Maintains cell health by destroying cells that are no longer functioning

22. Vesicles B) Peroxisomes
Similar to lysosomes but contain different enzymes & aren’t produce by the golgi apparatus.
Function: neutralize toxins & free radicals found in liver & kidney
Named for H2O2 produced from breaking down alcohol
Also break down fatty acids for mitochondria to use

23. Protein Synthesis
Step 1: Proteins assembled by ribosomes on the rough ER
2: Vesicles transport proteins to the Golgi apparatus
3: Golgi modifies proteins and packages them in new vesicles
4: Vesicles release proteins that have destinations outside the cell
5: vesicles containing enzymes remain inside the cell

24. Cytoskeleton 3 components:
Thin tubes & filaments that crisscrosses the cytosol
Similar to tent poles supporting the tent
Function:
Support & Transport
3 components:
Microtubules
Microfilaments
Intermediate Filaments

25. Cytoskeleton: 3 components

26. Cilia & Flagella
Hairlike structures that extend from surface of the cell
Function:
Assist in movement
Cilia: short & many present
Ex: inner ear cilia help detect sound
Flagella: long & few present
Ex: human sperm cells

27. Centrioles Occur in animal cells Plants lack centrioles Function:
Organize microtubules during cell division

28. Plant Cells Contain organelles & parts common to eukaryotic cells
Also have 3 addition structures:
Cell Wall
Large central vacuole
Plastids
Why?
different lifestyle than animal cells
Make own food
Perform photosynthesis

29. Cell Wall Rigid layer outside plasma membrane
Contains cellulose (a carbohydrate)
Forms stiff box around each cells
Pores in cell wall allow water, ions & some molecules to enter/exit cell
There are primary & secondary cell walls.
All plants have primary. Some have secondary.
Ex: wood desks & tabletops

30. Central Vacuole Function: Can make up 90% of cell’s volume!
Store large amounts of water, enzymes, wastes, & other materials
Can make up 90% of cell’s volume!
When a plant is watered, the vacuole fills, cells expand, and the plant stands up straight.
Other vacuoles store toxins & pigments

31. Plastids
Organelles similar to mitochondria (have double membrane & own DNA)
Several types:
Chloroplasts
Chromoplasts
Other plastids
All arose from protoplastids

32. Plastids Chloroplasts: use energy to make carbohydrates from CO2 & H2O
Contain thylakoids: flattened sacs that contain chlorophyll
Chlorophyll: molecules that absorb light & captures light energy
Have own DNA:
Scientists believe that chloroplasts originated from prokaryotic cells that were incorporated with ancient eukaryotic cells.
Chromoplasts: contain colorful pigments

33. Comparing Cells All cells share 4 common features:
Cell membrane
Cytoplasm
Ribosomes
Genetic Material
3 Main types of Cells
Prokaryotic
Eukaryotic
Differences among eukaryotic
Plant vs. Animal Cell

34. Prokaryote vs. Eukaryote Cells
Prokaryotes: lack nucleus, have nucleoid, lack membrane bound organelles, lack internal membrane system

35. Plant vs. Animal Cells
Plants: have cell wall, large central vacuole & plastids