1. Cells Part 2: Cell Structures

2. By the end of this class you should understand:
The major organelles common to all human cells
The nature of exceptions to the general rules of organelles
The concept of energy use to maintain homeostasis
The major molecules used for cellular energy
The complete three-step process of ATP production

3. Important Note:
Organelles are important parts of all cells in the human body
Special exceptions noted
These parts keep the cell alive
All human cells also contribute additional functions to the overall body
Muscle cells have fibers that contract
Glands secrete hormones
Bone cells produce bone matrix
Etc etc etc

4. Parts of the Cell (organelles)
Nucleus
Cell membrane
Cytoskeleton
Cytoplasm
Mitochondria
Ribosome
Endoplasmic Reticulum
Golgi Apparatus

5. Nucleus: The Library
The nucleus stores all the cell's genetic information in massive molecules of DNA
The DNA molecules are packed into many pairs of chromosomes
When a protein is needed, signals enter the nucleus and cause copies of the appropriate genes to be made with RNA

6. Key Nucleus Facts: Every complete human cell has one nucleus
Exception: red blood cells have no nucleus (also have no other membrane-bound organelles)
Exception: muscle cells are many cell fused together and so have many nuclei
Every nucleus has the complete human genome
The nucleus has its own envelope to keep unwanted things out

7. Cytoskeleton: The City Streets
Every cell has long strands of different kinds of proteins running through it
When organelles are moved they move along the cytoskeleton
If the cell moves under its own power it uses the cytoskeleton as well

8. Key Cytoskeleton Facts:
There are several different types of fibers and they have different functions
All cells must produce each of these fibers
These fibers are made of different kinds of proteins (keratin, collagen, actin, myosin, etc)
If the genes for any of these fibers are no good, no cells can form and the organism will never develop, grow or be born
This makes these genes essential for life

9. Cytoplasm: The Marketplace
The liquid of the cell is called cytosol
Cytosol plus the organelles are called cytoplasm
All the cell's chemical reactions and growth take place here
Many exchanges are made
Many chemicals are stored in vesicles in the cytoplasm

10. Key Cytoplasm Facts:
Cytosol is a clear liquid but it is filled with salts and sugars
Cytoplasm is held within the cell membrane
If the cell membrane develops a hole, cytoplasm can leak out and the cell can die
If the cell membrane bursts all at once, this is called lysis and is instant cell death

11. Ribosome: The Machine Shop
Site of protein synthesis
Some are free floating in cytoplasm
Some are attached to membranes called the endoplasmic reticulum
Made with a combination of protein and RNA
Probably the first structure in the original cells

12. Key Ribosome Facts Ribosome is the site for proteins to be synthesized
That process will be discussed next week
Cytoplasmic ribosomes make the cytoskeleton and cell enzymes
Rough endoplasmic reticulum produces proteins that will enter the membrane or leave the cell
Smooth endoplasmic reticulum is for synthesis of other macromolecules such as lipids

13. Golgi Apparatus: The Shipping Center
Vesicles from the endoplasmic reticulum are organized here
Different vesicles have different destinations
The chemical reactions that determine where these vesicles go occur here

14. Key Golgi Facts
The Golgi manipulates cell membrane material into many types of vesicles
Peroxisomes contain peroxides
Lysosomes contain destructive enzymes (that can lyse chemicals or even other cells)
Secretory vesicles are designed for exocytosis (they will secrete their contents)

15. Mitochondria: The Power Plant
Mitochondria (singular: mitochondrion) produce the cell's supply of energy molecules
Cells use a molecule called ATP
Made using the energy from blood sugar
Must have oxygen to work
Process that requires oxygen is called aerobic

16. Key Mitochondria Facts:
Mitochondria were once bacteria
Captured/adopted by animal cells billions of years ago and now we work together
Mitochondria must have oxygen to burn sugar
Produce CO2 as a waste product
This is why we breathe in oxygen and breathe out carbon dioxide
Mitochondria sustain our high metabolic rate
Cyanide blocks mitochondrial activity, which is why it is a lethal poison to us

17. Cellular Homeostasis Every cell must perform the following tasks:
Take in materials
Build proteins
Excrete wastes
All these processes require energy!
Chemical energy is delivered in the form of ATP

18. ATP Primary energy molecule Starts as an adenosine with two phosphates
Gets “charged up” by having a third phosphate added to the tail
Can “release” that energy for other chemical reactions
Third phosphate bond is high-energy but unstable
Compare to C-C bond which is also high energy but very stable and can be stored

19. Other uses of ATP: Used to make muscles contract
Kidney reabsorbs nutrients from urine
Neuron ion pumps to make electrical signals
Absorb nutrients from small intestine
Make new cells (mitosis/meiosis)
Basically everything you do

20. What is needed to make ATP?
ADP (nucleic acid) and phosphate
There is plenty of this in the cell already since it gets reused a lot
Energy source (carbohydrate, protein, lipid)
Oxygen (for aerobic respiration only)
How do these reach the cells?

21. How do these get to cells?
Blood!
Glucose is the sugar dissolved in our blood
Oxygen is carried by red blood cells
Nucleic acids and amino acids are also carried in the blood to cells
Fat is moved via lipoproteins (LDLs move fat to cells, HDLs move fat to liver) via bloodstream
Heart failure = death because your cells starve

22. Which cells do this? All cells need energy
All cells with mitochondria perform complete cellular respiration
Cells with no mitochondria or nucleus (i.e. Red Blood Cells) can only perform anaerobic respiration (glycolysis)

23. Complete Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + ATP

24. Technically a Combustion Reaction:
C6H12O6 + 6O2  6CO2 + 6H2O + Heat

25. Complete Simple Diagram

26. Cellular Respiration Three steps to complete cellular respiration:
Glycolysis
Krebs Cycle (citric acid cycle)
Electron Transport Chain
“Lysis” = “breaking”
Glycolysis: breaking in half of glucose
Produces some energy
Krebs Cycle + ETC are aerobic
Only work when oxygen is present

27. Glycolysis Enzyme-catalyzed Anaerobic Has 10 steps
What your muscles use when you are exerting yourself more than you can breathe
Has 10 steps
We will NOT be going over this
Reactant: 1 glucose (6-carbon)
Product: 2 pyruvate (3-carbon) and 2ATP

28. Glycolysis Performed in the cytoplasm
Occurs automatically when glucose is brought into the cell
Fructose and galactose can also be broken with glycolysis

29. Fermentation
If no oxygen is present, pyruvate buildup in cell can become toxic
Pyruvate is instead converted to lactic acid
Lactic acid enters bloodstream and creates the “burning” feeling in your muscles

30. Krebs Cycle The Krebs Cycle is an enzymatic process
Aerobic: requires oxygen to keep running
If no oxygen, no electron carriers available
Reactant: 1 Acetyl CoA
Pyruvate is converted to Acetyl CoA
Product: 3 CO2

31. Krebs Cycle Performed in the mitochondria
Produces ATP and high-energy electrons
Produces the CO2 that we breathe out
CO2 exits cell and dissolves into blood until we breathe it out at the lungs

32. Electron Transport Chain
Electrons are pushed one by one through a transport chain
As the electron moves, its energy is used to pump hydrogen ions into a special reservoir
Sort of like using energy to pump water to a lake above a dam
As the hydrogen ions are released back, they turn a “water wheel” that makes ATP

33. Electron Transport Chain
Each of these structures pulls a little more tightly on the electron
The final recipient of the electron is oxygen, which makes water
This means the entire chain is aerobic

34. Electron Transport Chain
The energy in the electron does work to create a gradient of hydrogen ions
The hydrogen ions move down their gradient through an ATP Synthase enzyme
This enzyme creates ATP when turned by hydrogen ions
This is called chemiosmosis
This step makes a LOT of ATP

35. ATP Synthase

36. Cellular Respiration Summary

37. Cellular Respiration Summary:
Glucose
is broken down by glycolysis to
Pyruvate
which enters the Krebs cycle and becomes
CO2
which leaves, but the released electrons power the
Electron Transport Chain
which makes fat stacks of ATP
oxygen absorbs the electrons to become water