Cells Part 2: Cell Structures

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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?

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

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)

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

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

Complete Simple Diagram

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

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

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

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

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

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

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

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

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

ATP Synthase

Cellular Respiration Summary

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