Chapter 5 – The Working Cell
Objectives:
1. What is energy? Differentiate between kinetic and potential energy.
2. Describe the 1st & 2nd Laws of Thermodynamics.
3. Energy terms to know: entropy, chemical energy, products, reactants, heat, cellular respiration, calorie, &
kilocalories (kcal).
4. What does ATP stand for? What are the three parts of the ATP molecule? Be able to draw the ATP cycle and
label it using the terms phosphorylation, dephosphorylation, endergonic, & exergonic.
5. What is metabolism?
6. What is an enzyme? Define characteristics of enzymes and state their importance to living cells
7. Define the following terms in relation to enzymes:
- Activation Energy
- Catalyst
- Lock and Key theory
- Substrate
- Active site
- Inhibition (2 types)
8. Describe the influence of temperature & pH on the reaction rate
9. Distinguish between the two types of enzyme inhibition.
10. List the components of the plasma membrane and the functions of these components.
11. Differentiate between integral and peripheral proteins
12. Differentiate between diffusion, osmosis, passive transport, facilitated diffusion, & active transport
13. Terms to know with osmosis: hypertonic, hypotonic, isotonic, turgor, flaccid, crenation, & plasmolysis
14. Define endocytosis & exocytosis. Differentiate between pinocytosis, RME, & phagocytosis
I. Basic Energy Concepts
A. Energy makes the world go around – both the cellular world and the larger world outside
1. In order to understand how a cell functions,
B.
1. Energy defined: Energy is the capacity to perform work
a) Work is performed anytime an object is moved against an opposing force
b) In other words, work moves things that would not move on their own
2. Two types of Energy
a)
- The energy of motion
b)
- The energy that an object has because of its location, position, or structure
c) Fig 5.1: Energy Conversions during a dive
3. Energy is neither created nor destroyed but will be converted from one form to another –
a) Ex: A power plant does not make energy, it transforms the energy held in coal, natural gas, etc into
a different form of energy – electricity
C. Entropy
1. Every time that energy is transformed the disorder of the universe (called entropy) increases –
a) Most energy conversions generate heat – a type of kinetic energy contained in the random motion of
atoms and molecules
b) Many man-made systems
- Ex: up to 75% of the energy used by an automobile is lost as heat
- Ex: Traditional incandescent bulbs are also inefficient because they give off so much heat
D. Chemical Energy
1. Molecules in food and fuels possess a special type of potential energy called chemical energy
a) Chemical energy is
b) To harness energy held within these bonds, chemical processes break these bonds to release energy
c) The products of the chemical reactions then have less energy than the beginning molecules
(reactants)
d) In a combustion engine, gasoline mixed with oxygen in an explosive reaction to break down these
fuel molecules in order to propel the vehicle
e) In a cell, the process of cellular respiration converts the energy in organic molecules (like carbs and
fats) to produce an energy form called ATP that the cell can use for work
f) Fig 5.2
2. As mentioned before, energy transfers can be inefficient and
a) Only ~25% of the energy that a car engine extracts from its fuel is used to actually move it
- The rest is lost as heat
- Without a radiator and cooling fans, your cars engine would melt!
b) The process of cellular respiration is slightly more efficient
- About 40% of the energy contained within the food that you eat can be transformed into ATP
for your cells to use
- This heat can be used to maintain homeostasis of body temperature
E. Food Calories
1.
a) It is equal to the amount of energy required to heat one gram of water by 1C
2. Calories are tiny units of measurement, so using them to measure the caloric content of food is not
practical
a) The kilocalorie (kcal) is instead conventionally used
- The nutrition labels on food express the energy content of the food in kcal
b) Fig 5.3 – Caloric Accounting
II. ATP and Cellular Work
A. The energy found within fats, carbs, and other organic molecules cannot be directly used by our cells
1. Instead these organic molecules are broken down through the process of cellular respiration to form
molecules of ATP
a) These ATP
B. ATP structure
1. ATP stands for Adenosine Triphosphate
2.
a) Sugar = Ribose
b) Nitrogen Base = Adenine (Ribose + Adenine = Adenosine)
c) Three phosphate groups ( -PO4)
3. The three phosphate groups are attached to each other to form a phosphate tail
a) Each of the
b) Like charges naturally repel each other, but in this case, energy (a lot) was required to put them
together
c) The 3rd phosphate group is held to the other two
d) Adding phosphate groups is called phosphorylation
- Phosphorylation is called an endergonic reaction because it requires energy to occur
e) Removing phosphate groups is called dephosphorylation
- Dephosphorylation is called an exergonic reaction because it releases energy
- Removing a phosphate from ATP
f) Fig 5.4
4.
a) When the bond between the 3rd & the 2nd phosphate is broken, energy is released and ATP
is changed to ADP
b) ADP can pick up another phosphate and become ATP again
c) Over 10million ATPs are consumed and regenerated per second per cell
d) Draw the ATP cycle – Fig 5.6
5. How does the ATP cycle drive cellular work?
a) The phosphate released during dephosphorylation does not just float off into space
b) ATP energies other molecules in the cell by transferring this energized phosphate group to them
c) Fig 5.5
III. Enzymes
A.
1. The total sum of all chemical reactions in an organism
2. Almost all chemical reactions require the assistance of enzymes
B.
1. Lactase is an enzyme used to break down lactose (milk sugar) into glucose and galactose
2. People who are lactose intolerant do not make enough lactase (or correct lactase) so they cannot digest
(break down) lactose
a) When they consume lactose - they cannot break it down into a form they can use
b) Instead the bacteria in their intestines digest the lactose
c) This causes bloat & gas - aka makes the person sick
d) People that are lactose intolerant can take lactase in a pill form when they are going to consume
lactose or they can avoid/limit lactose (dairy) consumption
C. What are enzymes?
1. Enzymes are:
a) Proteins
- Each enzyme only works on one type of substrate
- A substrate is the molecule that the enzyme reacts with
b) They are catalysts – they speed up the reaction rate by lowering the amount of energy needed for a
reaction to occur
- This energy needed for the reaction to occur
c) They are not used up or changed in the reaction – thus they can be “recycled” and used many times
2. There are so many different types of enzymes and each is very specific to the reaction that it assists
a) The substance that the enzyme is working on is called its substrate
b) Each enzyme has an active site - the site where the enzyme binds with its substrate and transforms it
- This active site is very specific to the substrate that it works on
c) Enzymes being specific to their substrate is
- The Lock & Key Theory was postulated by Emil Fischer in 1894
- In this analogy, the enzyme is the lock and the substrate is the key
- A key (substrate) that is too large, too small, or not the right shape cannot fit with the lock
(enzyme)
d) Draw Enzyme and Substrate:
D.
1. Temperature: Like most chemical reactions, increases in temperature speed up the reaction rate
a) Increases in temp, increase the rate of movement of particles & make it more likely that an enzyme
& substrate will come into contact
b) However, b/c enzymes are proteins, they can exist & function only under a narrow temperature
range
- Above that range,
- When an enzyme is denatured,
c) A decrease in temperature will also decrease the reaction rate
2. pH:
a) Each enzyme has an optimum pH that is functions best in
- Pepsin (enzyme in stomach) optimal pH = 2
- Trypsin (enzyme in small intestine) optimal pH = 8
b) A change in pH changes shape of an enzyme because bonding interactions are changed
E. Control of Enzymatic Activity
1.
a) A form of enzyme inhibition where binding of the inhibitor to the active site of the enzyme
prevents binding of the substrate
b) The enzyme is inhibited by the competitor, so called because it competes with the real
substrate for the active site
c)
d) Example – Sarin gas and many toxins (insectides, pesticides, herbicides, nerve gasses, etc)
work as competitive inhibitors
2.
a) In Feedback Inhibition, there is a second binding site on the enzyme where the inhibitor binds called
the allosteric site
b) The absence or presence of the inhibitor at the allosteric site activates or deactivates the enzyme
c) This type of inhibition often occurs when the products of the reaction build up and there is no need
to keep creating product
d) The inhibition stops the chemical reactions
-Fig 5.10
- You Tube video Feedback Inhibition of Biological Pathways
- You Tube Video ENZYME VIDEO for SJII Biology Class
IV. Membrane Function
A. In addition to controlling the flow of energy and the pace of chemical reactions, cells must also regulate the flow of
materials into and out of the cell
B. Remember the components of the plasma membrane as discussed in Ch 4
1.
a) Phospholipids
b) Cholesterol
c) Carbohydrates
d) Proteins
C. Membrane Lipids
1.
a) Make up the bulk of the membrane
b) Their dual nature is responsible for the hydrophilic and hydrophobic properties of the membrane –
review drawing from Ch 4
2.
a) Maintains the fluidity of the membrane
D.
1. Typically, short, branched chains of sugars on the extracellular side (exterior) of the membrane
2. The membrane plays the key role in cell-cell recognition:
a) To distinguish one type of neighboring cell from another
b) Organization as tissues and organs in development
c) Rejection of foreign cells by the immune system
3. Ex: Human blood groups (A, B, AB, O) reflect differences in the carbs on the RBC’s
E.
1. Proteins lie on top of the plasma membrane or are embedded in it
a) 2 categories of membrane proteins
- 1. Integral proteins: are bound to the hydrophobic interior & extend the entire membrane popping out at either side
- 2. Peripheral proteins: proteins that lie on either side of the membrane but are not bound to
the hydrophobic interior
2. The proteins of the plasma membrane have many functions
a) Membrane Protein Function:
- Certain integral proteins act as channels through material can pass into & out of the cells
- Channels are often hydrophilic passageways through the hydrophobic membrane
- Other proteins act as carrier proteins & actively move materials through the membrane
b) Membrane Protein Function:
- Carry out enzymatic reactions to allow the membrane to function
- Often = the breakdown of ATP to create energy for transport
c) Membrane Protein Function:
- Receptor proteins have binding sites that fit the shape of a specific chemical messenger –
like a hormone
- When a signaling molecule is bound, the shape of the protein may change to relay the
message
- Ex: Insulin is a signaling molecule. When glucose levels are high in the blood, the insulin
binds to receptor proteins. This binding will cause the plasma membrane to change so
d) Membrane Protein Function:
- Some glycoproteins serve as identification tags that are specifically recognized by
membrane proteins of other cells
- Ex: These proteins “tell” our immune system whether a cell is a part of self or a foreign body
e) Membrane Protein Function:
- Membranes proteins of adjacent cells may hook together in various kinds of junctions
f) Membrane Protein Function:
- Elements of the cytoskeleton maybe be covalently bound to membrane proteins
- This maintains cell shape and stabilizes the location of membrane proteins
g) Fig 5.11 Functions of the membrane proteins
V. Movement across the Plasma Membrane
A. Substances do not move across the barrier indiscriminately - membranes are selectively permeable
1. Think of the membrane like a gatekeeper/bouncer – not everything can get across
B. Remember the structure of the phospholipid bilayer
1. The hydrophobic & hydrophilic regions of the membrane affect what can easily cross
a) Non-polar molecules
- “Like will dissolve like”
- Includes: CO2, O2, hydrocarbons, lipids
b) Polar molecules
- Includes: Ions, water, sugars
- These polar molecules are aided by transport proteins
2. Transport proteins can serve as hydrophilic passageway through the membrane
a) Channel proteins: certain ions & polar molecules can use as a “tunnel” through the membrane
b) Carrier proteins: hold on to a specific molecule and
3. We will discuss 3 types of transport across the membrane
a) Passive Transport:
b) Passive Transport: Facilitated Diffusion
c)
C. Passive Transport is diffusion across the membrane
1. Random Movement & Even Distribution
a) When you add a drop of dye to a cup of water, the dye will disperse through the water by itself (you
don’t have to mix it)
b)
- Molecules and ions are in constant motion and the motion is random
- Laws of Thermo Dynamics dictate that because particle motion is random, the particles will
naturally move from an ordered state (dye particles being all together in the drop), to a more
disordered state (dye particles being distributed throughout the water)
2. Diffusion is the tendency of molecules of any substance to spread out in the available space
a) In the absence of other forces, a substance will diffuse from where it is more concentrated to where
it is less concentrated
- This difference in concentration is
b) Fig 5.12
c) YouTube video Diffusion by neuroclip
3. Passive Transport is any movement of molecules or ions across a membrane that does not require the
expenditure of energy
4. Substances that do not spontaneously cross the membrane can be aided by specific transport proteins
a) This type of transport is called Facilitated Diffusion (to facilitate means to assist or help)
- Defined: The passive (no energy needed) movement of molecules down their concentration
gradient via a transport protein –
b) Transport proteins have specific binding sites for the solute
c) You Tube Video Passive Transport by ppornelubio – demonstrates channels
D.
1. Osmosis is the movement of water across a membrane from an area of lower solute [ ] to an area of higher
solute [ ]
a) Another way to think of osmosis: Where is there more free water?
- Water will move from an area w/ more free water to an area with more solutes (less free
water)
b) YouTube video Osmosis by neuroclip
c) Fig 5.13
2. If too much water moves into the cell,
a) Turgor is a force exerted outward on a plant cell wall by the H2O contained in the cell
- This force (called turgor pressure) gives the plant rigidity, and may help to keep it erect
b) Too much turgor may also result in the bursting of an animal cell
3. If too much water leaves the cell,
- When the water leaves the cell, the cell shrivels up
4. Terms with Osmosis: Isotonic Solution
a) In an isotonic solution, the solute [ ] outside of the cell is the same as the solute [ ] in the cell
- There is no net movement of water in or out of the cell
- IV fluids contain .9% salt solution b/c this concentration is isotonic to the blood in humans
5. Terms with Osmosis: Hypotonic Solution
a) The solute [ ] is lower outside of the cell, compared to the solute [ ] inside of the cell
- The cell swells and becomes turgid
- This process is called hemolysis when it occurs in blood cells
- Memory Helper: hypo sounds like hippo - hippos are round
6. Terms with Osmosis: Hypertonic Solution
a) The solute [ ] is greater outside of the cell, compared to the inside of the cell
- The cell shrinks and becomes flaccid
- This process is called crenation in animal cells
- This process is called plasmolysis in plant cells
- Fig 5.15
b) Fig 5.14 - Osmosis in Cells
c) You Tube Video - Osmosis by jerrybraun
E.
1. Active transport is the pumping of solutes against their concentration gradient
a) Movement from an area of low [ ] to an area of high [ ]
b) This is like swimming up stream
c) Without active transport, the [ ] of a substance would always be equal inside of the cell and out
d)
e) It is critical for a cell to maintain its internal concentrations of small molecules
f) Performed by specific proteins embedded in the membranes
g)
h) Fig 5.16
i) You Tube Video - Cell Membrane, Active Transport by neuroclip
VI. Getting the big stuff in & out – Bulk Transport
A.
1. Exo = outside
cyto= cell
a) Removal of substances from the cell through the fusion of a vesicle with the plasma membrane
b) When the two membranes come in contact, the bilayers fuse and spill the contents to the outside
B.
1. Endo = inside
cyto = cell
a) The movement of relatively large materials into the cell by enfolding of the plasma membrane
2. There are three forms of endocytosis
a)
- Pinocytosis literally means cells drinking
- The plasma membrane invaginates to create a kind of harbor
- The harbor then encloses completely and pinches off as a vesicle and moves into the cell’s
cytoplasm
- The vesicle will mostly contain extracellular fluid (usually water) & some solutes
b)
- Receptors bind specific molecules and hold on to them
- The receptors then move laterally through the plasma membrane
- They pinch off into a vesicle
c)
- Phagocytosis literally means “cell eating”
- This is the method that our immune system using to ingest/kill foreign particles
- It is also the way that many single-celled organisms “eat”
- Extensions of the plasma membrane called pseudopods surround the material
- The ends of the psuedopods fuse together forming a vesicle
- The vesicle moves to the cell’s interior
- The lysosomes fuse with the vesicle and begin to break down the material inside of it
C. Fig 5.18
D. Endo & Exocytosis YouTube videoclips
a) Endocytosis by ppornelubio
b) Exocytosis in Paramecium by jsmead
c) Cell Membrane, Exocitosis & Endocitosis by neurocirujo
d) Neutrophil phagocytosis by manuelschutze