Cell Membrane

GENERAL BIOLOGY LECTURE | ST. CHARLES COMMUNITY COLLEGE

Chapter 5: The Working Cell

The nature and laws of energy, the metabolic pathways and energy transformations in cells, the role of enzymes in metabolism, oxidation-reduction reactions, and production and use of ATP in cells are discussed in this chapter.

The complex structures and functions of the plasma membrane are introduced. The general methods used to move molecules get in and out of cells are described. Important cell surface modifications are also detailed.

Membranes not only surround the cell (e.g. the plasma membrane), but they also extend throughout the cytoplasm and form the structure of many cellular organelles including the membranes chloroplasts, mitochondria, central vacuoles, vesicles, golgi bodies, and endoplasmic reticulum. For chemicals to get into or out of the various organelles within a cell they must pass across a membrane and membranes to a large extent control what chemicals go in and what chemicals go out of the organelles.

SOME BASIC ENERGY CONCEPTS

Please read and ponder: Ultimately that outside energy source is the Sun (you've heard that before, yawn). The sun’s energy is channeled through plants into chemical bonds (maybe there's something new to learn here). The chemical bonds store energy that was once light energy. Chemical bonds are the basis of food energy. Plants make food from nonfood (i.e. CO₂) using energy of light. All animal life and all decomposers depend directly or indirectly on energy in food made by plants. Plants constantly convert light energy into food energy thus supplying the living world its energy needs. Without the action of plants converting light energy into food energy (via photosynthesis) the living world wood soon run out of useable energy and life would cease. We convert some of the energy of plants into our own bodily energy stores. Unlike aluminum cans, this food energy can’t be recycled indefinitely because each time we convert energy from its source (food) some is “lost” as heat (random molecular motion)—randomness is in contrast to the highly ordered structure of living organisms. If the world were a closed system, it would soon run out of useful energy and life would end. The Sun of course provides the energy life needs. Light energy from the sun simply needs converting into the chemical energy of organic molecules (the process generally called PHOTOSYNTHESIS). The primary carbohydrate energy molecules synthesized during photosynthesis are starting molecules for further chemical reactions such as conversion of carbohydrate energy into the energy required to assemble amino acids during protein construction. Energy conversions by living beings are accomplished via metabolism, and metabolism is accomplished by chemical reactions. More to come.

Energy makes the world go round: What is energy?

I. Conservation of Energy

Energy is defined as ______________________________________________.

A rather uninspiring definition, & we should acknowledge that the concept of energy is difficult to fully grasp. Energy is intangible, takes up no space, has no mass, it is not material, not hard and concrete. Perhaps if we consider two states of energy we can further develop the concept of energy.

1) Kinetic Energy - energy of motion, "energy in progress or action"

2) Potential Energy - stored energy. A rock on a ledge has stored energy. If the rock is pushed off the ledge it will release this stored energy as it falls through the air. The energy released performs work, i.e., stirs the air or crushes objects in its path. Chemical bonds also store potential energy. Like taut rubber bands holding atoms together, when broken chemical bonds release energy and perform work, e.g. a muscle contracts, new chemicals are assembled.

Energy can be changed from ______________________________________. However, it can not be ___________________ or ______________. This is the ______________________________________.

II. Entropy

Heat:

Is a type of ______________________. Is a product of ____________________________________.

Scientists use the term entropy as a measure of ___________________________ or _______________________________.

All energy conversions increase the entropy of the _________________________________.

II. Chemical Energy

Chemical energy is:

1. _______________________________________

2. _______________________________________

Cellular respiration:

1. _______________________________________

2. _______________________________________

III. Food Calories

A _______________ is the amount of energy that raises the temperature of one gram of water by one degree Celsius.

The kilocalorie is:

1. __________________________

2. __________________________

The _____________________ of calories in food is burned off by many activities.

Basal metabolic calculator: http://bodybuilding.com/fun/calrmr.htm

ATP AND CELLULAR WORK

The chemical energy of ______________________________ is released in ______________________ to make _________ in the mitochondria.

I. The Structure of ATP

ATP:

1. __________________________________________

2. __________________________________________

II. Phosphate Transfer

ATP can energize other molecules by transferring ___________________________. This energy can be used to drive ______________ work.

III. The ATP Cycle

Cellular work spends _______________. ATP is recycled from _____________ and _______________ through cellular respiration.

ATP functions in what is called ____________________________ or the _____________________.

ATP – the energy currency of the cell; ATP needed for many enzyme catalyzed reactions.

ATP stores energy when ATP is formed and ATP releases energy when ATP is broken down. The stored ATP energy comes from the food we breakdown during cellular respiration. The released ATP energy provides the quantity of energy needed for reactions that require energy input, ex. muscle contractions & building new molecules for cell growth (neither process can use food energy directly, the energy of food must first be transferred to ATP during ATP synthesis). Keep in mind that some of the food we eat is not for energy needs, but rather for materials to build our bodies--“you are what you eat”---at least that’s where your material body comes from, a restructuring of the food molecules ingested. The energy from food combusted to CO₂ through cellular respiration yields the energy in the form of ATP needed to perform this molecular reconstruction of food molecules into the molecules of your body. Thus “food,” a non-technical term, has two purposes: 1) some food is destroyed as its chemical bond energy is transferred to ATP (waste CO₂ is released in the process); 2) some food is molecularly rearranged keeping its organic structure but forming your body.

ENZYMES

________________________ is the sum total of all chemical reactions that occur in organisms. Few metabolic reactions occur without the assistance of ____________________________.

Biochemical pathway animation: http://www.stolaf.edu/people/giannini/flashanimat/enzymes/biochem.path.swf

I. Activation Energy

Activation energy:

1. _____________________________________

2. _____________________________________

Enzymes lower the _____________________________ for chemical reactions.

II. Induced Fit

Each enzyme is very _______________________. It __________________ specific reactions.

Each enzyme recognizes a specific ___________________. The _________________ fits to the substrate, and the enzyme changes _________ slightly. This interaction is called ___________________.

Enzymes can function ______________________________.

III. Enzyme Inhibitors

Enzyme inhibitors:

1. _________________________________

2. _________________________________

Other inhibitors:

1. _________________________________

2. _________________________________

What is an enzyme? http://programs.northlandcollege.edu/biology/Biology1111/animations/enzyme.html

Enzyme activity: http://www.lewport.wnyric.org/jwanamaker/animations/Enzyme activity.html

Enzyme reaction simulation: http://www.bbc.co.uk/education/asguru/biology/02biologicalmolecules/01proteins/11enzymes/03enzymes_b/index.shtml

How Heat Changes Protein Structure: http://www.sumanasinc.com/webcontent/anisamples/nonmajorsbiology/proteinstructure.html

Allosteric animation: http://www.stolaf.edu/people/giannini/flashanimat/enzymes/allosteric.swf

Biochemical pathways and Feedback inhibition: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html#

MEMBRANE FUNCTION

Working cells must control the flow of materials _____________________________________________. Membrane _____________ help with this task. Membrane proteins perform a variety of functions:

1. ___________________________

2. ___________________________

3. ___________________________

4. ___________________________

5. ___________________________

6. ___________________________

Fluid MosaicModel. http://cellbio.utmb.edu/cellbio/membrane.htm

Cell Membrane structure: http://home.earthlink.net/~shalpine/anim/Life/memb.htm and http://www.bio.davidson.edu/people/macampbell/111/memb-swf/membranes.swf

Dynamic cell membrane: http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf

Phospholipids are arranged in a bilayer. http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/orient2.swf

I. Passive Transport: Diffusion Across Membranes

Molecules contain __________________. They ___________ and ______________ randomly.

_______________ is one result of the movement of molecules. Molecules tend to _____________________________________.

Diffusion is ________________________: no energy is needed.

ex. CO₂, O₂, alcohol & H₂O all readily diffuse across membrane surfaces; The importance of this is that cells are in some sense powerless to control the movements of these molecules; they will move along their concentration gradient, i.e., from high to low conc. If O₂ is more highly concentrated outside of cell then it will move into the cell by simple diffusion. Concerning alcohol, your cells “don’t know when to say when.”

Another type of passive transport is _________________________ , the transport of some substances by specific transport proteins that act as selective _____________________.

II. Osmosis and Water Balance in Cells

Osmosis is passive transport of _____________ across a selectively permeable membrane.

A hypertonic solution: _________________________________

A hypotonic solution: __________________________________

An isotonic solution: __________________________________

A. Water Balance in Animal Cells

The survival of a cell depends on its ability to balance _______________ uptake and loss.

Plasymolysis: ___________________________________________.

__________________________ is the control of water balance in animals.

Salt excretion: body fluids of most marine fish are hypotonic to sea water, to maintain this homeostasis, these fish drink sea water and excrete the salt and retain the water.

Kidneys – removes any excess water from body fluids. (the kidney also removes waste chemicals such as urea for elimination from the body). Freshwater fish are hypertonic to lake water and thus their cells will swell and burst if their kidneys weren’t so good at constantly removing excess water (so freshwater fish pee a lot and drink very little).

Cell wall of plants and fungi – Plants don’t have a kidney, but their design keeps them from swelling and bursting thanks to a bounding cell wall that maintains turgor pressure under normal, well watered conditions.

B. Water Balance in Plant Cells

Water balance in plant cells is different:

1. ___________________________________

2. ___________________________________

Click on http://edtech.clas.pdx.edu/osmosis_tutorial/diffusion1.html for diffusion and osmosis animation.

Membrane Transport: http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

Diffusion, Dialysis and Osmosis tutorial: http://science.nhmccd.edu/biol/osotutor.html

Diffusion and osmosis virtual lab: http://www.phschool.com/science/biology_place/labbench/lab1/intro.html

Non interactive site on diffusion and osmosis...good illustrations: http://www.biologycorner.com/bio1/diffusion.html

III. Active Transport: The Pumping of Molecules Across Membranes

Active transport requires ________________ to move molecules across a membrane.

In active transport, molecules are moved into or out of cell against their concentration gradient, i.e. from low to high concentration and therefore this is opposite of diffusion, is not spontaneous, and requires cellular energy [ATP]. Active transport occurs where membrane proteins act as pumps, pumping Na⁺, K⁺, Cl^-, ions pumped across nerve cell membranes that maintains an electrical potential. These ions are the so-called electrolytes.

IV. Exocytosis and Endocytosis: Traffic of Large Molecules

_____________________ secretes substances outside the cell.

_____________________ takes material into the cell.

In ______________________ ("cellular eating"), a cell engulfs a particle and packages it within a food vacuole.

In ______________________ ("cellular drinking"), the cell "gulps" droplets of fluid by forming tiny vesicles.

___________________________ is triggered by the binding of external molecules to membrane proteins.

V. The Role of Membranes in Cell Signaling

Cellular communication begins with _______________________________________.

The ________________________________ consists of proteins and other molecules that relay the signal.

EVOLUTION CONNECTION: EVOLVING ENZYMES

Organism use many different ____________________. How could this diversity arise:

1. _______________________________________

A lab procedure called ____________________________ , in which genes for a particular enzyme were mutated at random.

Produced new enzymes that recognized new ____________________.

.

Cell Transport animation: http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm

Animations on Active transport: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html

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