Month: September 2020

To understand the basic energy rules, view the slideshow

Energy Rules

Here is a video on thermodynamics and perpetual motion machines

Perpetual Motion machines and Thermodynamics

Enzymes:  First watch this video

Amoeba sisters Enzyme video with embedded questions

Know what substrates are and how they relate to enzyme catalyzed reactions.

Example what is the substrate in this enzyme catalyzed reaction

Lactose→Glucose + Galactose?

The enzyme in this reaction is lactase

Know how enzymes catalyze biological reactions, specifically their effects on activation energy. 

Another concept in how enzymes speed up reactions is activation energy. Imagine you have a homework assignment due next week. You could do it now, or you could put it off until right before it is due.  The activation energy is the energy needed to get the process started. Note that the homework might take you an hour whether you do it now or later. The activation  energy is just what it takes to get started. Enzymes decrease activation energy as shown in the diagram in the link

Activation Energy

 

Note that that the ΔG (The overall energy) does not change whether or not the enzyme is present. Enzymes also have no effect on the equilibrium of a reaction; adding an enzyme does not shift the reaction to the left or right.  It does change how quickly the reaction reaches equilibrium.

A property of enzymes is that they become saturated at high enough substrate concentrations. You will explore that in this week’s lab.

(see link in this week’s reading. For some reason the link is not working from this site.)

Many drugs can inhibit enzyme function by binding to the active site. Here is an example

HIV Drug Action

The key point here is that the inhibitor binds very strongly to the active site preventing the substrate from binding. Because both the inhibitor and substrate bind to the same site, the binding is said to be competitive.  If the concentration of substrate increases, the inhibitor is less effective.

We have already mentioned active sites, they bind to the substrate(s) of a reaction. Some enzymes also have allosteric sites. These do not bind to substrates but they bind to compounds that can turn on (activators) or turn off (inhibitors) an enzyme as shown in this video

Allosteric regulation of enzymes

Non-competitive inhibitors bind to the allosteric site.  Adding more substrate has no effect on allosteric inhibitors since the inhibitor changes the active site to be “closed”.

Know what feedback inhibition is and how it can be used to control amino acid synthesis.

Feedback inhibition

Here is an example of how this works to control amino acid levels

Feedback inhibition o f amino acid synthesis

 

 

 

 

 

Membranes

Review of Lipid and Membrane structure

Phospholipid structure

 

the above structure is a phospholipid. Note the polar head (top) and hydrophobic tails (bottom). One of the tails is bent due a a double bond.

Lipids arrange themselves in bilayers as described here

Lipid Bilayer

Note the round heads oriented toward the outside (water) and the tails oriented toward each other (inside of membrane). This limits transport of many types of molecules (See below)

Membrane Structure

 

This image shows the lipid bilayer along with proteins carbohydrates

Functions for membrane proteins

Transport of substances across membranes: the following types of substances can be transported across lipid bilayers without the help of proteins

(1) Non-polar compounds including gases such as oxygen and carbon dioxide and larger compounds such as steroids

(2) Water and some very small polar compounds. Water travels slowly

Reception. Membrane proteins help detect internal signals (such as insulin) and external signals (such as sugar, for taste buds). Binding of the compound on the outside triggers a series of reactions that leads to a response.

Recognition For example self vs nonself immune reactions are determined by membrane proteins and or carbohydrates. The difference between blood types A,B AB and O is determined by  different carbohydrates.

Formation of organs like liver and stomach can depend on membrane proteins sticking like cells together.

Junction formation Gap, Tight and Adhesion junctions are made of membrane proteins

Role of cholesterol

In cold temperatures, cholesterol breaks up phospholipid packing (in a manner similar to unsaturated fats. This makes the membranes more fluid)

At high temperature, cholesterol limits the lateral movement of phospholipids, thus making the membrane less fluid.

Be able determine whether an environment is hypotonic, isotonic or hypertonic to a cell.

Be able to predict what will happen if a plant or animal cell is put in a hypotonic, isotonic or hypertonic environment.  .

Example:

• A cell with an internal NaCl concentration of . 1M is put into a solution of ..05 M NaCl. The salt can not cross the membrane. What happens?

This video covers  membrane transport including endo and exocytosis

Crash Course, Membranes and Transport

Here is a video (also linked in the open stax text showing how receptor mediated endocytosis regulates cholesterol level

LDL function

 

exocytosis review

Test Your Self on Membrane transport