Suggestions
Use up and down arrows to review and enter to select.Please wait while we process your payment
If you don't see it, please check your spam folder. Sometimes it can end up there.
If you don't see it, please check your spam folder. Sometimes it can end up there.
Please wait while we process your payment
By signing up you agree to our terms and privacy policy.
Don’t have an account? Subscribe now
Create Your Account
Sign up for your FREE 7-day trial
Already have an account? Log in
Your Email
Choose Your Plan
Individual
Group Discount
Save over 50% with a SparkNotes PLUS Annual Plan!
Purchasing SparkNotes PLUS for a group?
Get Annual Plans at a discount when you buy 2 or more!
Price
$24.99 $18.74 /subscription + tax
Subtotal $37.48 + tax
Save 25% on 2-49 accounts
Save 30% on 50-99 accounts
Want 100 or more? Contact us for a customized plan.
Your Plan
Payment Details
Payment Summary
SparkNotes Plus
You'll be billed after your free trial ends.
7-Day Free Trial
Not Applicable
Renews April 30, 2024 April 23, 2024
Discounts (applied to next billing)
DUE NOW
US $0.00
SNPLUSROCKS20 | 20% Discount
This is not a valid promo code.
Discount Code (one code per order)
SparkNotes PLUS Annual Plan - Group Discount
Qty: 00
SparkNotes Plus subscription is $4.99/month or $24.99/year as selected above. The free trial period is the first 7 days of your subscription. TO CANCEL YOUR SUBSCRIPTION AND AVOID BEING CHARGED, YOU MUST CANCEL BEFORE THE END OF THE FREE TRIAL PERIOD. You may cancel your subscription on your Subscription and Billing page or contact Customer Support at custserv@bn.com. Your subscription will continue automatically once the free trial period is over. Free trial is available to new customers only.
Choose Your Plan
For the next 7 days, you'll have access to awesome PLUS stuff like AP English test prep, No Fear Shakespeare translations and audio, a note-taking tool, personalized dashboard, & much more!
You’ve successfully purchased a group discount. Your group members can use the joining link below to redeem their group membership. You'll also receive an email with the link.
Members will be prompted to log in or create an account to redeem their group membership.
Thanks for creating a SparkNotes account! Continue to start your free trial.
We're sorry, we could not create your account. SparkNotes PLUS is not available in your country. See what countries we’re in.
There was an error creating your account. Please check your payment details and try again.
Please wait while we process your payment
Your PLUS subscription has expired
Please wait while we process your payment
Please wait while we process your payment
When energy sources are high, both glucogenic and ketogenic amino acids are converted to fatty acids through the intermediate acetyl CoA. Other amino acids that are degraded to intermediates in the Krebs Cycle are siphoned off into the production of urea, a nitrogenous carboxyl compound that is filtered through the kidneys and secreted in the urine.
Blood proteins such as albumin and globulin function to maintain fluid balance in the body. When the concentrations of proteins in the bloodstream are low, the fluid in the blood (serum) begins to seep into surrounding tissue. Proteins in the blood can counteract this effect by increasing the osmotic potential and forcing fluid back into the bloodstream. Therefore, low amounts of protein in the blood cause edema, a condition that is characterized by an abnormal amount of fluid in the tissue and extracellular space. Edema is seen in starvation, low calorie diets, and diseases like AIDS that decrease the amount of circulating antibodies and albumin.
Many hormones are composed of polypeptide chains. The beta cells in the pancreas produce the peptide hormone insulin. Insulin facilitates glucose uptake in cells and promotes the synthesis of glycogen and fatty acids. Diabetics must inject the peptide hormone insulin because it will be degraded into amino acids in the stomach and small intestine if taken orally. Other examples of peptide signal molecules include neurotransmitters, a class of molecules that are produced and released at nerve endings in the brain and autonomic nervous system.
Enzymes are an entirely different class of proteins. Enzymes catalyze biological reactions by increasing the reaction rates by factors of at least a million. Since most reactions in the body proceed at imperceptible rates without enzymes, it is critical that these proteins be present in sufficient quantities for proper functioning of cells.
How are enzymes so efficient and fast? First, enzymes are highly specific for their substrates. Substrates are any molecules for which the enzyme binds preferentially or with a high affinity. Enzymes are able to bind specific substrates because they form deep pockets or clefts that are complementary to the three dimensional substrate conformations. Since the enzyme pocket is complementary to the substrate, a large number of noncovalent, dipole-dipole, and Van der Waal interactions can occur, favoring enzyme-substrate binding.
The second reason for the high catalytic rate of enzymes is that they are able to stabilize transition state intermediates. By stabilizing these intermediates, enzymes are able to decrease the activation energy required for the reaction to occur. Upon reaching its high-energy transitional state, the bound substrate can be easily converted to the cell's desired product, which is then released to meet the needs of the cell. These reactions can take place on the order of microseconds to nanoseconds. In fact, many enzymes are so efficient and fast that they approach the diffusion-controlled limit, the rate at which substrate diffusion cannot keep up with the rate at which the enzyme catalyzes the reaction. Enzymes like these have reached catalytic perfection.
Please wait while we process your payment