Episode 20: Welcome to the MCAT Podcast series, where Doctor Dan will cover the actual science material required for the MCAT. Starting off with an overview of Biological Sciences topics, we’ll get increasingly more specific as time passes.

 

 MCAT Biology 101 [46:31m]: Play Now | Download (2010)

Biology for the MCAT

Classes of Organic Molecules

Four major classes of organic molecules found in living organisms [...]

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Aliases
Solubility
Working Form
Functions
Deficiency
Toxicity

Vit A
Carotene, Retinol
Fat
cis-retinol, trans-retinol, retinoic acid, carotene
Vision, transcription regulation, antioxidant
Vision problems, oxidative damage
Yes (retinol); No (carotene)

Vit B1
Thiamine
Water
TPP
Keto group metabolism
Beri-Beri
No

Vit B2
Riboflavin
Water
FMN, FAD
Electron transfer
Rare
No

Vit B3
Niacin, Nicotinate
Water
NAD+, NADP+
Electron transfer
Pellagra
No

Vit B6
Pyridoxamine
Water
Pyridoxial Phosphate
Transaminase
Rare (isoniazid)
No

Vit B12
Cobalamine
Water
Methyl Cobalamin
Met synth [C1 transfer]; methlmalonyl CoA mutase
Pernicous Anemia
No

Vit C
Ascorbic acid
Water
Same
Antioxidant, hydroxylation of pro & lys
Scurvy
No

Vit D3
Calciferol
Fat
Calcitrol [...]

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Enzymes Subject to Phosphorylation
 
Ca++ and cAMP are intracellular 2nd messengers that respond to hormones binding cell surface receptors
When adenylate cyclase is stimulated, intracellular cAMP levels are elevated (made from ATP)
 
All protein phosphorylation (by kinases) is ATP-dependent and dephosphorylation (by phosphatases) uses H2O and releases Pi
 
 

ENZYME
Substrate, action
Modifying enzymes

Phosphorylated +P

Dephosp “-P”
RESULT

cAMP-dependent [...]

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HYDROLASES:  CLEAVES MOLECULES USING HYDROLYSIS
 
Esterases: a hydrolase that hydrolyzes an ester into its components: an alcohol & an acid.
 
Acetycholine esterase [nerve gas blocks]
Phosphodiesterase 93,104,
Cholesterol esterase 30
 
Lipases: a hydrolase that catalyzes the breakup of ester linkages between a fatty acid & glycerol, w/I triglycerides & phospholipids
 
Serum Lipoprotein Lipase 31
Colipase 30
Gastric Lipase
Pancreatic Lipase [pancreatitis]
Phospholipase A
Lipoprotein lipase 117,118,120, [...]

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Transport Mechanisms
 
Ca++ efflux from ventricular myocardial cells during diastole - secondary active (Na+ coupled)
 
Ca++ uptake by sarcoplasmic reticulum - primary active
 
Ca++ uptake by terminal varicosities of sympathetic nerve endings - restricted diffusion
 
Ca++ entry into heart muscle during plateau phase of the action potential - restricted diffusion
 
Glucose uptake by adipose cell - facilitated diffusion
 
Glucose entry into [...]

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Sickle Cell Anemia (Hb S disease)  - Results when a  glutamate is replaced by  valine at position 6 of the b globin chain.  Symptoms include anoxia, poor circulation, and crises when variables that lower oxygen affinity (i.e. ­BPG, ¯pH, etc) are experienced.
Thalassemia  - Results when either the a- or b- chain is defective.  One type [...]

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Essential Amino Acids
Lys, ISO, LEU, THR, VAL, TRY, PHE, MET, HIS, ARG
Required in diet; no exception
“Little TV Tonight (PM) - HA”
 
Nonessentials
Serine → Gly or Cys (from Homocysteine + Ser)
Glutamate → Gln, Pro, Arg
            -His req. for the syn of Glu
 
One Carbon Metabolism
All begins with Folate; Folate to FH4 via Dihydrofolate reductase (2x)
Formate, His, Ser, Gly, [...]

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