set 2: biology and biochemistry MCAT review

cardiovascular system consists of what

a muscular four chambered heart, blood vessels, and blood

the heart is composed of

two types of circulation

cardiac muscle and supports two diff circulations: the pulmonary and systemic circulation

each side of the heart contains a

atrium and ventricle

atria are separated from the ventricles by (names for right and left)

the atrioventricular valves

tricuspid on the right and bicuspid (mitral) on the left

ventricles are separated from the vasculature by the (right/left names)

semilunar valves

pulmonary on right, aortic on the left

pathway of blood

right atrium→tricuspid valve→right ventricle→pulmonary valve→pulmonary artery→lungs→pulmonary veins→left atrium→mitral valve→left ventricle→aortic valve→aorta→arterioles→capillaries→venules→veins→venae cavae→right atrium

which side of the heart has more muscle

left side bc the systemic circulation has a much higher resistance and pressure

electrical conduction pathway

starts at the sinoatrial (SA) node and then goes to the atrioventricular (AV) node

from the AV node, electrical impulses travel to the bundle of His before traveling through the purkinje fibers

systole

refers to the period during ventricular contraction when the AV valves are close

diastole

the heart is relaxed and the semilunar valves are closed

cardiac output (eq)

is the product of heart rate and stroke volume

CO= HR * SV

sympathetic nervous system vs parasympathetic ns affect on HR

s: inc HR

p: dec HR

vasculature consists of what three items

arteries, veins, and capillaries

arteries and arterioles

thick, highly muscular structures with an elastic quality

this allows for recoil and helps to propel blood forward within the system

small muscular arteries are arterioles, which control flow into capillary beds

capillaries

have walls that are one cell thick, making them so narrow that red blood cells must travel through them single file

are the site of gas and solute exchange

veins and venules

how do they maintain one way flow?

are inelastic, thin walled structures that transport blood to the heart

they are able to stretch in order to accomodate large volumes of blood but do not have recoil capability

veins are compressed by surrounding skeletal muscles and have valves to maintain one way flow

small veins are called venules

a portal system

is one in which blood passes through two capillary beds in series

hepatic portal system

blood travels from the gut capillary beds to the liver capillary bed via the hepatic portal vein

hypophyseal portal system

blood travels from the capillary bed in the hypothalamus to the capillary bed in the anterior pituitary

the renal portal system

blood travels from the glomerulus to the vasa recta through an efferent arteriole

blood is composed of

cells and plasma, an aqueous mixture of nutrients, salts, respiratory gases, hormones, and blood proteins

erythrocytes (red blood cells)

common measurements of RBC

lack mitochondria, a nucleus, and organelles in order to make room for hemoglobin, a protein that carries O2

common measurements include hemoglobin conc and hematocrit, the percentage of blood composed of erythrocytes

leukocytes (white blood cells)

are formed in the bone marrow

they are a crucial part of the immune system

granular leukocytes vs agranulocytes

g: such as neutrophils, eosinophils, and basophils play a role in nonspecific immunity

a: including lymphocytes and monocytes also play a role in immunity, with lymphocytes playing a large role in specific immunity

thrombocytes (platelets)

are cell fragments from megakaryocytes that are required for coagulation

blood antigens (surface antigens and Rh factor)

-allele patterns and antibodies

surface antigens A, B, and O

and Rh factor D

the I^A (A) and I^B (B) alleles are codominant, while the i (O) allele is recessive

people have antibodies for any AB alleles they do not have

pos Rh factor is dominant

an Rh-neg individual will only create anti-Rh antibodies after exposure to Rh-pos blood

blood pressure

refers to the force per unit area that is exerted on the walls of blood vessels by blood

it is divided into systolic and diastolic components

it might be high enough to overcome the resistance created by arterioles and capillaries, but low enough to avoid damaging the vasculature and surrounding structures

how is BP measured

sphygmomanometer

how is BP maintained:

low BP

high blood osmolarity

high BP

maintained by baroreceptor and chemoreceptor reflexes

low BP promotes aldosterone and antidiuretic hormone (ADH or vasopressin) release

high blood osmolarity also promotes ADH release

high blood pressure promotes atrial natriuretic peptide (ANP) release

gas and solute exchange at capillaries

occurs at the level of the capillaries and relies on the existence of concentration gradients to facilitate diffusion across the capillary walls

capillaries are also leaky, which aids in the transport of gases and solutes

starling forces (hydrostatic vs osmotic/oncotic pressure)

consist of hydrostatic pressure and osmotic (oncotic) pressure

hydrostatic pressure is the pressure of the fluid within the blood vessel, while osmotic pressure is the “sucking” pressure drawing water toward solutes

oncotic pressure is osmotic pressure due to proteins

hydrostatic pressure forces fluid out of the arteriolar end of a capillary bed; oncotic pressure draws in back in at the venule end

cooperative binding—in lungs vs in tissues and general pattern of affinity

O2 is carried by hemoglobin, which exhibits cooperative binding

in the lungs, there is a high partial pressure of O2, resulting in loading of O2 onto hemoglobin

in the tissues, there is a low partial pressure of O2, resulting in unloading

with cooperative binding, each successive O2 bound to hemoglobin inc the affinity of other subunits, while each successive O2 released dec the affinity of the other subnets

CO2’s diff forms and nature in blood

CO2 is largely carried in the blood in the form of carbonic acid, or bicarbonate and hydrogen ions

CO2 is nonpolar and not particularly soluble, while bicarbonate, hydrogen ions, and carbonic acid are polar and highly soluble

oxyhemoglobin dissociation curve

what causes shifts to the right or left and what does this shift mean in terms of O2 affinity

a high PaCO2, high [H+], low pH, high temp, and high conc of 2,3-BPG can cause a right shift in the oxyhemoglobin dissociation curve, reflecting a dec in affinity for O2

in addition to the opposites of the causes of a right shift, a left shift can also be seen in the dissociation curve for fetal hemoglobin compared to adult hemoglobin

nutrients, wastes, and hormones are carried in the bloodstream to

to tissues for use or disposal

coagulation and coagulation cascade

results from an activation cascade

when the endothelial lining of a blood vessel is damaged, the collagen and tissue factor underlying the endothelial cells is exposed

this results in a cascade of events known as the coagulation cascade, ultimately resulting in the formation of a clot over the damaged area

platelets bind to the___and are stabilized by___, which is activated by ___

bind to the collagen and are stabilized by fibrin, which is activated by thrombin

plasmin

clots can be broken down by plasmin

ohm’s law applied to circulation eq.

delta P = CO * TPR

pressure differential across the circulation = cardiac output times total peripheral (vascular) resistance

central dogma

states that DNA is transcribed to RNA, which is translated to a protein

a generate code allows for what property of codons

allows multiple codons to encode for the same AA

start codon

stop codons (3)

AUG

UAA, UGA, UAG

redundancy and wobble allows for what properties of codons

wobble (third base in the codon)

allows for mutations to occur without effects in the protein

point mutations can cause (3 mutation types)

silent—with no effect on protein synthesis

nonsense (transaction)—mutations that produce a premature stop codon

missense—that produce a codon that codes for a diff AA

frameshift mutations

result from nucleotide addition or deletion and change the reading frame of subsequent codons

RNA structure is similar to DNA except: (3)

substitution of a ribose sugar for deoxyribose

susitution of uracil for thymine

it is single stranded instead of double stranded

three types of RNA with their separate jobs in transcription (mRNA, tRNA, rRNA)

messenger RNA—carries the message from DNA in the nucleus via transcription of the gene; it travels into the cytoplasm to be translated

transfer RNA—brings in AA and recognizes the codon on the mRNA using its anticodon

ribosomal RNA—makes up the ribosome and is enzymatically active

helicase

unwinds DNA double helix

RNA polymerase I

binds to the TATA box within the promoter region of the gene (25 base pairs upstream from first transcribed base)

hnRNA

is synthesized from the DNA template (antisense) strand

post transcriptional modifications include: (4—one is how prok vs euk cells inc variability)

a 7-methylguanylate triphosphate cap added to the 5’ end

a poly adenosyl (poly-A) tain is added to the 3’ end

splicing done by snRNA and snRNPs in the spliceosome; introns are removed in a lariat structure, and exons are ligated together

prok cells can inc the variability of gene products from one transcript through polycistronic genes (in which starting transcription in diff sites within the gene leads to diff gene products)

euk cells can inc variability of products through alternative splicing (combining diff exons in a molecular fashion to acquire diff gene products)

tRNA does what to codon

translates the codon into the correct AA

ribosomes

are factories where translation (protein synthesis) occurs

three steps of translation

1. initiation in prok occurs when 30S ribosome attaches to the shine-dalgarno seq and scans for a start codon; it lays down N-formylmethionine in the P site of the ribosome. in euk, 40S ribosome attaches to the 5’ cap and scans for a start codon; it lays down methionine in the P site of the ribosome

2. elongation involves the addition of new aminoacyl-tRNA into the A site o the ribosome and transfer of the growing polypeptide chain from the tRNA pauses in the E site before exiting the ribosome

3. termination occurs when the codon in the A site is a stop codon; a release factor places a water molecule on the polypeptide chain and thus releases the protein

initiation, elongation, and release factors help with each step in recruitment an assembly/disassembly of the ribosome

post translational modifications include: (4)

folding by chaperones

formation of quaternary structure

cleavage of proteins or signal seq

covalent addition of other biomolecules (phosphorylation, carboxylation, glycosylation, prenylation)

jacob-monod model of repressors and activators

explains how operons work

operons

are inducible or repressible clusters of genes transcribed as a single mRNA

inducible systems (like lac operon) vs repressible systems (like trp operon)

inducible: are bonded to a repressor under normal conditions; they can be turned on by an inducer pulling the repressor from the operator site

repressible: are transcribed under normal conditions; they can be turned off by a corepressor coupling with the repressor and the binding of this complex to the operator site

transcription factors

search for promoter and enhancer regions in the DNA

promoters vs enhancers

p: are within 25 base pairs of the transcription start site

e: are more than 25 base pairs away from the transcription start site

modification of chromatin structure affects the ability of…

-what inc accessibility/ dec accessibility to DNA

transcriptional enzymes to access the DNA through histone acetylation (inc accessibility) or DNA methylation (dec accessibility)

how is the immune system divided up

into innate and adaptive immunity

innate immunity

is composed of defenses that are always active, but that cannot target a specific invader and cannot maintain immunologic memory

(nonspecific immunity)

adaptive immunity

is composed of defenses that take time to activate, but that target a specific invader and can maintain immunologic memory

(specific immunity)

the immune system is dispersed throughout the body how (bone marrow, spleen, lymph nodes, thymus, GALT, leukocytes)

immune cells come from the bone marrow

the spleen and lymph nodes are sites where immune response can be mounted and in which B-cells are activated

the thymus is the site of T-cell maturation

gut-associated lymphoid tissue (GALT) includes the tonsils and adenoids

leukocytes or white blood cells are involved in immune defense

many of the nonspecific defenses are noncellular: skin, mucus, tears and loliva, stomach

skin—acts as a barrier and secretes antimicrobial compounds like defensins

mucus—on mucous membranes traps pathogens; in the respiratory system, the mucus is propelled upward by clia and can be swallowed or expelled

tears and saliva—contain lysozyme (an antibacterial compound)

the stomach—produces acid, killing most pathogens. colonization of the gut helps prevent overgrowth by pathogenic bacteria through competition

the complement system

can punch holes in the cell walls of bacteria, making them osmotically unstable

interferons

are given off by virally infected cells and help prevent viral replication and dispersion to nearby cells

nonspecific defenses that are also cellular (macrophages, MHC class I and II, dendritic cells, natural killer cells, granulocytes, neutrophils, eosinophils, basophils)

macrophages—ingest pathogens and present them on major histocompatibility complex (MHC) molecules. they also secrete cytokines

MHC-I—is present in all nucleated cells and displays endogenous antigen (proteins from within the cell) to cytotoxic T-cells (CD8+ cells)

MHC-II—is present in professional antigen-presenting cells (microphages, dendritic cells, soe B-cells, and certain activated epithelial cells) and display exogenous antigen (proteins from outside the cell) to helper T-cells (CD4+ cells)

dendritic cells—are antigen-presenting cells in the skin

natural killer cells—attack cells not presenting MHC molecules, including virally infected cells and cancer cells

granulocytes—include neutrophils, eosinophils, and basophils

neutrophils—ingest bacteria, particularly opsonized bacteria (those with antibodies). they can follow bacteria using chemotaxis

eosinophils—are used in allergic reactions and invasive parasitic infections. they release histamine, causing an inflammatory response

basophils—are used in allergic reactions. mast cells are related cells found on the skin

humoral imunity

is centered on antibody production by plasma cells, which are activated by B-cells

how antibodies function (1):

2 -when activated (hypermutation)

3 -circulating antibodies (opsonization and agglutination)

4 -cell-surface antibodies

5 -memory B-cells (secondary response)

antibodies target a particular antigen. they contain two heavy chains and two light chains. they have a constant region and a variable region (the tip of the variable region is the antigen-binding region)

when activated, the antigen-binding region undergoes hypermutation to improve specificity of the antibody produced. cells may be given signals to switch isotopes of antibody (IgM, IgD, IgG, IgE, IgA)

circulating antibodies can opsonize pathogens (mark them for destruction) cause agglutination (clumping) into insoluble complexes that are ingested by phagocytes or neutralize pathogens

cell-surface antibodies can activate immune cells or mediate allergic reactions

memory B-cells lie in wait for a second exposure to a pathogen and can then mount a more rapid and vigorous immune response (secondary response)

cell-mediated (cytotoxic) immunity and how T-cells undergo maturation

is centered on the functions of T-cells

T-cells undergo maturation in the thymus through positive selection (only selecting for T-cells that can react to antigen presented on MHC) and negative selection (causing apoptosis in self-reactive T-cells). the peptide hormone thymosin promotes T-cell development

helper T-cells (Th or CD4+)

—and specifically the function of Th1 vs Th2

respond to antigen on MHC-II and coordinate the rest of the immune system, secreting lymphokines to activate various arm of immune defense

Th1 cells secrete interferon gamma, which activates macrophages

Th2 cells activate B-cells, primarily in parasitic infections

cytotoxic T-cells (Tc, CTL, or CD8+)

respond to antigen on MHC-I and kill virally infected cells

suppressor (regulatory) T-cells (Treg)

tone down the immune response after an infection and promote self-tolerance

memory T-cells

serve a similar function to memory B-cells

in autoimmune conditions…

a self-antigen is identified as foreign, and the immune system attacks the body’s own cells

in allergic reactions..

nonthreatening exposures incite an inflammatory response

immunization is a method of inducing ___immunity (activation of B-cells that produce antibodies to an antigen) prior to exposure to a particular pathogen

active immunity

passive immunity

is the transfer of antibodies to an individual

the lymphatic system: general structure and function

is a circulatory system that consists of one way vessels with intermittent lymph nodes

equalizes fluid distribution, transports fats and fat soluble compounds in chylomicrons, and provides sites for mounting imune respose

the lymphatic system connects to the cardiovascular system via

the thoracic duct in the posterior chest

fluid mosaic model

accounts for the presence of lipids, proteins, and carbohydrates in a dynamic, semisolid plasma membrane that surrounds cells

plasma membrane contains proteins embedded in…

phospholipid bilayer

how is the membrane not static:

(lipid rafts, flipases, proteins and carbohydrates)

lipids move freely in the plane of the membrane and can assemble into lipid rafts

flippases are specific membrane proteins that maintain the bidirectional transport of lipids between the layers of the phospholipid bilayer in cells

proteins and carbohydrates may also move within the membrane, but are slowed by their relative large size

what is the primary membrane component

lipids are the primary membrane component, both by mass and mole fraction

triglycerols and free fatty acids

act as phospholipid precursors and are found in low levels in the membrane

glycerophopholipids

replace one fatty acid with a phosphate group, which is often linked to other hydrophilic groups

cholesterol

is present in large amounts and contributes to membrane fluidity and stability

waxes

are present in very small amounts, if at all; they are most prevalent in plants and function in waterproofing and defense

proteins located within the cell membrane act as…

transporters, cell adhesion molecules, and enzymes

transmembrane proteins

can have one or more hydrophobic domains and are most likely to function as receptors or channels

embedded proteins

are most likely part of a catalytic complex or involved in cellular communication

membrane associated proteins

may act as recognition molecules or enzymes

glycoprotein coat

carbohydrates can form a protective glycoprotein coat and also function in cell recognition

extracellular ligands and membrane receptors

extracellular ligands can bind to membrane receptors, which function as channels or enzymes in second messenger pathways

cell-cell junctions and membrane transport

3 types: gap and tight junctions, and desmosomes and hemidesmosomes

regulate transport intracellularly and extracellularly

gap—allow for the rapid exchange of ions and other small molecules between adjacent cells

tight—prevent paracellular transport, but do not provide intercellular transport

desmosomes and hemidesmosomes—anchor layers of epithelial tissue together

concentration gradients importance to membrane function

help determine appropriate membrane transport mechanisms in cells

osmotic pressure (and name for type of property)

a colligative property

is the pressure applied to a pure solvent to prevent osmosis and is used to express the concentration of the solution

it is better conceptualized as a “sucking” pressure in which a solution is drawing water in, proportional to its concentration

passive transport

does not require energy bc the molecule is moving down its conc grad. or from an area with higher to lower conc.