Bio HL1 Test 3 - Kim

enzymes

biological catalysts made of proteins (sometimes RNA)

increase biochemical reactions without being consumed or changed

allow rapid metabolic reactions to sustain life

enables homeostasis under changing environmental conditions

prevents accumulation of toxic intermediates

metabolism

complex network of interdependent and interacting chemical reactions in living organisms

consists of anabolism and catabolism

enzymes provide ________

specificity; one catalyzes only one specific type of reaction or a specific substrate

each metabolic pathway consists of

many different enzymes—differences in enzymes determines which pathway occurs and how each is regulated

most enzyme produces only _______ changes

small

significant transformations occur via

a sequence of many enzymatic steps

linear pathway (chain)

proceeds in a single direction with distinct starting and ending molecules—e.g. glycolysis converting glucose into pyruvates  

cyclical pathway (more common)

regenerates starting molecule at end of process, allowing cycle to repeat—e.g. Calvin and Krebs cycle

enzymatic reactions can occur

both inside and outside of the cell

intracellular enzymes

made by free ribosomes and used within cytoplasm—glycolysis—some are used inside organelles—Krebs cycle in mitochondrial matrix

extracellular enzymes

made by bound ribosomes on ER and released from cell—break down larger macromolecules in the gut of digestive system

anabolic reactions

synthesis of complex molecules—monomers → polymers via condensation reaction—e.g. protein synthesis, glycogen formation, photosynthesis—endergonic

endergonic

requires energy, usually from ATP, reactants have less energy then products, more free energy after rxn

catabolic reactions

breakdown of complex molecules into simpler ones—polymers → monomers via hydrolysis—e.g. digestion, cellular respiration—exergonic

exergonic

releases energy that can be captured as ATP, reactants have more energy than products, spontaneous, less free energy after reaction

enzymes are _____ proteins whose ______ arises from folding polypeptides into compact forms

globular; shape

active site

region where substrates bind and reactions occur

enzymes and active sites are

complimentary in shape and chemical property

active sites consist of ____ amino acids

few

three dimensional conformation of entire enzymes

determines active site’s shape and chemical properties

AA interactions distant from active site in primary structure maintain

correct folding necessary for catalytic activity

if any part of an enzyme changes

overall shape and active site may change, and enzyme may lose function

induced fit model

proposes that both enzyme’s active site and substrate undergo slight conformational changes upon bonding, with adjustment increasing surface area and precision of fit, ensuring greater catalytic efficiency by positioning substrate in optimal orientation, lowering activation energy and increasing reaction potential

Brownian motion

molecules move randomly in cell environments (aqueous) due to kinetic energy, substrate and active site must collide with correct orientation and sufficient energy for binding and reaction to occur, some larger substrates are immobilized, or fixed, so enzymes must approach them, sometimes enzymes are immobilized due to membrane attachment so substrates must diffuse towards them

metabolic reactions convert energy from food

into ATP, but transfer of energy is never fully efficient, and some energy is lost in the form of heat (in mitochondria during respiration)

mammals and birds (endotherms) use heat

to maintain constant body temp—essential for homeostasis, ensuring optimal conditions for enzymatic activity and survival; if not enough is produced, metabolic rate increases

some enzymes are absolutely _____, while others are less _____.

specific and bind to only one substrate; specific and bind to a group of substrates

denaturation

loss of enzyme’s specific structure due to environmental factors like temp, pH, or concentration; its usually irreversible and results in loss of function

increase in thermal energy leads to

increased kinetic NRG → increased particle motion → increased collisions → increased reaction rate

lower temperatures on enzymes

lowers reaction rate but doesn’t denature

increasing substrate concentration

results in an increase in enzyme activity and therefore reaction rate, because increasing substrates allows for more frequent collision with enzymes, at some point the reactions plateau because all active sites are occupied or “saturated,” and the reaction has reached Vmax of maximum rate

activation energy

minimum energy required to break bonds in a reactant and initiate a chemical reaction—enzymes increase reaction rate by decreasing activation energy, temporarily binding to substrate to stress and destabilize bonds, less overall energy is required, increasing reaction rate, net amount of free energy in reaction stays the same

enzymes work as templates by

allowing substrates to reach optimal orientation and place stress on necessary bonds, functioning as suitable microenvironments by maintaining optimal pH

non-competitive inhibitor

binds to allosteric site that is separate from active site—only specific molecules (allosteric regulators) can bind here, changes overall shape of enzyme and therefore its active site—increasing concentration does not overcome inhibition, binding is mostly reversible

competitive inhibitor

substrate and inhibitor are structurally and chemically similar and compete for the same active site, increasing substrate [] reduces or overcomes inhibition because substrates outcompete for active site, normally reversible, covalently bonded inhibitors are not

statins

drug that acts as a competitive inhibitor of HMG-CoA reductase (enzyme involved in cholesterol synthesis), resembles HMG-CoA and binds to active site, decreases cholesterol production in liver cells—higher [HMG-CoA] can partially overcome inhibition

end product inhibition

control mechanism in which end product of a metabolic pathway inhibits an earlier enzyme by binding to its allosteric site, preventing overproduction of end product and conserving energy—once product levels decrease, inhibitor dislodges and pathway resumes

example of end product inhibition

isoleucine as inhibitor for threonine—threonine→intermediate compounds→ isoleucine—isoleucine is a noncompetitive inhibitor for threonine deaminase

mechanisms based inhibition

inhibitor permanently binds to active site with covalent bond, rendering it irreversibly inactive—e.g. penicilin—antibiotic that targets transpeptidase enzyme, responsible for cell wall synthesis, some bacteria have evolved mutations in the gene that codes for transpeptidase, causing structural changes in the active site, and penicillin can’t bind effectively, preventing covalent bonds (how resistance develops)

homeostasis

maintenance of a stable internal environment

homeostasis is achieved through

monitoring and initiating corrective responses that keep organism within preset tolerance limit

general homeostatic process

stimulus - change in internal variable

receptor - detects deviation from set range

control center - compares changed value to set range

effector - restores variable to normal range via negative feedback

homeostatic factors in humans

body temperature: 36-38 C

blood pH 7.35-7.45

blood glucose [] 75-96 mg/dl

blood osmotic [] varies depending on body size

negative feedback

control mechanism that detects changes in variable and responds to reverse the changes, returning body to set range to restore equilibrium, corrects deviations both above and below range, positive feedback amplifies changes and moves variables from further range, creating instability

endocrine system

signal via hormones, transmission via blood released from endocrine glands, targets cells with complimentary receptors in any tissue type, speed is slower and effects last longer, until hormone is broken down

pancreas

both:

an exocrine (duct) gland, secreting digestive enzymes into small intestines

an endocrine (ductless) gland, secreting glucagon and insulin into bloodstream

Islet of Langerhans

group of cells in pancreas, alpha cells produce glucagon when blood glucose falls below set range, target cells in liver converts glycogen to glucose, adipose tissue breaks down fat (glucose production from non-glycogen sources), blood glucose [] increases

nervous system

signal: electrochemical, transmitted via synapse between neurons, not through blood, targets specific cells, typically muscles or glands, speed is very fast, effects are short-lived (e.g. reflex arc)

role of blood in transporting materials

enables coordination between organs that cannot communicate directly, transports hormones from endocrine glands to target organs, circulates nutrients, gases, and wastes to maintain homeostasis (e.g. glucose, O2/CO2 and energy)

beta cells produce

insulin, when blood glucose rises above set range, targets liver and skeletal muscles and converts glucose to glycogen, adipose tissue increases glucose uptake for fat synthesis, decreases blood glucose []

glucose and insulin transport

hormones enter blood vessels around pancreas, circulate around body, dissolved in blood, makes contact with target cells that have complimentary receptors

diabetes mellitus

characterized by elevated blood glucose during prolonged fasting, symptoms include presence of glucose in urine and persistent thirst, impaired water re-absorption during urine production, leads to dehydration

type 1 diabetes

inability to produce insulin, autoimmune disorder in which beta cells are destroyed, appears during childhood, physiological changes include loss of Beta cells in Islet of Langerhans, little or no insulin secretion, chronically high blood glucose (hyperglycemia)

risk factors include genetic predisposition, autoimmune susceptibility, no known prevention, treatment includes continuous glucose monitoring and insulin injections, implant devices that release exogenous insulin

type 2 diabetes

caused by an inability to respond to insulin, metabolic disorder due to insulin resistance, where target cells respond weakly to insulin, physiological changes include reduced sensitivity in muscle and liver cells, decreased glucose uptake despite normal insulin production, and eventual beta cell fatigue and reduced insulin output

risk factors include obesity and sedentary lifestyle, diets high in refined carbohydrates and low in fiber, age, genetics, and chronic stress, can be prevented by regular physical activity, balanced diet rich in whole grains, fruits, and vegetables, and maintaining a healthy bodyweight

treatment includes lifestyle modification (diet and exercise), small amounts of food eaten frequently, metformin and other medications to increase insulin sensitivity

hypothalamus

detects changes in internal conditions (blood glucose, temperature, water levels), and produces specific releasing or inhibiting hormones to stimulate the pituitary gland

pituitary gland

located directly below the hypothalamus, responds to hypothalamus by increasing/decreasing the release of specific hormones into blood (negative feedback)

anterior pituitary releases

TSH (thyroid stimulating hormone) for thermoregulation

FSH and LH (follicle stimulating hormone and luteinizing hormone) for reproductive regulation

posterior pituitary releases

ADH (antidiuretic hormone) for osmoregulation

oxytocin for uterine contractions and milk production

thermoregulation

maintenance of internal body temperature within a narrow, stable range (37 C) despite external changes, regulated by negative feedback, monitored by peripheral thermoreceptors, sensory nerve cells located in skin and mucosal linings, detects external temperature changes (hot and cold), anticipates heat loss, and sends signals to hypothalamus to restore set range, to which hypothalamus activates negative feedback

pituitary gland releases TSH, causing

a stimulation to the thyroid gland to release thyroxine

thyroxine

hormones that increase metabolic rate in tissues, production increases in cold and decreases in hot conditions, all cells respond but the main effectors are skeletal muscles that shiver to generate heat, and brown adipose tissues that increase metabolic activity

vasodilation

widening of arteries that supply blood to skin, lumen widens → more blood flows to skin surface → more heat lost

sweating

secretion of fluid by sweat glands onto skin surface, provides evaporative cooling as water molecules with most thermal energy become vapor

responses to heat

vasodilation and sweating

responses to cold

vasoconstriction, uncoupled respiration of brown adipose tissue, hair erection, and shivering

vasoconstriction

narrowing of arteries that supply blood to skin → lumen narrows → less blood flows to skin surface → less heat lost

shivering

rapid, involuntary skeletal muscle contractions, increased metabolic activity causes heat as by-product

uncoupled respiration of brown adipose tissue

usage of specific mitochondrial proteins allow proton flow without ATP production during cellular respiration, releases heat as a byproduct (brown due to increased presence of mitochondria)

hair erection

contraction of arrector pili muscles attached to hair follicles, raises hairs to trap a thin layer of air near skin, ineffective in humans due to reduced body hair, produces goosebumps now

circadian rhythm

internal 24-hour biological cycle that regulates physiological processes, monitored by suprachiasmatic nuclei (SCN) in hypothalamus, signals pineal gland to produce melatonin, hormone that controls wake-sleep cycle, without light, circadian rhythm is slightly longer than 24 hours, but it is synchronized with daily cycle via light, disruptions like jet lag or night work can misalign circadian rhythm

melatonin patterns

low during daylight, retina detects sunlight, signals SCN → inhibits melatonin, as day progresses, amount of light decreases, signals SCN → produces melatonin, highest during night—maintains drowsiness and supports sustained sleep, contributes to nighttime decrease in core body temp and urine production, as night progresses, amount of light increases, signals SCN → inhibits melatonin

epinephrine

hormone and neurotransmitter secreted by adrenal glands located on top of kidneys, prepares body for vigorous physical activity in response to perceived threats or danger

epinephrine’s effect on circulatory system

increases heart rate and stroke volume, enhancing cardiac output, causes vasodilation in arterioles to muscles and liver to increase blood flow (increasing O2 and glucose)

causes vasoconstriction in arterioles to gut and skin to decrease blood flow to non-essential areas

epinephrine’s effect on respiratory system

dilate bronchi and bronchioles (smooth muscle) to increase air intake and delivery to alveoli, increases ventilation rate to increase O2 intake and CO2 removal

epinephrine’s effect on muscle system

increases Ca2+ availability to increase force of contraction, also increases speed of contraction, recieves more O2 and glucose due to increased blood flow, supporting aerobic and anaerobic metabolism

epinephrine’s overall impact on muscle contraction

coordinates circulatory, respiratory, metabolic, and muscle system to maximize energy supply, rapidly mobilizes glucose and fatty acids to support sustained ATP production, improves O2 delivery and removes metabolic wastes to allow strong, prolonged muscle contraction

digestion

processes under voluntary control of central nervous system (brain and spinal cord), initiation of swallowing, voluntary action of tongue (muscle) pushes food to back of mouth, touch receptors in pharynx allow swallowing

egestion

removal of undigested food as féces, relaxation of anál sphincter (ring of smooth muscle), allows rectúm to push

digestion and egestion are processes under involuntary control of

the enteric nervous system—a network of neurons in the gut wall that controls involuntary digestive functions without input from CNS like peristalsis

peristalsis

rhythmic waves of smooth muscle contractions, moving food continuously in one direction from esophagus to rectum, allows absorption in small intestines

kidneys

major organ for osmoregulation and excretion, outer region is cortex, innter is medulla, nephron is basic functional unit

kidney’s osmoregulation

maintenance of stable osmotic concentration (unit osmol L^-1)

regulates movement of H2O by controlling solute []

kidney’s excretion

removal of toxic waste products of metabolism, from digestion of nitrogen containing foods like proteins and nucleic acids, main waste is urea

ultrafiltration and its location

non-specific filtration of solutes from blood into nephron using hydrostatic pressure; located in glomerulus (blood) and Bowman’s Capsule, filters out most blood plasma except cells and proteins

glomerulus (cortex)

ball-shaped network of capillaries, blood moves from renal artery → afferent arterioles → glomerulus (capillaries) → efferent arterioles → renal vein

causes of ultrafiltration

afferent arterioles diameter is greater than efferent arterioles diameter, creating pressure

twisted route that blood takes also creates pressure

capillaries are fenestrated (highly porous)

Bowman’s capsule (cortex)

walls are made of podocytes (cells), between glomerulus and podocytes is basement membrane—prevents blood cells and proteins from passing through, ultrafiltration occurs mostly based on size

capsule recieves glomerular filtrate produced by ultrafiltration, fluid forced out of glomerulus into nephron, ensuring one-way flow into proximal convulated tubule

Selective Reabsorption (where, and what happens?)

mainly in Proximal convoluted tubules, selectively uptakes necessary materials back from filtrate into blood

Proximal convoluted tubule (cortex)

epithelium is one-cell thick, joined by tight junction, lined with microvilli inside which increases absorption 5x, many mitochondria for active transport

reabsorbed materials travel from lumen of proximal tubule → epithelial cell (lining) → interstitial fluid → capillaries surrounding nephron—active transport returns most ions (Na+) to blood, co-transport moves glucose and AA against [] then facilitated diffuses into blood, osmosis returns H2O, follows established solute []

urea, toxins, and other unwanted solutes remain in filtrate

Distal convoluted tubule

mimics processes in PCT to make fine adjustments, filtrate [] is hypotonic

Osmoregulation

in loop of Henle, done to establish and maintain a high solute [] in medulla to enable H2O reabsorption in collecting duct

countercurrent multiplier system

kidney establishes salt gradient, salt [] in interstitial fluid of kidney becomes increasingly greater (more hypertonic) from cortex to medulla, loop of Henle and blood surrounding move in opposite directions (counter-current), salt gradient allows H2O to be retained in blood more efficiently, creates hypertonic urine

ascending limb of loop of henle

permeable to salt but not H2O, actively pumps out Na+, Cl- follows, establishes and maintains medulla’s steep [] gradient, filtrate [] decreases

descending limb of loop of henle

permeable to H2O, H2O moves out into medulla via ososis using aquaporins, medulla becomes increasingly [], so H2O can continuously move out, filtrate [] increases

osmoregulation in final region

final region where H2O reabsorption occurs

Collecting duct (medulla)

moves filtrate (urine) to renal pelvis, which empties via ureter to bladder, permeable to H2O, H2O moves out depending on ADH, permeable to urea in medulla, also increases osmolarity, filtrate [] increases

antidiuretic hormone (ADH)

osmoreceptors (neurons) in hypothalamus detect change in osmomolarity of blood to determine degree of H2O reabsorption, ADH regulates H2O permeability in collecting duct via number of aquaporins, increases blood osmolarity (too little H2O), signals posterior pituitary to increase ADH production, decreases blood osmolarity (too much H2O), decreases ADH production

aquaporins

membrane protein channels that facilitate H2O diffusion, stored in intracellular vesicles when unused, high ADH—binds to receptors on cells of collecting duct, triggers vesicles containing aquaporins to fuse with cell membrane, increased membrane permeability to H2O, produces smaller amounts of more concentrated urine, also feels thirst

once hydrated, low ADH; endocytosis removes aquaporins from membrane to intracellular vesicles, decreased membrane permeability to H2O, produces larger amounts of diluted urine