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mcat bio


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What are the differences between a compound light microscope, a phase contrast microscope, and an electron microscope?
Compound light: - Uses two lenses or lens systems to magnify an object - Non-living specimens because it requires contrast by staining (kills cells) Phase contrast: - Study of living cells using differences in refractive index between cellular structures Electron microscope: - Uses beam of electrons to allow 1000x higher magnification - Non-living only
How are different cellular structures separated by centrifugation?
High density: - Ribosomes Low density: - Mitochondria - Lysosomes
What are the main, major differences between prokaryotes and eukaryotes?
P: - Unicellular - Have cell membrane, but no membrane-bound organelles - No nucleus - DNA is circular, also may have plasmids - Have cell wall, cytoplasm, ribosomes - Respiration E: - Bounded by cell membrane + cytoplasm - Contains membrane-bound organelles - DNA organized into chromosomes, located in nucleus - Cell wall (only in plants/fungi) - Centrioles (only in animals)
Describe the permeability of the plasma membrane.
- Readily permeable to small non-polar molecules and SMALL polar molecules (water) - Most polar molecules cannot cross the membrane (require carrier proteins)
Describe the functions of the smooth and rough ER.
Rough ER: - Protein synthesis Smooth ER: - Detoxification of drugs/poisons - Lipid synthesis
What is unique about the enzymes of the lysosome?
- Function the best at a pH of about 5 - The environment inside the lysosome is acidic
What are the basic characteristics of an enzyme?
- Lower the activation energy of a reaction (kinetics) - Increase the RATE of a reaction - Do NOT affect overall dG (delta G) of the reaction - Are not changed or consumed during the reaction
Describe the relationship between Km and [S] (in terms of reaction rate and enzyme affinity).
When: 1) Km = [S] --> Rate = 1/2 Vmax. This is the substrate concentration at which half of the enzyme's active sites are filled 2) When [S] < Km --> changes in [S] greatly affect the rate. 3) When [S] > Km --> V approaches Vmax, and the rate cannot be increased that much more. ** Enzyme affinity can be assessed by Km: - A low Km reflects a HIGH affinity for the substrate
Describe the differences between competitive and noncompetitive inhibitors of enzymes.
Competitive: - Bind directly to active site - Can be overcome by adding more substrate Noncompetitive: - Do NOT bind to active site, but to another site on enzyme - Enzyme can no longer bind substrate at active site - Cannot be overcome by increasing substrate concentration
Describe the roles of ATP, NAD+, NADP+, and FAD as energy carriers in cellular metabolism.
ATP: - Energy stored in covalent bonds that attach the phosphate groups NAD+, NADP+, and FAD: - Store energy in the form of high potential e- - The e- are transferred as hydride ions (H-) - All of these are oxidizing agents, and therefore are themselves reduced when they gain H- ions (reduced during catabolic processes)
Describe the important parts of glycolysis.
- Occurs in cytoplasm - Glucose is oxidized into two molecules of pyruvate - Generates 2 ATP (net), 2 NADH, and 2 pyruvate
Describe the different types of fermentation that occur in anaerobic conditions.
Alcohol fermentation: - Commonly occurs in yeast and bacteria - Pyruvate is reduced to ethanol (using NADH) - This regenerates NAD+ Lactic acid fermentation: - Occurs in fungi, and in human muscle cells - Pyruvate is reduced to lactic acid - NAD+ is regenerated
Describe the important parts of cellular respiration.
Pyruvate decarboxylation: - Occurs in the mitochondrial matrix - Pyruvate loses CO2 to form acetyl CoA - NADH is generated Kreb's cycle: - Also in the mitochondrial matrix - Each turn produces 1 GTP, 1 FADH2, and 3 NADH - CO2 is also released Electron transport chain: - Chain located in inner mitochondrial membrane - The high-energy electrons are transferred from NADH and FADH2 to oxygen - As electrons are transferred between carriers, energy is released and ATP is formed
Describe the process of ATP formation by the electron transport chain.
- As NADH and FADH2 pass their e- to the ETC, free H+ ions are released and accumulate in the mitochondrial matrix - The ETC pumps the ions out of the matrix into the intermembrane space - This creates a positively charged acidic environment in the intermembrane space - This electrochemical gradient creates a proton-motive force that drives H+ back across the inner membrane, into the matrix - To pass through the membrane, H+ ions must flow through ATP synthetases - As the H+ ions pass through, ADP is phosphorylated to ATP
Describe the 3 alternate energy sources in the body (besides glucose).
1) Carbs - Disaccharides can be hydrolyzed into monosaccharides, which can be converted into glucose or its intermediates 2) Fats - Stored in adipose tissue - Fatty acids undergo beta-oxidation 3) Proteins - AAs can undergo transamination - Can enter citric acid cycle
What is the pathway of sperm in the male reproductive system?
S - seminiferous tubules E - epididymis V - vas deferens E - ejaculatory duct N U - urethra P - penis
Describe the anatomy of the male gonads.
The male gonads are the testes: 1) Seminferous tubules - create sperm 2) Interstitial cells - secrete testosterone and other androgens
Describe the process of spermatogenesis.
Spematogonia (2N) --> 1* spermatocytes (2N) --> 2* spermatocytes (N) --> spermatids (N) --> spermatozoa (N)
Describe the anatomy and functions of the female gonads.
The female gonads are the ovaries - Produce ovum (eggs) - Contain follicles, which produce estrogen - Produce and secrete progesterone
Describe the path of a released ovum
- Every month, an ovum is released from a follicle, into the fallopian tube - The fallopian tube contains cilia that beat towards the uterus, pulling the ovum towards the uterus - If fertilization is to occur, it will occur in the fallopian tube - The fertilized zygote will implant in the uterine wall
Describe the process of oogenesis.
- At birth, all of the primary oocytes a woman will make are already formed - They are all arrested in prophase I of meiosis I - After menarche, one 1* oocyte per month undergoes meiosis I, releasing a 2* oocyte - The 2* oocyte only undergoes meiosis II if fertilized
Describe the process of fertilization in humans.
- Occurs in the fallopian tube - Sperm penetrate the corona radiata using enzymes it secretes - The acrosome aids in penetrating the zona pellucida
Describe the "cleavage" stage of embryonic development (until formation of blastula).
- Series of rapid mitotic divisions occur (but cytoplasm volume remains the same) Morula = solid ball of embryonic cells created during rapid cleavage Blastulation = morula develops a fluid-filled cavity called the blastocoel - Blastula = hollow sphere of cells containing an inner cell mass and a trophoblast
Describe the process of implantation during embryonic development
- Embryo implants in uterine wall during blastulation - Uterus is prepared for implantation by PROGESTRONE --Causes glandular proliferation in the endometrium - This eventually becomes the site of the placenta
Describe the processes that occur during gastrulation.
Gastrulation = formation of the 3-layered gastrula after implantation - Archenteron = cavity of the gastrula which forms the gut - Blastopore = opening of archenteron, future site of the anus)
Describe the structures associated in the development of the placenta.
Amnion = membrane containing amniotic fluid - Fluid acts as shock absorber during labor Chorion = membrane surrounding amnion - Chorionic villi extend into uterine wall, developing into spongy tissue of placenta Allantois = this structure's blood vessels enlarge and become the umbilical vessels Yolk sac = Site of early development of blood vessels, becomes associated with umbilical vessels Umbilical cord is formed by enveloping of the yolk sac and the allantois by the amnion
Name and describe the 3 different shunts in fetal circulation.
Ductus venosus = shunts blood away from fetal liver Foramen ovale = shunts most blood entering the right atrium into left atrium (so it can bypass pulmonary circulation) Ductus arteriosus = shunts MOST of the blood that does enter the pulmonary artery directly into the aorta, again bypassing the fetal lungs **Some blood STILL goes to the lungs, but this blood only nourishes the developing lung tissue
What are the only arteries that carry deoxygenated blood, and the only veins that carry oxygenated blood?
The adult pulmonary artery and the fetal umbilical artery --> carry oxygenated blood The adults pulmonary vein and the fetal umbilical vein --> carry deoxygenated blood
What occurs during each of the 3 trimesters of gestation?
1st trimster: - Development of major organs - Formation of eyes, gonads, limbs, and liver - Cartilaginous skeleton turns into bone - Brain is fairly developed 2nd trimester: - Rapid growth, begins to move around - Fingers and toes elongate 3rd trimester: - Rapid growth - Further brain development
Describe the structure and formation of cartilage.
- Connective tissue that is softer than bone Composed of chondrin: - Firm, elastic matrix - Secreted by chondrocytes
What is the difference between compact and spongy bone?
Compact bone: - Dense bone - Does not appear to have any cavities Spongy bone: - Less dense - Interconnecting lattice - Yellow and red bone marrow fills the cavities
Describe the anatomy of the long bones.
Diaphysis = long, cylindrical shaft - Contains a cavity of bone marrow Epiphyses = dilated ends of the shaft Epiphyseal plate = disk of cartilaginous cells, site of longitudinal growth
Describe the microscopic bone structure
Bone matrix composes the bone - Consists of organic and inorganic components Osteoblasts = build bone Osteoclasts = bone resportion (destroying bone)
Describe the two types of bone formation.
Endochondral ossification = process of turning cartilage into bone Intramembranous ossification = mesenchymal cells are transformed into bone
Describe the important features of skeletal muscle.
- Innervated by somatic nervous system - Multinucleated - Striated (contains sarcomeres) - Voluntary contraction - Uses ACh (only excitatory)
Describe the structure of the sarcomere.
- Composed of thin (actin, troponin, tropomyosin) filaments - Composed of thick (myosin) filaments Z-lines - anchor the thin filaments M-line - runs down center of sarcomere I-band - region containing only thin filaments (contains Z-line) A-band - length of thick filaments H-zone - region containing thick filaments only (contains M-line)
Describe the events that occur during contraction of skeletal muscle.
1) Initiation - Motor neuron sends message to muscle fiber - Message transfer occurs at NMJ via use of ACh 2) Shortening - Once AP is generated, it is conducted along the T-system - SR releases calcium - Calcium binds to troponin, causing tropomyosin to shift, and exposing the myosin-binding sites on the thin filaments - Myosin binds to actin, forming cross bridges - Power stroke occurs 3) Relaxation - Calcium is pumped back into SR - ADP and Pi are released from the myosin heads Tropomyosin now covers the myosin-binding sites
Describe the important features of smooth muscle.
- Involuntary actions - Innervated by autonomic nervous system - Not striated - Contraction regulated by calcium - Excitatory and inhibitory
Describe the important features of cardiac muscle.
- Striated (contains sarcomeres) - Innervated by autonomic nervous system
Describe the process of digestion in the oral cavity.
- Mechanical and chemical digestion occurs here - Large food particles are broken down into smaller particles - Saliva contains salivary amylase --> hydrolyzes starch into simple sugars
Describe the pathway of food in the digestive system.
Mouth --> pharynx --> esophagus --> stomach --> small intestine --> large intestine
What is the covering of the trachea that prevents food from entering this tube?
The epiglottis
What is the muscle that regulates transfer of food from the esophagus to the stomach?
The lower esophageal sphincter (or cardiac sphincter).
Describe the processes of digestion in the stomach.
Walls of stomach contain: 1) Gastric glands: composed of 3 types of cells - Mucous cells secrete mucus, protecting the stomach from the acidic juices - Chief cells secrete pepsinogen, the zymogen of pepsin (protein-hydrolyzing enzyme) - Parietal cells secrete HCl, which kills bacteria and activates pepsin 2) Pyloric glands: secrete gastrin - Stimulates release of more HCl - Stimulates muscular contractions of the stomach (produces chyme)
What is the muscle that regulates passage of chyme from the stomach into the small intestine?
The pyloric sphincter
Describe the anatomy of the small intestine.
Divided into three sections: - Duodenum (most digestion) - Jejunum (most absorption) - Ileum (most absorption) Villi - numerous finger-like projections that increase the surface area
Describe the digestive functions of the small intestine.
Mostly occurs in the duodenum - Carbohydrates are digested by enzymes - Proteins hydrolyzed by peptidases Secretin = hormone released by the presence of chyme - Triggers release of pancreatic juice from pancreas - Pancreatic juice is alkaline fluid that provides the basic environment for small intestine enzymes CCK = secreted in response to chyme - Stimulates release of bile - Enterogastrone = secreted if chyme isp articularly fatty - Inhibits stomach peristalsis, slowing down release of chyme
What are the contents of the pancreatic juice?
Trypsinogen = zymogen of trypsin - Enterokinase activates trypsin - Trypsin hydrolzyes proteins Chymotrypsinogen = zymogen of chymotrypsin - Activated by trypsin - Cleaves peptide bonds - Pancreas also secretes carboxy- and aminopeptidase
Describe the synthesis, storage, release, and function of bile.
Synthesis = in liver Storage = in gallbladder Release = into duodenum in response to CCK Function: - Emulsifies fat globules - Surrounds and maintains the particles in micelles - Exposes more surface area to lipases
Describe the absorptive functions of the small intestine.
Majority occurs in jejunum and ileum Monosaccharides: absorbed via active transport and facilitated diffusion Amino acids: absorbed via active transport ^^ Both enter portal circulation via hepatic portal vein Fatty acids, glycerol, and cholesterol: packaged into chylomicrons and secreted into lymph vessels called lacteals - Transported via lymph to venous blood at the thoracic duct - Bypass processing by the liver Vitamins are absorbed: - Fat-soluble ones (A,D,E,K) are absorbed with fats - Water-soluble ones (B and C) are absorbed via simple diffusion
Describe the absorptive functions of the large intestine.
- The colon functions in the absorption of salts and any water not already absorbed - The rectum stores feces
Name all of the valves that regulate flow in the heart.
Atrioventricular valves: - Tricupsid valve = valvue between the RV and RA - Mitral valve = valve between the LV and LA Aortic valve = between the LV and aorta Pulmonic valve = between the RV and the pulmonary artery
Describe the composition of blood.
Plasma = liquid portion of blood - Mixture of nutrients, salts, gases, wastes, hormones, and proteins Cellular components of blood: - Erythrocytes - Leukocytes - Platelets
Describe the important features of erythrocytes.
Red-blood cells - Contain hemoglobin - Have disk-like shape which gives increased surface area and greater flexibility for movement through capillaries - LACK MITOCHONDRIA
Describe the important features of leukocytes.
- Arise from stem cells in long bone marrow Lymphocytes = one type of leukocyte - Play important role in immune response - Consist of B and T lymphocytes
Describe the movement of CO2 through the blood (regarding its effect on Hb)
CO2 diffuses into the blood (into RBCs) from tissue - In RBCs, it combines with H2O to form carbonic acid - Carbonic acid dissociates into HCO3- and H+ - The HCO3- floats freely in the plasma - In the alveoli, HCO3- and H+ recombine to form carbonic acid, which then dissociates into H2O and CO2 - CO2 is exhaled through the lungs
What is the Bohr effect?
The allosteric relationship between [CO2], [H+], and [O2] - Increasing [CO2] and [H+] (decrease pH) decrease Hb's affinity for O2 - Presence of high [CO2] or [H+] enhances release of O2 to tissues - Increase in these concentrations thus causes a RIGHT shift in the Hb curve
Define humoral and cell-mediated immunity. Which cells are responsible for both of these types of immunity?
Humoral immunity = production of antibodies Cell-mediated immunity = cells that combat fungal and viral infection ** Lymphocytes are responsible for both types
What are antibodies (and what is another term for them)? How do they work?
Antibodies (or immunoglobulins) are proteins that recognize and bind to specific antigens and trigger the immune system to remove them - Attract other cells to phagocytize the antigen - Cause the antigens to clump together and form large, insoluble complexes
Describe the B lymphocytes (what response are they involved in, where do they originate, etc.)
B-cells -- lymphocytes involved in humoral response - Originate in bone marrow and differentiate in the spleen and lymph nodes
Describe the humoral response (how it works, what cells are involved, etc.).
B-cells are involved in the humoral response - Proliferate when exposed to antigen Primary response: Some B-cells become memory cells, and others become plasma cells - Plasma cells produce and release antibodies Secondary response: more specific response elicited by memory cells upon subsequent exposure to an old antigen
Describe the T-lymphocytes (what response are they involved in, where do they originate, etc).
T-cells are involved in cell-mediated immunity - Develop in bone marrow - Mature and proliferate in thymus (T)
Describe the body's cell-mediated immunity (how it works, what cells are involved, what specifically it defends against, etc).
T-cells differentiate into different effector cells: - Cytotoxic T cells = destroy antigens directly - Helper T cells = activate other B and T cells - Suppressor T cells = regulate other B and T cells to decrease their activity T-cells play important roles in: - Allergic reactions - Rejection of organ transplants
List 5 of the body's non-specific defense mechanisms.
- Skin - Mucous-coated epithelia that line passages - Macrophages that engulf and destroy foreign particles - Inflammatory response (initiated in response to physical damage) - Interferons (proteins produced by cells under viral attack)
Describe the important features of the lymphatic system.
- Secondary circulatory system distinct from CV circulation - Transport excess ISF (lymph) to CV system - Keeps fluid levels in body ocnstant
Name the 5 units of the kidney tubule (in order).
1) Proximal convoluted tubule 2) Descending limb of loop of Henle 3) Ascending limb of loop of Henle 4) Distal convoluted tubule 5) Collecting duct
Describe the selective permeability of the nephron (what substances is it permeable to, and where?).
Water permeable at: - Proximal tubule - Descending limb of loop of Henle - Collecting duct (only in presence of ADH) Salt: - Ascending limb only - Everywhere else by active transport
Describe the osmolarity gradient in the kidney.
Tissue osmolarity increases from cortex down to the inner medulla.
Describe the specifics of the flow of filtrate through the nephron.
1) Enters Bowman's capsule and flows into proximal convoluted tubule - All glucose, AAs, and other important organic molecules are reabsorbed - 60-70% of Na+ is reabsorbed - Water and Cl- passively follow 2) Flows down descending limb into renal medulla - Increasing osmolarity here - More water is reabsorbed 3) Flows through ascending limb - Impermeable to water 4) Flows into distal tubule then to collecting duct - H2O reabsorption in duct is under ADH control Urine is hypertonic to the blood (less water, more solute)
What are the two hormones that regulate urine formation?
1) Aldosterone 2) ADH
Describe the function of aldosterone in regulating urine formation.
- Produced by adrenal cortex - Regulated by renin-angiotensin system in response to changes in blood volume (pressure) - Stimulates reabsorption of Na+ and secretion of K+ - Na+ reabsorption causes H2O reabsorption - Leads to a rise in blood volume and blood pressure
Describe the function of ADH in regulating urine formation.
- Formed in hypothalamus and stored in posterior pituitary - Increases water reabsorption by acting directly on the collecting duct to increase its permeability to water ADH secretion is dependent on plasma osmolarity - Increased plasma osmolarity causes ADH secretion
List the important functions of the liver.
Helps regulate blood glucose levels - Can store glucose in form of glycogen - Can also convert glycogen to glucose for release into blood - Can perform gluconeogenesis Produes urea Detoxifies toxins Stores iron Synthesizes bile Beta-oxidizes fatty acids
List and describe the functions of the direct hormones secreted by the anterior pituitary.
1) Prolactin -- stimulates lactation, milk production 2) Endorphins -- inhibit the sensation of pain 3) Growth hormone: - Promotes bone and muscle growth - Conserves glucose - Stimulated by GHRH - Inhibited by somatostatin
List and describe the function of the anterior pituitary's tropic hormones.
1) FSH - Stimulates follicle maturation (females) - Stimulates seminiferous tubule maturation and sperm production (males) 2) LH - Stimulates ovulation and formation of corpus luteum (females) - Stimulates interstitial cells to make testosterone (males) 3) ACTH - Stimulates release of glucocorticoids from adrenal cortex 4) TSH - Stimulates uptake of iodine and secretion of TH from the thyroid glands
Name the hypothalamic hormones that regulate each of the pituitary gland hormones.
1) GH -- regulated by GHRH 2) FSH -- regulated by estrogen and GnRH 3) LH -- regulated by estrogen, progesterone, and GnRH 3) ACTH -- regulated by CRF 4) TSH -- regulated by TRH
List and describe the functions of the hormones released by the posterior pituitary.
1) Oxytocin - Increases strength of contractions during labor 2) ADH - Increases permeability of collecting duct to water - Increases water reabsorption and concentrates the urine - Regulated by osmoreceptors in hypothalamus and baroreceptors in circulatory system
What are the hormones secreted by the thyroid gland? (3)
- Thyroxine (T4) - Triiodothyronine (T3) - Calcitonin
Describe the functions of the thyroid hormones (T3 and T4). Also, what are the problems associated with too much or too little TH?
- Necessary for growth and neurological development of children - Increase rate of cellular respiration and rate of protein and fatty acid synthesis and degradation - Hypothyroidism results in slowed HR, fatigue, weight gain, etc. - Cretinism is hypothyroidism in infants
Describe the function of calcitonin.
DECREASES (tones down) plasma [calcium] - Decreases bone resorption
What hormone does the parathyroid glands secrete? And what is its function?
Parathyroid hormone (PTH) - RAISES plasma [calcium] - Stimulates calcium release from bone

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