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