Biology. MCAT. FOUNDATION REVIEW. COMPANION BOOKLET. MM3260A. *. *
MCAT is a registered trademark of the Association of American Medical ...
FOUNDATION REVIEW COMPANION BOOKLET
MCAT
*
Biology
*MCAT is a registered trademark of the Association of American Medical Colleges.
MM3260A
©2003 Kaplan, Inc. All rights reserved. No part of this book may be reproduced in any form, by photostat, microfilm, xerography or any other means, or incorporated into any information retrieval system, electronic or mechanical, without the written permission of Kaplan, Inc. This book may not be duplicated or resold, pursuant to the terms of your Kaplan Enrollment Agreement.
BIOLOGY 1
Foundation Review
FOUNDATION REVIEW
CELL STRUCTURE AND ORGANIZATION
Cell Theory All living things are composed of cells The cell is the basic functional unit of life Cells arise only from preexisting cells Cells carry genetic information in the form of DNA. This genetic material is passed from parent cell to daughter cell.
Prokaryotes vs. Eukaryotes
No
Yes
DNA-single circular chromosome
DNA-linear chromosomes
Yes
Yes (plants) / No (animals)
Yes
Yes
No
Yes
Yes
Yes
1.
MCAT: BIOLOGY
Draw the following diagram on the board as you discuss organelles:
mitochondria
vesicle
ER smooth rough ribosome
Surrounded by a nuclear membrane; controls the activity of the cell; contains the chromosomes (which are composed of DNA and histone proteins); contains nucleolus which is the site of transcription. Ribosomes Site of protein synthesis (translation); consist of two subunits; made from rRNA and proteins; found on rough ER and in cytoplasm.
Endoplasmic reticulum Network of membrane enclosed spaces connected at points with the nuclear membrane; there are two forms: smooth ER (lipid synthesis and detoxification of drugs and poisons); and rough ER (protein synthesis, contains ribosomes) Golgi apparatus Stack of membrane-enclosed sacs; functions in packaging, modification and distribution of material from ER.
Lysosomes Membrane enclosed package of hydrolytic enzymes; involved in intracellular digestion; aid in renewal of cell’s own components by breaking them down. Vacuoles Membrane enclosed sacs; can fuse with a lysosome to digest their contents; vacuoles in protists pump excess water out; vacuole functions as a storage place in plants. Mitochondria Powerhouse of the cell; produces ATP through aerobic respiration; surrounded by a phospholipid bilayer; contain own circular chromosome and ribosomes like prokaryotes; believed to have been early prokaryotic cells that developed a symbiotic relationship with the ancestors of eukaryotes.
2.
nucleus lysosome
Organelles Cell membrane Composed of phospholipid bilayer with embedded proteins having both hydrophobic and hydrophilic regions; encloses cell and is selectively permeable (regulates what goes in and out of cell). Nucleus
nucleolus
Golgi apparatus
FOUNDATION REVIEW
Transport
What organelles are involved in packaging synthesized proteins for storage or for export out of the cell? The Golgi apparatus
3.
MCAT: BIOLOGY
CELLULAR RESPIRATION
denotes carbon-bearing molecules consumed/produced during respiration denotes molecules that contribute to the final NADH-FADH2 total
Glucose (6C) 2 ATP, 4 ADP 2 NAD+, 2 Pi
2 Pyruvate (3C) 2 ADP, 4 ATP 2 NADH 2 H+, 2 H2O
GLYCOLYSIS
2 ATP
Aerobic?
NO
NO
YES
Anaerobic
You are here.
You are here.
Pyruvate (3C) NADH
Ethanol (2C) (yeast) + CO2
FERMENTATION
Lactic Acid (3C) (muscle cells) NAD+
H+ You are here.
–2 ATP 2 Pyruvate (3C) 2 Coenzyme A 2 NAD+
PYRUVATE DECARBOXYLATION
2 Acetyl CoA (2C) 2 CO2 2 NADH
transport of high-energy electrons from cytoplasmic NADH across the NADH-impermeable mitochondrial membrane (1 ATP/NADH)
Aerobic
You are here.
2 Acetyl CoA (2C) 6 NAD+, 2 FAD 2 ADP, 4 H2O, 2 Pi
CITRIC ACID CYCLE
4 CO2 6 NADH 2 FADH2 2 ATP*, 4 H+, 2 Coenzyme A
2 ATP
You are here.
10 NADH total 2 FADH2 34 ADP 34 P i 10 H+, 5 O2
ELECTRON TRANSPORT CHAIN/ OXIDATIVE PHOSPHORYLATION
10 NAD+ 2 FAD 34 ATP (3 ATP/NADH, 2 ATP/FADH2) 10 H2O
+ 34 ATP 36 ATP
* 2 GTP are the direct products of the citric acid cycle. The 2 GTP subsequently donate their phosphate to 2 ADP to form 2 ATP and regenerate the original 2 GDP.
4.
FOUNDATION REVIEW
ENZYMES Enzyme Properties Accelerate the rate of a chemical reaction by decreasing the amount of activation energy necessary for the chemical reaction to proceed Enzymes catalyze and therefore accelerate the rate of chemical reactions by lowering the amount of activation energy necessary for these reactions to proceed. Reactions can take place without enzymes, but they would be much slower. Enzymes are neither changed nor consumed during a chemical reaction. Some enzymes are inactive and need to be activated. Example: pepsinogen → pepsin (activated by HCl) (inactive) (active) Enzyme specificity An enzyme will only catalyze one specific reaction (known as enzyme specificity). Molecules upon which an enzyme acts are called substrates and the substrate binds to the active site on the enzyme Potential energy
transition state E1 E2
E1 = activation energy of (forward) uncatalyzed reaction E2 = activation energy of (forward) catalyzed reaction
∆H
Reaction coordinate
Factors that affect enzymes There are several factors that may affect enzymes including: pH, concentration of substrate and enzyme, temperature, and cofactors.
Temperature Rates of enzyme-catalyzed reactions will increase as temperature increases, but only up to their optimum temperature. At higher temperatures, enzymes are denatured, which means that their 3-D structure is destroyed and they no longer work. pH Each enzyme also has an optimum pH (optimum pH for most human enzymes = 7.2). Above or below this optimum pH, enzyme activity declines.
5.
MCAT: BIOLOGY
rate of reaction
Concentration of substrate and enzyme If the concentration of enzyme is limited, then even if substrate concentration increases, the rate of the reaction will level off because there is no more enzyme available to bind with the substrate.
concentration of substrate
Cofactors/Coenzymes Many enzymes require nonprotein molecules to become active. These are called cofactors or coenzymes (e.g. vitamins).
6.
MCAT: BIOLOGY
Mitosis/Meiosis Humans have a total of 23 chromosome pairs (46 total). T he chromosome is a large structure which contains smaller structures called genes which code for all our traits. Humans have a t ot al of 23 chromos ome pairs (46 t ot al), one chromos ome in each pair from mom and one from dad in all s omat ic cells (body cells ) and 23 chromos omes in t heir gamet es (gamet es are in t he ovary and t es t es ). Haploid vs. Diploid
Mitosis Interphase/Cell Cycle G 1, S , G 2 are all part of int erphas e: G 1 and G (doubles cyt oplas m and organelles ); S (s ynt hes is, replicat ion of DNA, DNA goes from s ingle s t randed t o double s t randed, DNA s t ill in form of chromat in).
P
M
A
T
I nt
G2
er
ase
M
G 0 -no further division (nerves, muscles)
G1
ph S
C ell C ycle
S phase ÒS ynt hes is Óphas e: each chromos ome is replicat ed.
Homologous pair A
Homologous pair A
a
a
DNA duplicates B
b
4 chromosomes
B
b
Sister chromatids (identical)
Prophase Chromat in condens es int o chromos omes, s pindle apparat us forms, nucleoli and nuclear membrane dis appear Metaphase Chromos omes line up s ingle file on t he equat orial plane and each one at t aches t o a s eparat e s pindle fiber by it s kinet ochore. Anaphase S is t er chromat ids s eparat e and migrat e t o t he poles. Telophase Two cells are formed; a nuclear membrane is formed around bot h nuclei; cyt okines is (divis ion of t he cyt oplas m) occurs ; t wo ident ical, diploid cells wit h s ingle s t randed chromos omes are formed.
7.
FOUNDATION REVIEW
Meiosis Interphase I S ame as in mit os is ; s t art wit h a diploid cell; double-s t randed chromos omes Prophase I
Chromat in condens es int o chromos omes ; t he s pindle apparat us forms, and t he nucleoli and nuclear membrane dis appear; homologous chromos omes come t oget her and overlap (s ynaps is ); s ince each chromos ome cons is t s of 2 s is t er chromos omes, t his is called a t et rad (4 chromat ids ); homologous chromos omes exchange genet ic mat erial (genet ic recombinat ion/cros s ing over); part where chromos omes are joined is called t he chias mat a; genet ic recombinat ion promot es variat ion, t herefore daught er cells are not ident ical t o parent s.
Metaphase I Homologous pairs line up along t he equat orial plat e, and at t ach t o s pindle fibers. Anaphase I Homologous chromos omes are s eparat ed, and move t o oppos it e poles ; t his is called dis junct ion. If t hes e chromos ome pairs fail t o s eparat e, it is called nondis junct ion, and produces gamet es wit h one ext ra chromos ome (t ris omy) or one les s chromos ome (monos omy). Telophase I and Cytokinesis A nuclear membrane forms around each nucleus. Each chromos ome at t his point cons is t s of t wo s is t er chromat ids and a cent romere. Each cell has been reduced t o t he haploid condit ion. Meiosis II Analogous t o mit os is ; at t he end, t here will be 4 haploid cells which are different from parent cells, wit h s ingle s t randed chromos omes.
8.
MCAT: BIOLOGY
Oogenesis and Spermatogenesis Ovum (n)
Oogenesis
A
Secondary Oocyte A
Oogonium (2n) A
b
Primary Oocyte Meiosis II A
a
b
a
A
Meiosis I B
B
b
b
b
a
Second Polar Body
B
First Polar Body
A b
A
Spermatogenesis
Meiosis II b
A
A
A
a
b
a
Meiosis I B
B
b
Spermatogonium (2n)
b
a
Primary Spermatocyte
a B
Meiosis II B
a
Secondary Spermatocytes B
Sperm Cells (n)
Chromosomal abnormalities If the chromosomes fail to separate during anaphase of either meiosis I or meiosis II (nondisjunction), a chromosomal abnormality will occur. Typically, either a trisomy for a single chromosome or monosomy for a single chromosome will occur. Examples include: Down Syndrome (trisomy 21); Turner’s Syndrome (45 X); Kleinfelter’s Syndrome (XXY); trisomy 18. Only a few chromosomal abnormalities will produce viable offspring.
9.
FOUNDATION REVIEW
EMBRYOLOGY Fertilization
Fertilization usually takes place in the fallopian tube.
Occurs when the sperm and egg come together in the oviduct to produce a zygote (diploid-2n).
Fertilization
Zygote cleavage Morula (solid ball of cells)
Blastula (hollow ball of cells) gastrulation
Gastrula (3 cell layers: trilaminar)
implantation occurs in uterus Ectoderm
nervous system (brain and spinal cord), epidermis, lens of eye, inner ear
Endoderm
epithelial lining of disgestive tract, lungs, liver, pancreas
Mesoderm
muscles, skeleton, circulatory system, gonads, kidneys
neurulation Neurula
What parts might be malformed if the mesoderm develops incorrectly? Muscles, skeleton, circulatory system, gonads, kidneys 10.
MCAT: BIOLOGY
Structure and life activities of the fetus
Placenta Site of exchage of food, oxygen, waste, and water between the fetus and mother.
Amnion Provides watery environment, prevents shock to embryo/fetus.
Umbilical Cord Attaches embryo to placenta.
Chorion Membrane that surrounds the amnion.
Fetal Circulation Blood is oxygenated in the placenta. The blood is shunted away from the developing lungs and liver by the ductus venosus, ductus arteriosus, and the foramen ovale.
Fetal Respiration Fetus receives oxygen and disposes of carbon dioxide at the placenta. This is facilitated by fetal hemoglobin, which has a higher affinity for oxygen than does maternal hemoglobin.
What shunts blood away from the lungs in the fetus? The ductus venosus shunts blood away from the pulmonary circulation. What is the function of the placenta? The placenta is the site of O2 and CO2 exchange between the fetus and mother.
11.
FOUNDATION REVIEW
CLASSICAL GENETICS Definitions
Allele One of a pair of genes
Dominant The trait that is expressed even when combined with other alleles.
Recessive There must be two recessive alleles present in order for this trait to be expressed.
Homozygous A homozygous individual is genetically pure for a given trait, that is, that this individual possesses two identical alleles (TT, tt).
Heterozygous A heterozygous individual has two different alleles for a given trait (Tt).
Phenotype Outward appearance of an individual with respect to a given trait (an organism with a TT or Tt genotype organism is tall; tall is the phenotype).
Genotype The genetic characteristics of an individual with respect to a given trait (Tt).
12.
MCAT: BIOLOGY
Monohybrid and dihybrid crosses/Punnett Square
Cystic fibrosis is an autosomal recessive disorder. If a male with cystic fibrosis marries a female who is a carrier of cystic fibrosis, what is the chance they will have a child with cystic fibrosis?
r
r
R
Rr
Rr
r
rr
rr
Looking at the Punnett square, 50% of the offspring are Rr and phenotypically normal, while the other 50% are rr and have cystic fibrosis. There is a 50% chance they will have a child with cystic fibrosis.
Sex determination Females (XX) and males (XY)
Mendel’s Laws The Law of Dominance If two individuals with contrasting, pure-breeding traits are crossed, the trait that is expressed phenotypically in the offspring is the dominant trait. The trait that remains hidden is recessive. The Law of Segregation Every normal diploid organism has two alleles for each inherited trait (one from the maternal parent and one from the paternal parent). During meiosis, these alleles segregate, forming gametes that carry only one allele for a given trait. As a result, in a monohybrid cross between two heterozygotes, the phenotypic ratio of the offspring is 3 (dominant): 1 (recessive). The Law of Independent Assortment During meiosis, all allelic combinations are distributed to gametes with an equal probability, and the distribution of one pair has no effect on the distribution of another pair (if the genes are unlinked). Thus, in a dihybrid cross for unlinked traits 1 and 2, the phenotypic ratio of the offspring is 9 (dominant for both traits): 3 (dominant for 1 trait, recessive for trait 2): 3 (recessive for trait 1, dominant for trait 2): 1 (recessive for both traits).
13.
FOUNDATION REVIEW
Pedigrees/Types of Inheritance Autosomal recessive inheritance If autosomal, there will usually be both males and females affected. (However, since one family is such a small sample size, the sex ratio of affected individuals may not be equal.) If it skips a generation, it is recessive. Rr
Rr Key:
= normal male = normal female = affected male
rr
Rr
rr
rr
rr
RR or Rr
RR or Rr
= affected female
Rr
Autosomal dominant inheritance If autosomal, there will usually be both males and females affected. (However, since one family is such a small sample size, the sex ratio of affected individuals may not be equal.) In general, if it doesn’t skip generations, it is dominant. Rr
rr Key:
= normal male = normal female = affected male
Rr
rr
Rr
Rr
Rr
rr
rr
= affected female
Rr
14.
MCAT: BIOLOGY
X-linked or sex-linked recessive inheritance If X-linked, there will usually be more affected males than females. (However, since one family is such a small sample size, this may not be true for a single family.) No male-male transmission. XRY
XRXr
Key:
= normal male = normal female = affected male
r
XY
r
R R
XY X X or XRXr
r
R R
R
XY X X X Y or XRXr
= affected female
XRXr XRXr
Blood types (Example of codominance and multiple alleles)
15.
Anti-B antibody; A antigen
A and AB
A and O
Anti-A antibody; B antigen
B and AB
B and O
No antibodies; A and B antigens
AB
A, B, AB, O
Anti-A and anti-B antibodies; no antigens
A, B, AB, O
O
MCAT: BIOLOGY
MICROBIOLOGY
Viruses nucleic acid and protein; lytic vs. lysogenic Viruses infect cells, take over the host’s cellular machinery and direct the replication of the viral genome and protein coat. Viruses may be lytic (causing the cell to disintegrate) or lysogenic (remaining dormant in the cell). They contain either DNA or RNA and some essential enzymes surrounded by a protein coat (capsid). Viruses that exclusively infect bacteria are termed bacteriophages.
Bacteria prokaryotic, single-celled, lack true nuclei, and contain 1 double-stranded circular chromosome; no nuclear membrane; have cell wall Almost all forms have cell walls (made of peptidoglycan). Nutrition heterotrophic, saprophytic, or autotrophic Can be obligate aerobes, facultative anaerobes, or obligate anaerobes. Shape bacilli, spirilli, cocci Bacteria are classified by their morphological appearance: cocci (round), bacilli (rods), and spirilli (spiral). Some forms are duplexes (diplococci), clusters (staphylococci), or chains (streptococci). Reproduction binary fission Bacteria reproduce by binary fission.
Fungi eukaryotic; most are multicellular; heterotrophic, absorptive nutrition (either saprophytic or parasitic); decomposers; yeasts reproduce by budding; fungi by sporulation Eukaryotic; most are multicellular Heterotrophic, absorptive nutrition (either saprophytic or parasitic); decomposers Examples include yeasts, molds, and mushrooms. The basic body of the fungi is a netlike mass of filaments called hyphae. Many hyphae make up a mycelium. Fungi reproduce via spores (either produced sexually or asexually). Yeasts reproduce via budding. 16.
