mcat biology notes 3.pdf

7/22/2019 MCAT Biology Notes 3.pdf

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MCAT BIOLOGY – Muscular and Skeletal Systems

V. MUSCLE AND SKELETAL SYSTEMS

a. Skeletal Muscle

i. voluntary movement with somatic innervation

ii. cells arranged into fibers, cells are multinucleated

iii. sarcomere – contractile, functional unit of the muscle cell; very regulararrangement gives skeletal muscle its striated appearance

iv. sarcoplasmic reticulum – variation of the smooth endoplasmic reticulum

v. stores calcium for release during contraction

vi. sarcoplasm – cytoplasm of muscle cells

vii. sarcolemma – plasma membrane of muscle cells

viii.Red fibers

1. slow twitch fibers with increased numbers of mitochondria and increased

myoglobin content (myoglobin is similar to hemoglobin, but only has one

subunit, it stores oxygen for release when it is needed during cellular

respiration)2. able to perform aerobic respiration for long periods of time – used during

sustained, vigorous activity (long-distance running)

ix. White fibers

1. fast twitch fibers that have decreased numbers of mitochondria and low

myoglobin content

2. Lots of anaerobic respiration, have

increased rate of contraction, but are fast

fatigueable – sprinting

b. Smooth Muscle

i. intestines, blood vessels, bladder, uterusii. mononucleated

iii. non-striated, but still contains actin and myosin

iv. contractions are slower but maintained longer

v. have myogenic activity

vi. reflexive contraction, independent of nervous

innervation

c. Cardiac Muscle

i. striated with one or two nuclei per cell

ii. autonomic nervous system modulates cardiac

activity, but it also has myogenic activity – heart

will continue to beat if all nervous connections

are severed, it will just not be able to increase

or decrease its rate in response to exercise/rest

d. Muscle Contraction

i. Initiation

1. stimulated by a motor neuron at the

neuromuscular junction

2. acetylcholine is released! binds to



receptors on sarcolemma! if enough

are bound, an action potential is

potentiated

ii. Contraction

1. Action potential enters t-tubules!

calcium released from the sarcoplasmic

reticulum2. Calcium binds to troponin! troponin

moves tropomyosin off actin binding sites

3. Myosin heads bind to actin and pull on them

to contract the sarcomere

4. I-zone and the H-zone reduce in size as the

Z-lines come together

iii. Relaxation – calcium is pumped back into

sacroplasmic reticulum

1. rigor mortis occurs when no ATP is left to

move calcium back into SR! tonic

contraction

**stimulus for contraction is all-or-none for individual fibers (they either

contract or they don’t), but the activation of progressively increasing

numbers of fibers allows a graded response in the entire muscle (you can

move your arm a little bit or contract it all the way)



I. Skeletal System

a. Joints

i. immovable – skull

ii. movable

1. synovial capsules – enclose joint cavity

2. synovial fluid, fills capsule, lubricates joint

3. articular cartilage – smooth, surrounds joints to reduce tension duringmovement

4. ligaments – connect bone to bone

5. tendons – connect bone to muscle

b. Skeleton

i. Axial – skull, vertebral column, ribcage

ii. Appendicular – limbs and pelvic bones

c. Cartilage

i. chondroitin sulfate and collagen matrix – both released by chondrocytes

ii. external ear, nose, walls of larynx, trachea, skeletal joints

iii. mostly avascular

iv. Types

1. Hyaline

a. Most common, in joints, ends of long bones

2. Fibrocartilage – intervertebral discs

3. Elastic – all other locations

d. Bone

i. compact bone – dense bone creates exterior of bones

ii. spongy bone – creates medullary cavity inside large bones

iii. trabeculae – bony spicules that create a bony network inside compact bone

iv. cavities between trabeculae have yellow or red bone marrow

1. Yellow marrow – inactive, infiltrated by adipose tissue

2. Red marrow – responsible for blood cell formation

v. Bone structure

1. organic components – proteins: collagen and glycoproteins

2. inorganic – calcium, phosphate, hydroxide

3. hydroxyapatite crystals – mineral salts made of calcium and phosphorus

4. Osteon – structural unit of bone

5. Haversian canals – contain blood vessels, nerve fibers, lymph ducts

6. Lacunae – spaces that contain mature bone cells – osteocytes

7. Canaliculi – small canals for exchange of nutrients and wastes

8. Osteoblasts – bone builders – from calcium in bloodstream9. Osteoclasts – breakdown bone – release calcium to bloodstream

vi. Types of Bone Formation

1. Endochondral ossification

2. Existing cartilage is replaced by bone

3. Long bones – growth plates in children

4. Intramembranous ossification

a. Mesenchymal tissue (undifferentiated embryonic tissue) is

transformed into and replaced by bone



b. Skull in infants

vii. Types of bones

1. Long – femur, phalanges, metatarsals, metacarpals

2. Short – wrist, patella

3. Flat – cranium, sternum, scapula

4. Irregular – vertebrae, pelvis



MCAT BIOLOGY - Respiratory and Skin Systems

I. RESPIRATORY AND SKIN SYSTEMS

a. Respiratory System

b. Path of Air:

i. External nares! nasal cavities/sinuses (air filtered and warmed)! pharynx!

larynx! trachea! 2 bronchi! bronchioles! alveoli (small air sacs for gas

exchange – 300 million per lung)

ii. Surfactant – produced by alveolar type II cells – decrease surface tension so that

alveoli can expand; not produced by fetus until just before birth – decreases ability

of premature infant to breathe

iii. Ventilation

1. inhalation

a. diaphragm contracts and flattens

b. external intercostal muscles contract – lifts ribcage/chest wall up and

out

c. interpleural pressure decreases! volume of lungs increases!

lungs fill with air due to negative pressure (air drawn in by vacuum)

2. expiration

a. passive process due to elasticity of chest wall and lungs



b. thoracic cavity decreases in size

and air is expelled

c. with forced expiration, internal

intercostals contract, pull ribcage

down

3. Medulla Oblongata

a. Controls breathing based onoxygen status/carbon dioxide

status of blood

b. Can be overridden so that person

consciously controls breathing

4. Hemoglobin Curve - see figure

(remember cooperative regulation?)

II. Skin – part of the integumentary system that includes skin,

hair, nails, surface glands, some nerve endings (sebaceous

glands secrete oil, sudoriferous glands secrete sweat)

a. Functions

i. homeostasis, osmoregulation

ii. thermoregulation

iii. physical protection

b. Structure

i. Epidermis – keratinized stratified squamous epithelium (5 layers - CLGSB)

1. deepest layers contain Merkel cells (nerve endings) and melanocytes

(pigment-producing cells stimulated by sun exposure)

2. Langerhans cells – macrophages that patrol skin for bacteria, engulf debris

3. Surface is covered with dead, keratin-filled cells

ii. Dermis

1. 2 Layers

a. Papillary layer

i. Most superficial 20%

ii. Contains dermal papillae with extend into the epidermis and

provide more

surface area for

connection of

the two layers

b. Reticular layer

i. Dense irregular

connectivetissue

ii. Mainly reticular

(collagen)

fibers

iii. Hypodermis (subcutaneous layer)

1. Connective tissue

2. Adipose

3. Blood vessels, etc



MCAT BIOLOGY – Reproductive System and Development

I. REPRODUCTIVE SYSTEM AND DEVELOPMENT

i. It’s most important to know

the differences betweenmitosis and meiosis and to

keep track of how many chromatids, homologous pairs, etc., are present at each

stage.

b. Prior to meiosis, the cell undergoes a round of DNA replication, resulting in 92 chromatids

(but the cell remains 2n, b/c there are still only chromosomes from 2 parents, they’ve just

been replicated)

c. Meiosis I

i. Prophase I

1. The homologous chromosomes find one another and align (ie, the maternal

chromosome 21 and the paternal chromosome 21 match up)2. Crossing over occurs between the maternal and paternal chromosomes so

that some of the maternal genetic information winds up on the paternal

chromosome and vice versa. This is another way to increase genetic

diversity.

ii. Metaphase I

1. Homologous pairs move to the metaphase plate

iii. Anaphase I



1. Homologous pairs separate – this is different from mitosis because in

mitosis, the sister chromatids separate – know the difference!

iv. Telophase I

1. The two cells divide and the homologous chromosomes are now separate,

but the sister chromatids remained joined together.

2. The cells are now 1n b/c the maternal and paternal chromosomes have

separated. There are now 46 chromatids joined together in 23chromosomes.

d. Meiosis II

i. Meiosis II is exactly like mitosis in that the chromosomes align at the metaphase

plate and then separate. The only difference is that there are only 23 chromosomes

at the start of meiosis II instead of the 46 present at the beginning of mitosis.

ii. At the end of meiosis II, there are 23 chromosomes and the cell is 1n.

e. Gametogenesis

iv. Male Reproduction

1. Path of Sperm

a. Testes! Epididymis (sperm maturation completes and sperm are

stored here)! vas deferens! seminal vesicles add fluid!

prostate adds fluid! bulbourethral (Cowper’s) glands add fluid!

penile urethra! vagina (sperm become activated – “capacitation”

2. Spermatogenesis



a. Spermatogonia go through episodes of mitosis and differentiation to

increase in number, they become Primary Spermatocytes (46

chromosomes, 2n)

b. Primary Spermatocytes go through one round of meiosis and

become Secondary Spermatocytes (23 chromosomes, 1n).

c. Secondary Spermatocytes go through meiosis II to become

Spermatids (23, 1n)d. Spermatids go through a process known as spermeogenesis in which

their cytoplasm is reduced, the DNA is tightly packed, and the cell

grows a flagellum to become a sperm.

3. Anatomy of Sperm

a. Head – contains DNA

b. Acrosome – covers top of

head – contains enzymes

for dissolving through the

outside of the egg

c. Neck – contains

mitochondria

d. Tail/Flagellum -

movement

2. Testicular Cells

a. Leydig Cells - produce

testosterone when

stimulated by luteinizing

hormone

b.Sertoli Cells

c.Support sperm

development by providing

nutrients, removing

waste, and keeping the

sperm separate from the body’s immune system (the blood-testes

barrier).

v. Female Reproduction

1. Oogenesis

a. Oogonia form during the development of the female fetus (they are2n). There are approximately 5 million oogonia present before the

female fetus is born.

b. The oogonia go through differentiation to become Primary Oocytes.

Many degenerate so that all the oogonia only result in 1 million

primary oocytes.

c. The primary oocytes go through a round of replication and enter

meiosis I, but become arrested in Prophase I during crossing over.



d. The primary oocytes become surrounded by follicular cells and

become a Primordial Follicle. This process begins after birth and

continues until puberty at which time there are 40,000 primordial

follicles.

e. At the start of a menstrual cycle, 10-20 primordial follicles become

activated and complete meiosis I to become Secondary Oocytes.

f. The secondary oocytes are supported by the follicular cells whichinclude:

i. Granulosa cells which surround the oocyte. They convert

androgen into estradiol (a form of estrogen).

ii. Thecal cells surround the granulosa cell layer and produce

androgens.

iii. The estradiol ensures the survival of the oocyte and allows it

to continue maturing (the other oocytes that started to

develop at the beginning of the cycle degenerate).

g. At ovulation, the oocyte and a few of the surrounding follicular cells

are extruded from the ovary.

h. The remaining follicular cells remain behind in the ovary, become

known as the corpus luteum and continue producing estradiol and

progesterone.

2. Menstrual Cycle

a. Day 1 – Menses begins (uterine lining from the previous cycle is

shed)

b. Day 5 (or whenever menses ends) - ovary enters the Follicular

Phase – follicles begin developing

i. Follicle Stimulating Hormone (FSH) secreted from the

anterior pituitary stimulates development of the follicles



ii. Luteinizing Hormone (LH), also from the anterior pituitary,

stimulates the thecal cells to convert androgens to estradiol.

iii. Uterus lining begins to regrow

1. Estrodiol from the follicles stimulates the lining to

grow.

iv. Day 14 – Ovulation

1. The estradiol and LH enter into a positive feedback

loop so that increasing LH causes increasingestradiol, which increases LH and so on. Eventually

an “LH Surge” causes ovulation.

v. Day 14-28

1. The ovary enters the Luteal Phase (because it now

contains the corpus luteum that was left behind after

ovulation).

2. The corpus luteum secretes progesterone that

maintains the uterine lining.



3. The enters its secretory phase and the uterine lining

becomes ready to accept a fertilized egg.

4. Estrogen continues to prepare the lining.

5. If no fertilization occurs, the corpus luteum

degenerates, progesterone decreases and the uterine

lining begins to slough, heralding the start of a

menses and Day 1 of the subsequent cycle.6. If fertilization and implantation occur – the

developing embryo begins to secrete beta-HCG

which maintains the corpus luteum, so that it

continues to secrete progesterone, which maintains

the uterine lining. Eventually, the placenta begins to

secrete its own progesterone.

3. Menopause occurs when ovaries become depleted of primordial follicles –

the pituitary sends the hormones (FSH and LH), but no follicles are present

to begin producing estradiol.

vi. Developmental Mechanisms

1. Cell Specialization

a. Determination

i. Progressive restriction of a cell’s developmental potential

ii. As embryonic cells develop more and more, they are more

restricted as to what types of cells they can become

b. Differentiation

i. Structural and functional divergence of cells as they become

specialized during development

ii. Dependent on the control of gene function – the genes that

are activated determine the type of cell that will develop

c. Induction

i. Ability of one group of cells to influence the development of

an adjacent group of cells.

1. ie, as the ureters grow out from the bladder, they

induce surrounding cells to develop into the kidneys



MCAT BIOLOGY - GENETICS

I. Genetics

a. Mendelian Concepts and Their Application

i. Mendel’s Four Theories

1. Alternative versions of genes (alleles) account for variations in inherited

characteristics2. For each character, an organism inherits 2 alleles, one from each parent

3. If the two alleles differ, then one, the dominant allele, is fully expressed in

the organism’s appearance; the other allele, the recessive allele, has no

noticeable affect on the organisms appearance

4. The two alleles for each characteristic segregate during gamete production• “Mendel’s Law of Segregation”

b. Other Important Mendelian Concepts

i. Law of Independent Assortment

1. the segregation of the members of any pair of alleles is independent of the

segregation of other pairs in the formation of reproductive cells when thealleles are located on different chromosomes

• in other words, the alleles on different chromosomes segregate

independently

ii. Test Cross

1. Reveals the genetic makeup of the offspring of parents that exhibit

dominant traits

2. Dihybrid Cross• Mating of parents with 2 sets of differing characteristics of interest• A dihybrid cross looks at the genetic makeup of the F2 generation



• When performing a dihybrid cross, it is crucial that the correct

gametes be identified from each parent• If crossing a homozygous dominant parent with a parent that is

homozygous recessive for two traits, the F2 generation will have a

9:3:3:1 phenotypic ratio

i. Nine will have both dominant phenotypes

ii. Three will have one dominant phenotype and three will havethe other dominant phenotype

iii. One will be recessive for both traits

c. Genetics concepts and vocabulary

i. Locus – a particular place along the length of a certain chromosome where a given

gene is located

ii. Genotype – the genetic makeup of an individual

iii. Phenotype – organism’s appearance (a manifestation of its genotype)

iv. Homozygous – organism has a pair of identical alleles at a given locus

v. Heterozygous – organism has two different alleles for a given character

d. Rules of Probability

i. Multiplication Rule

1. computing the chance of two independent events occurring simultaneously

2. for example – computing the chance that 2 coins will land heads up when

they are flipped:

! x ! = "

**chance of getting heads with one coin is one out of two,

multiply for two coins

3. Similarly, what is the probability that an offspring will have white flowers

(homozygous recessive) if both parents are heterozygous:

! x ! = "

**same probability as coin – one half chance that each

parent will give a recessive allele

4. Can also be used for F2 crosses:• If two heterozygotes are crosses (YyRr), what is the probability of

getting a homozygous dominant (YYRR) offspring?

! x ! x ! x ! = 1/16

**one half chance of getting a dominant allele at each locus

ii. Addition Rule

1. the probability of an event that can occur in two or more different ways is

the sum of the separate probabilities of those ways

• what is the probability of getting a heterozygous offspring whencrossing two heterozygous parents?

" + " = !

**there is a one in four chance that the dominant allele will come

from the mother and the recessive allele will come from the father;

there is a one in four chance that the dominant allele will come from

the mother and the recessive allele will come from the father. These

are two separate ways to get the same outcome, so the probabilities

are added.



e. Complications – Why Mendel’s Four Rules Don’t Always Hold

i. Codominance – a phenotypic situation in which both alleles are expressed in the

heterozygote, but not blended (ABO blood groups)

ii. Incomplete dominance – a type of inheritance in which the F1 hybrids have an

appearance that is intermediate between the phenotypes of the parental varieties

1. pink flowers in the offspring of red and white homozygous parents

iii. Linkage – genes located near one another on the same chromosome don’texperience independent assortment (because they will segregate together on the

chromosome)

iv. Pleiotropism – alteration of a single gene that appears to affect apparently unrelated

phenotypes

v. X-inactivation – during embryonic development, one x-chromosome in each cell in

females becomes inactivated and is then known as a Barr body

1. all the cells that are derived from those cells will then only express the x-

chromosome that was not inactivated. As a result female animals are

mosaics, with different portions of their bodies expressing one or the other

x-chromosome

vi. Polygenism – complex trait that is influenced by multiple genes (height)

vii. Penetrance – likelihood that a given genotype will result in the expression of the

expected phenotype

viii.Epistasis – expression of one gene is completely dependent on the expression of

another gene (ie, transcription factors)

ix. Non-disjunction – failure of chromosomes to separate correctly during meiosis

(results in an offspring with an extra chromosome

1. usually not compatible with life, however, having three copies of

chromosome 21 is compatible with life – trisomy 21 is known as Down

Syndrome

x. Sex-linked genes – genes are located on a sex chromosome

1. this affects probabilities, dominance, etc.

Example Probability Question:

Hemophilia is an X-Linked recessive disease. A woman does not have hemophilia, but her father

does. She marries a man with hemophilia. What is the probability that their first child will be a son with

hemophilia?

**Use multiplication rule because we need to calculate the probability of two separate events. !

chance of having a son. ! chance that the son (who has the sex chromosomes XY) will get an X with thehemophilia gene from his mom (she can either give an X with hemophilia or an X without hemophilia

(because she is a carrier):

! x ! = "

II. Hardy-Weinberg Equilibrium

a. allele and genotype frequencies in a population remain constant (are in equilibrium) from

unless disturbed

b. Five Conditions:



i. Very large population size

ii. Isolation from other populations

iii. No net mutations

iv. Random mating

v. No natural selection

c. If any of the five conditions are altered, the population will experience evolution

i. Remember that populations are always evolvingd. Hypothetical populations that fit the H-W conditions can be analyzed with the following

equations:

p + q = 1

where p = frequency of the dominant allele and q = frequency of the

recessive allele

p2 + 2pq + q2 = 1

where p2 = frequency of homozygous dominant individuals, 2pq =

frequency of heterozygotes and q2 = frequency of homozygous recessive

individuals

III. Evolution

a. Natural Selection

i. Fitness – the relative contribution an individual makes to the gene pool of the next

generation

1. a female who contributes one adult to the next generation as a fitness of 1.0

b. Speciation

i. Remember the mnemonic – King Philip Came Over For Good Soup

ii. Kingdom! Phylum! Class! Order! Family! Genus!

Species

c. Comparative Anatomy

i. Four Chordate Features (all chordates have these characteristics at

some point in their development)

1. Notochord – becomes the vertebral column

2. Dorsal, hollow nerve cord – becomes the CNS

3. Pharyngeal Slits – become pharynx or gills as well as other

head and neck structures

4. Muscular, post-anal tail – may or may not be present in fully

formed animals

mcat biology notes 3.pdf

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