Fundamentals of Biology - Exam 4

Chapters; 17, 51, 42, and 45. God be with me.

Different forms of a gene are called:

Alleles (Alleles = Alternatives)

A cross between two parents that differ by a single trait is a ___cross.

Monohybrid

Crossing round-seeded pea plants with wrinkled-seeded pea plants result in progeny that all has round seeds. This indicates that the wrinkled-seeded trait is?

Recessive

The physical appearance of a character is the ___ whereas the genetic constitution is the ___.

Physical = Phenotype, Genetic = Genotype

It has been found that a certain locus of the human genome, 200 different alleles exist in the population. Each person has at most ___ alleles.

Two. Humans are diploid organisms meaning each person can only inherit one allele for a gene from each parent, two in total.

Cleft chin is an X-linked dominant trait. A man with a cleft chin marries a women with a round chin. What percentage of their female progeny will show the cleft chin trait?

100% of their female offspring will have a cleft chin. This is because the father only has one X to pass on, the cleft-dominant, cleft-presenting X.

Cleft chin is an X-linked dominant trait. A man with a cleft chin marries a women with a round chin. What percentage of their male progeny will show the cleft chin trait?

0% of their male offspring will have a cleft chin. This is because the father is the only parent carrying the cleft gene but he passes on the unaffected Y. Male offsprings will only receive unaffected X chromosomes from their mother. Therefore they will not have a cleft-chin.

Separation of the alleles of a single gene into different gametes is called?

Segregation

In ABO blood type system…

A and B are codominant, both are dominant over O

The sharp peak of estradiol during the ovarian cycle:

Stimulates secretion of LH and ovulation

How many spermatids generated from one secondary spermatocyte?

Two spermatids (4 total spermatid, each developing into a mature sperm cell)

How many secondary oocytes are generated from one primary oocyte?

one secondary oocyte

Name the three phases of the ovarian cycle;

Follicular: Follicles mature and produce estrogen, dominant follicle releases an egg

Ovulation: Mature egg is released from ovary into the fallopian tube, usually triggered by LH

Luteal: The ruptured follicle transforms into the corpus luteum, produces progesterone and estrogen. Unless pregnant the corpus luteum degenerates

Name the phases of the uterine cycle;

Menstrual: Shedding the uterine lining (endometrium) during the menstrual cycle.

Proliferative: Uterine lining begins to thicken to prepare for potential pregnancy.

Secretory: The lining thickens and becomes more sensitive to fertilization.

Which ion is responsible for voltage rising in membrane potential?

The rising phase of membrane potential (depolarization) is caused by the influx of sodium ions (Na+) into the cell.

When a stimulus reaches threshold, voltage-gated sodium channels open, allowing positively charged sodium ions to rush into the cell, making the membrane potential less negative and more positive (rise).

Which ion is responsible for voltage falling in membrane potential?

The ion responsible for the falling phase (repolarization) of the membrane potential is primarily potassium (K+) ions.

When voltage-gated potassium channels open, potassium ions flow out of the cell, decreasing the membrane potential and returning it towards its resting state

What is the conformation of the vg-K+ and vg-Na+ channels at rest?

vg-Na+ are closed but capable of being opened (first step, before rise).

vg-K+ channels are closed (last step, phase after fall)

The thick filament is composed mostly of ____ molecules.

Myosin

During muscle contraction, cross-bridges form between____ and ___.

Myosin and Actin

Specifically, the globular heads of myosin bind to actin filaments, creating these cross-bridges.

Describe the steps that lead to a muscle contraction;

1. Nerve Impulse & Neuromuscular Junction:

• A nerve impulse (action potential) travels down a motor neuron to the neuromuscular junction, a synapse where the neuron connects with a muscle fiber. 

• At the junction, the motor neuron releases a neurotransmitter called acetylcholine (ACh). 

• ACh binds to receptors on the muscle cell membrane (sarcolemma), triggering a depolarization (rise) event. 

• This depolarization wave travels down the sarcolemma and into T-tubules. 

2. Release of Calcium:

• The electrical signal reaching the T-tubules stimulates the release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR), a specialized calcium storage organelle.

• This released Ca2+ diffuses into the sarcomere, the functional unit of muscle contraction. 

3. Cross-Bridge Cycling:

• Ca2+ binds to troponin, a protein on the actin filaments, causing it to change shape and expose myosin binding sites on the actin. 

• Myosin heads, which are part of thick filaments, can now bind to the exposed binding sites, forming cross-bridges. 

• The myosin head then undergoes a conformational change, pulling the actin filament towards the center of the sarcomere (the "power stroke"). 

• The myosin head then detaches from actin and uses ATP (energy) to recock and bind again, repeating the cycle. 

• This repeated binding, pulling, and detaching of myosin heads is known as the cross-bridge cycle, and it propels the thin filaments along the thick filaments. 

4. Sarcomere Shortening & Muscle Contraction:

• As the actin filaments are pulled towards the center of the sarcomere, the sarcomere shortens. 

• This shortening of individual sarcomeres throughout the muscle fiber leads to overall muscle contraction. 

• ATP is essential for the detachment and reattachment of myosin heads, allowing for repeated contractions. 

5. Relaxation:

• When the nerve impulse stops, Ca2+ is pumped back into the SR, reducing the amount of free Ca2+ in the cytoplasm. 

• With Ca2+ removed, troponin returns to its original shape, blocking the myosin binding sites on actin. 

• Myosin heads can no longer bind to actin, and the cross-bridges break. 

• The muscle relaxes as the thin filaments slide back to their original position. 

Ll codes for long eyelashes, which variable is the genotype?

Ll is the genotype

Ll codes for long eyelashes, which variable is the phenotype?

Long eyelashes is the phenotype

What is a dominant allele?

In a heterozygous individual, the allele that determines the phenotype

Heterozygous = Different (Dominant x Recessive)

Homozygous = Same (Dom. x Dom., Rec. x Rec.)

Pea plants cannot self-fertilize because an individual plant is either female or male, having either ovaries or stamens but not both.

False

They possess both male (stamen) and female (ovary) reproductive organs within the same flower, allowing for self-pollination where pollen from the stamen of a flower can fertilize the ovary of the same flower.

The probability of obtaining a dominant phenotype from self-fertilization of a heterozygous individual is:

75%

If a pink snapdragon is self-fertilized, the offspring are red, pink, or white. What type of inheritance pattern does flower color exhibit in this example?

Incomplete dominance

In codominance

the heterozygote exhibits the phenotypes of both parents equally

What is a testcross?

a cross between an organism of unknown genotype with a homozygous recessive individual.

The single-factor crosses performed by Mendel support the observation that…

the two alleles for a given gene are distributed randomly among an individual's gametes

The two-factor crosses performed by Mendel support the observation that…

alleles for a given trait are distributed randomly among an individual's gametes independent of the alleles for other traits.

Monohybrids

Parents differ by one trait

What unexpected discovery was made in generation 3 (F₂) of Mendel’s pea plants?

The revival of the recessive gene (dwarfism) not seen in generation 2 (F₁).

3:1 ratio of tall to dwarf (Dom:Rec presenting) plants

Mendel’s Law of Segregation

Two copies of a gene segregate from each other during the transmission from parent to offspring.

In a test cross if any offspring display recessive genes the parent must be?

Heterozygous

Two-factor cross

Dihybrid cross (follows two characters)

Ex. seed color AND seed shape

Law of Independent Assortment

Alleles of different genes assort independently of each other during gamete formation

Locus

The physical location of a gene on a chromosome

Linked genes

Genes located near each other on the same chromosome tend to be inherited together

Pedigree

Inherited trait is analyzed over the course of several generations in one family.

Ex. Cystic Fibrosis or Huntington’s Disease

Disease genes can be recessive or dominant, autosomal or sex-linked

Recessive (Both parents are carriers)

Dominant (One parent is a carrier)

Autosomal (Disease potential)

Sex-linked (Only effects one sex) (ex. color blindness)

X-linked recessive disorders are much more common in males than in females

For a recessive X-linked trait to be expressed a female needs two copies (homozygous) while a male only needs one copy (heterozygous)

Alleles can show different degrees of dominance

Incomplete Dominance / Codominance

In what order do sperm move through the structures of the female reproductive tract?

vagina; cervix; uterus; oviduct

Once an egg has been fertilized, what event is crucial for preventing additional sperm from inserting DNA into the egg?

the cortical reaction

a process in fertilization where an egg releases cortical granules, specialized vesicles, into the the space between the egg's plasma membrane and its outer layer (perivitelline space)

In female mammals, germ cells

are arrested in meiosis I until puberty

Fertilization of an ovum normally occurs in the

Oviduct (the tube through which an ovum or egg passes from an ovary.)

The outcome of cleavage during embryonic development is the production of a…

Blastula

A hollow sphere of cells, or blastomeres, produced during the development of an embryo by repeated cleavage of a fertilized egg. (Resembles frogspawn)

What are the three glands that produce the liquid portion of semen?

1. prostate

2. seminal vesicles

3. bulbourethral

Male reproductive tract in the proper order from sperm production to ejaculation

1. seminiferous tubules

2. epididymis

3. vas deferens

4. ejaculatory duct

5. urethra

Order of the three phases of the ovarian cycle

follicular; ovulation; luteal

The electrical difference across a neuronal membrane is measured in

millivolts

The ion that increases its intracellular concentration in order to trigger the release of neurotransmitters is

Ca ²⁺

The Role of Calcium:  Ca ²⁺ binds to the troponin complex on the thin filaments, initiating muscle fiber contraction

Saltatory conduction is a term applied to the "jumping" movement of action potentials

along myelinated axons

After an action potential is triggered, the rapid increase in membrane potential can be attributed to

the opening of voltage-gated sodium channels.

Identify the key feature of the action potential that ensures it will travel only one direction

the inactivation state of the voltage-gated Na ⁺ channel

The period following an action potential during which a neuron cannot be stimulated to generate another action potential is referred to as

the refractory period (returning to its factory stage)

Cells in the nervous system responsible for information processing?

Neurons

Cells in the nervous system responsible for providing mechanical and metabolic support

Glial cells

Synaptic vesicles discharge their contents by exocytosis at the…

presynaptic membrane

The level of depolarization at which an action potential will be triggered is referred to as the…

threshold potential

In a reflex arc, the correct sequence of cell types through which an electrical signal would pass would be

sensory neuron → interneuron in the CNS → motor neuron

Release of cross-bridges depends most directly on

ATP

For the hierarchy of skeletal muscle organization, which accurately lists the order of structures from "small" to "big"?

sarcomere; myofibril; muscle fiber; motor unit

In muscle function at the sarcomere level, the formation of cross-bridges is regulated by the binding of ___ ions to ____.

calcium; troponin

The primary reservoir for calcium that is released during excitation-contraction coupling in a skeletal muscle fiber is the…

sarcoplasmic reticulum

The acetylcholine receptor is a ligand-gated channel that produces

Depolarization by allowing Na ⁺ ions to enter the muscle fiber.

Muscle cells are stimulated by acetylcholine released from the terminals of

motor neuron axons

Parts of Neurons;

dendrites - highly branched extensions that receive signals from other neurons

cell body - most organelles reside

axon (single) - longer extension, transmits signals to other cells

axon hillock - cone-shaped base of an axon, where signals are generated

axon terminals – convey electrical or chemical message to other cells

The branched ends of axons transmit signals to other cells at a junction called the synapse

synaptic terminals - the part of each axon branch that forms a synapse

neurotransmitters - chemical messengers that pass information from the transmitting neuron to the receiving cell

Plasma membrane acts as a…

Barrier

Resting Potential

70 millivolts resting potential inside neurons

Interior more negative than exterior

Sufficient for generating action potential

Electrochemical gradient

Opposing forces of chemical and electrical gradients can create an equilibrium where there is NO net movement

Depolarization = Rise (Na⁺ v-gate opens)

Repolarization = Fall (K⁺ v-gate opens)

Most synapses are _______ , in which a _______ carries information from the presynaptic neuron to the postsynaptic cell

chemical synapses, neurotransmitter

Excitatory Postsynaptic Potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold

Inhibitory Postsynaptic Potentials (I P S Ps) are hyperpolarizations that move the membrane potential farther from threshold

(A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron)

Individual postsynaptic potentials can combine to produce a larger postsynaptic potential in a process called Summation

Vertebrates have three types of muscle, classified according to structure, function, and control mechanisms

• Cardiac muscle – found only in the heart

• Smooth muscle – surrounds and forms part of the lining of hollow organs and tubes

• Skeletal muscle – directly involved in locomotion.

Myofibrils are bundles of thick and thin filaments surrounding the nuclei

Each myofibril contains repeating units of filaments (sarcomeres)

ATP Synthesis

Oxidative fibers

• Contain numerous mitochondria and have a high capacity for oxidative phosphorylation

• Depends on blood flow to deliver oxygen and nutrients for ATP production

• Contain large amounts of myoglobin as an intracellular reservoir of oxygen

Glycolytic fibers

• Few mitochondria but a high concentration of glycolytic enzymes and large stores of glycogen

• Contain little myoglobin – makes them pale or white