MCAT Biology

Microtubules are used

-in the transport of vesicles and the positioning of organelles within the cell.

-microtubules form the spindle apparatus that is an essential part of both mitosis and meiosis.

-they are composed of dimers of the protein tubulin

Endoplasmic Reticulum

A system of membranes that is found in a cell's cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids (lipids made in smooth ER).

Golgi apparatus

A system of membranes that modifies and packages proteins for export by the cell

Peroxisomes

Produce hydrogen peroxide; detoxify harmful substances such as ethanol and break down long fatty acids to medium length fatty acids

microfilaments

-composed of two strands of actin polymers

-play a role in cell motility

-play a role in endocytosis and exocytosis

-help with cell cleavage

Microtubules

-slightly wider than microfilaments

-composed of polymeric dimers of polymers known as alpha-tubulin and beta-tubulin

-maintain cell strucutre and make up cilia and flagella

-facilitate intracellular transport and make up mitotic spindles

intermediate filaments

-structural support and cellular adhesion

(ex. keratin)

centrioles

-cylindrical structures made up of tubulin and help organize the mitotic spindle

-important constituent of the centrosome (microtubule organizing center)

prokaryotic flagella vs eukaryotic flagella

powered by ATP in eukaryotes and bacteria powered by a rotary motion powered by a proton gradient

cell cycle

cell cycle (look up video)

G0 phase

resting phase of cell cycle

interphase

broken up into G1, S, and G2

cell grows during G1 and G2 and replicates during S

G1 checkpoint

restriction point, when a cell commits to division

G2 checkpoint checks for DNA damage

Prophase

Chromosomes become visable, nuclear envelop dissolves, spindle forms

kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

telophase

opposite of prophase

-new nuclear envelope, nucleolus reappears with nucleus

look up meiosis video

Prokaryotic translation relies on the presence of several release factors.

In contrast, eukaryotes need only one such factor: eukaryotic translation termination factor 1 (eRF1).

histones in human nucleosomes:

H1, H2A, H2B, H3, H4,

In a negative inducible operon, transcription is inhibited by a

repressor; this results in a basal transcription rate near zero. However, transcription can be "switched on" by the addition of an inducer protein, which blocks the repressor from binding to the operon.

Activators bind to DNA sequences and help "recruit" promoters to start transcription.

They are known to upregulate transcription in positive operons, and in the negative lac operon, the cAMP activator protein (CAP) helps promote the transcription of the genes needed for lactose metabolism. However, for CAP to work, the repressor must have also been removed by an inducer (allolactose in the case of the lac operon).

Enhancers are

regulatory DNA sequences found only in eukaryotes. In prokaryotes, the operator serves as the regulatory DNA region instead.

Oncogenes

are genes that are involved in cell growth and have the potential to cause cancer. Duplication of oncogenes would result in the upregulation of cell growth cell division, potentially leading to uncontrollable mitosis.

Cell cycle checkpoint genes are a type of

tumor suppressor gene. They prevent premature cells from undergoing mitosis. For this reason, their amplification would make the cell more resistant to uncontrollable division.

Tumor suppressor genes

also known as antioncogenes, regulate cell division. Increased transcription of these genes would reduce the risk of cancer.

Inhibitors disable

activators

Repressors bind to

operators to reduce transcription

Nucleases are enzymes that

cleave nucleic acids. The addition of such enzymes would break down the DNA

Proto-oncogene

a gene that regulates normal cell division but that can become a cancer-causing oncogene as a result of mutation or recombination

Proto-oncogenes do not necessarily exhibit either a greater or lesser rate of transcription in cancer patients.

Acetylation __________ gene expression, while methylation __________ it.

promotes, discourages

Methylation of a gene _______ its proclivity to undergo transcription.

lowers

Small nucleolar RNAs (or snoRNAs)

are involved in the modification of rRNA. As such, they would be located in the nucleolus, where ribosomes are assembled.

snRNA, or small nuclear RNA

is found in the nucleus. These molecules aid in the splicing of pre-mRNA.

hnRNA is simply an alternative name for

pre-mRNA. As such, not only is this type of nucleic acid found in the nucleus, it also (at least partially, in its exons) codes for peptide products.

tRNA molecules are most likely to be found in the

cytoplasm

a test cross

a mating between the unknown individual and an individual known to be homozygous recessive (rrll) for the traits in question

Southern Blot

What blotting technique uses the following for analysis? • DNA

Northern Blot

Similar technique [to Southern], except that Northern blotting involves radioactive DNA probe binding to sample RNA .

Western blot

protein

eastern blotting

analyze post-translational modification of peptides

wild type

the traits an animal typically possesses when found in nature. This usually refers to a dominant trait, but not always. If nearly all of the coyotes now have spotted fur, then spotted fur is the wild type.

In humans, females have two of the same sex chromosome (XX), while males have only one X and one Y. However, the X chromosome is much larger and carries significantly more genes than the Y version. To balance their genetic load with that of males...

one of each female's X chromosomes is inactivated.

Virtually all of the cellular machinery and organelles are maternally inherited. Paternal organelles are destroyed during fertilization.

including the mitochondria, golgi apparatus, and lysosomes

Mitochondria divide and segregate to daughter cells...

randomly, so it is possible for some gametes to have more mutated mitochondria than others.

At the end of meiosis I, cells are already haploid, though they are still paired with their identical sister chromatids.

For this reason, the 46 chromosomes present in a typical somatic cell have already been reduced to 23 by the time that prophase II is reached.

The nuclear membrane temporarily disintegrates in both

prophase II and mitotic prophase.

Sister chromatids are pulled apart in

anaphase

look up mitosis and meiosis vids

khan academy

Genes that are sufficiently close together on a chromosome will tend to

"stick together," and the versions (alleles) of those genes that are together on a chromosome will tend to be inherited as a pair more often than not.

This phenomenon is called genetic linkage. When genes are linked, genetic crosses involving those genes will lead to ratios of gametes (egg and sperm) and offspring types that are not what we'd predict from Mendel's law of independent assortment.

recombination frequency

So, we can say that a pair of genes with a larger recombination frequency are likely farther apart, while a pair with a smaller recombination frequency are likely closer together.

Importantly, recombination frequency "maxes out" at 50\%50%50, percent (which corresponds to genes being unlinked, or assorting independently). That is, 50\%50%50, percent is the largest recombination frequency we'll ever directly measure between genes.

Remember the difference between homologous chromosomes and sister chromatids!

Homologous chromosomes are the pairs of non-identical chromosomes that are present in every somatic cell. (For example, you inherit one version of chromosome 2 from your father and one from your mother; these structures are homologous.) These pairings separate during meiosis I, causing the daughter cells generated by this process to be haploid before the start of meiosis II.

In which of these stages do homologous chromosomes separate into distinct cells?

Anaphase of meiosis I

synaptonemal complex is a

protein-based linkage that appears during meiosis and connects homologous chromosomes. As these chromosomes must be closely situated to facilitate crossing over, issues could arise involving genetic recombination or synapsis.

The synaptonemal complex does not function during mitosis.

hardy-weinberg equil

Genetic drift

is simply the change in allele frequencies due to random processes. Specifically, random chance plays a role in determining which alleles are inherited by offspring from their parents. This can cause some alleles not to be passed down at all, leaving others "fixed" as the only alleles present for that locus. However, genetic drift does not relate to the introduction of new alleles (as mutation does), and cannot increase a population's genetic diversity.

Sympatric speciation

is that which occurs without a physical barrier. A population that diverges into two separate species in a single cave falls under this form of speciation.

Parapatric speciation

speciation pattern in which populations speciate while in contact along a common border

occurs when segments of two distinct populations overlap. Due to environmental differences, these segments may develop into two species, but individuals in the overlapping areas can typically still interbreed.

Allopatric speciation

occurs when populations, or parts of the same population, are separated by a physical barrier. Peripatric speciation is a subtype of this concept that occurs specifically when one of the two populations is much smaller than the other.

Convergent evolution

occurs when entirely separate lineages gradually appear more similar over time. Here, bats, birds, and butterflies are very distantly related, but all evolve to possess wings through different mechanisms. In the end, these species resemble each other despite their genetic differences.

Parallel evolution

happens when closely related species evolve in a similar way over time. This differs from the question stem, where the three types of organism did not previously resemble each other as strongly.

Coevolution

requires that two species evolve in response to each other. The question gives no indication that bats evolved in part "because" birds did so, for example.

Divergent evolution

In this phenomenon, two closely related lineages gradually become more dissimilar.

Mutualism

is a symbiotic relationship in which both parties benefit. Ex. the ants feed the fungus and the fungus feeds the ants.

Commensalism

involves a benefit to only one participating species; the other species is unaffected.

Parasitism

occurs when one organism benefits from the relationship at the expense of the other

Ectosymbiosis

is a specific phenomenon in which one species lives on the surface of another.

cells walls contain

peptidoglycan

Gram-negative bacteria

Bacteria that have a thin peptidoglycan cell wall covered by an outer plasma membrane. They stain very lightly (pink) in Gram stain. Gram-negative bacteria are typically more resistant to antibiotics than Gram-positive bacteria.

Gram-positive bacteria

Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.

Bacteria replicate by

binary fission

transformation

process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria

viruses with envelopes are ____ sensitive to outside factors

more

Virion

a fully formed virus that is able to establish an infection in a host cell

Prion

misfolded proteins that causes other proteins to become misfolded

Viriods

infectious particles found in plants that can silence gene expression by binding to specific RNA sequences

lytic pathway

Bacteriophage replication pathway in which a virus immediately replicates in its host and then causes it to lyse, releasing progeny phages (so no integration into host genome)

lysogenic pathway

Bacteriophage replication path in which viral DNA becomes integrated into the host's chromosome and then it replicates and lyses releasing progeny phages

double membrane bound organelles in eukaryotic cells

mitochondria, ER, Golgi body, and nucleus

anterograde vesicles

vessicles leaving ER with newly formed protein cargo, go to golgi after

cholesterol in plasma membrane

stabilizes the structure of the plasma membrane when the temperature changes, this reduces fluidity

lysosomes

digest proteins

(while proteosomes perform functions related to the pentose phosphate pathway and the neutralization of active oxygen species)

the inside of the rough ER lumen is similar to...

the extracellular space

because proteins are synthesized in the rough ER lumen , and for these proteins to function they must be folded under conditions similar to those in the extracellular environment

gap junctions

only allow small molecules through

Topoisomerase

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

fluid mosaic model

The mentioned model involves two main aspects: "fluid" and "mosaic." The "fluid" aspect refers to the ability of component molecules to travel laterally within their leaflet of the bilayer, while the word "mosaic" denotes the presence of proteins and other molecules that are scattered in a mosaic within its structure.

fluidity of a membrane

We are looking for characteristics of a membrane that increase fluidity, especially in cold environments. Unsaturated fatty acids increase fluidity in general, due to the presence of "kinks" in their structure. Cholesterol and similar molecules, which act as a type of buffer system for membrane fluidity, are slightly more complex. Large amounts of cholesterol decrease fluidity at high temperatures but increase it at low temperatures.

sodium potassium pump, how many in/out

The Na+/K+ pump helps the cell maintain its membrane potential and creates a concentration gradient. It does this by moving sodium out of the cell and transporting potassium inward.

It pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell.

the Na+/Ca2+ exchanger must

move calcium ions out of the cell.

After a molecule has been engulfed via endocytosis, in what order does it progress through membrane-bound compartments before it is degraded?

Early endosome, late endosome, lysosome

Goldi apparatus

The Golgi apparatus functions like a cellular "post office." It receives proteins from the endoplasmic reticulum and packages them into vesicles; these membrane-bound sacs can then travel to specific locations within the cell or to the plasma membrane for excretion. Additionally, lysosomes are formed from vesicles that bud off the Golgi's larger structure. However, note that choice D references enzyme production. Since nearly all enzymes are protein-based, it is the ribosomes - whether free-floating or attached to the rough ER - that synthesize them.

Rough ER

synthesis of transmembrane proteins

Nucleolus

rRNA production and ribosome assembly

lysosomes

facilitate the enzymatic catabolism of protein

Peroxisomes

are small membrane-bound organelles that function mainly to break down lipids

removal of the ER

Removal of the ER might disrupt the outer leaflet of the nuclear envelope, potentially releasing the contents of the nucleus into the cell and triggering apoptosis.

Macrophages must undergo ____ during phagocytosis. If a macrophage cannot engulf bacteria in this

rapid actin reorganization

If a macrophage cannot engulf bacteria in this manner, its overall function would be considered very impaired.

collagen

is not a cytoskeletal polymer; it is an extracellular fiber that is secreted by certain cell types.

Microtubule linking proteins

as their name implies, are used to bind bundles of microtubules together. This is most notably observed in eukaryotic flagella. If these proteins cannot be synthesized, flagella will not work properly, and the function of cells that rely on these structures will be diminished. Of the listed cells, only spermatozoa (sperm cells) possess flagella.

Keratin fibers extend across epithelial cells (in the skin, for example) to link adjacent cells via structures called desmosomes.

As a type of intermediate filament, keratin possesses high tensile strength; as such, it can form a network of fibers that distribute mechanical stress among the cells of an epithelial layer. Keratin is therefore the cytoskeletal protein that contributes most to the skin's stretching ability.