MCAT - Biology

amino group, tetrahedral alpha carbon, alpha-carboxyl group, and variable R group

The 4 major structural components of each amino acid are:

peptide bonds and disulphide bridges

The two common types of covalent bonds between amino acids in proteins are…

carboxyl group, amino group, loss of water, repeat N-C-C pattern

A peptide bond is formed between the _______ of one amino acid and the ______ of another with the ______. The backbone of a polypeptide is thus a ________.

proteolysis or proteolytic cleavage, proteolytic enzyme or protease, peptide bonds

Hydrolysis of a protein by another protein is called _______ and the protein that does the cutting is called a ________. This is specific to the cutting of _______.

thiol (sulfhydryl, SH), disulphide, stabilising tertiary protein structure, cystine

The ____ of one cysteine can react with the same group on another cysteine to produce a ______ bond called a ______ bond. This plays an important role in _______. Once bonded, the cysteines are then referred to as ______.

disruption of protein structure without breaking peptide bonds

Denaturation refers to the…

urea (disrupts hydrogen bonds), extreme pH, extreme temperature, changes in tonicity (salt concentration)

Proteins can be denatured by _______, _______, _______, and _______.

sequence

A protein’s primary (1°) structure refers to…

hydrogen bonds between backbone groups, most commonly forming alpha helices or beta sheets

A protein’s secondary (2°) structure refers to…

parallel (strands run in the same direction) and anti-parallel (strands run in opposite directions)

Beta sheets come in two forms:

hydrophobic/hydrophilic interactions

A protein’s tertiary (3°) structure refers to…

interactions between polypeptide subunits to form multisubunit complexes

A protein’s quaternary (4°) structure refers to…

carbohydrates, carbon dioxide, oxidation

The principle energy source for cellular metabolism is ______, which can be broken down into ____ via ______.

Simple sugars, C_nH_2nO_n

“_____” refers to monosaccharides, which have the general chemical formula _______.

glycosidic linkage, covalent, dehydration, enzymatic catalysis

Monosaccharides can be bonded together to form complex sugars via ______, which is a _____ bond formed in a _______ reaction that requires _______.

sucrose, lactose, maltose, cellobiose

Common disaccharides include…

triglycerides store energy in adipose cells, phospholipids form the cell membrane, and cholesterol serves as a building block for the hydrophobic steroid hormones

Lipids play three physiological roles:

long unsubstituted alkanes that end in a carboxylic acid, 14-18 carbons long and synthesized 2 carbons at a time from acetate, carbon-carbon double bonds

Fatty acids are composed of _______, which is typically ________. A fatty acid without ______ is referred to as saturated, and a fatty acid with is referred to as unsaturated.

(Z) i.e. cis

The double bonds of unsaturated fatty acids are almost always in the _____ orientation.

micelle

Free fatty acids in an aqueous solution form a structure called a _______.

triacylglycerol or triglyceride, 3 fatty acids esterified into a glycerol

The storage form of fatty acids is fat, the technical name being _______, which is composed of _____.

hydrolyse fats

Lipases are enzymes that…

their hydrophobicity allows fat to pack more closely than carbohydrates which carry lots of water and fat molecules store more energy carbon-for-carbon

Fats are more efficient energy storage molecules compared to carbohydrates because…

phospholipids, diacylglycerol phosphate (DG-P)

Membrane lipids are ______ derived from _______.

Saturated fatty acids, because unsaturated fatty acids have kinked chains that have less contact with neighbouring groups

Would a saturated or unsaturated fatty acid residue have more van der Waals interactions with neighbouring alkyl chains in a bilayer membrane?

increase membrane fluidity, packing of hydrophobic lipid tails is disrupted thus the membrane is prevented from solidifying, Decreasing lipid tail length

Unsaturation in phospholipid fatty acids tends to ________ because _______. _______ also causes this effect.

membrane antifreeze, increases membrane fluidity, fluidity at an optimal level

Cholesterol is known as “_______” because at low temperatures it ________. Cholesterol keeps _______.

degree of saturation, tail length, amount of cholesterol

The structural determinants of membrane fluidity are:

isoprene (C₅H₈), (C₅H₈)_n

Terpenes are a class of compounds built from _______ with a general formula of ______.

limonene, 2, humulene, 3, taxadiene, 4

Monoterpenes (e.g. _____) consist of ___ isoprene units, sesquiterpenes (e.g. _____) consist of ___, and diterpenes (e.g. ______) consist of ___.

terpenoids, vitamin A (C₂₀H₃₀O)

Funtionalised terpenes are called ______, e.g. _____.

tetracyclic ring, cholesterol

All steroids have the basic ______ structure based on the structure of ______.

diet, synthesis in the liver, lipoproteins, atherosclerosis vascular disease

Cholesterol is obtained both by ______ and ______, where it is then carried in the blood packaged into ______ (one type of which has been implicated as the cause of _______).

pyrophosphate, anhydride linkage, P-O-P, high energy phosphate bond

Two phosphates bound together form _____, joined by a ______. The _____ in this is an example of a _______.

phosphate negative charges repel each other strongly, phosphate has more resonance forms and thus a lower free energy than linked phosphates, phosphate has a more favourable interaction with water than linked phosphates

Phosphate anhydride bonds hold so much energy because…

ribose or deoxyribose, purine or pyrimidine, carbon 1 of the ribose ring, 1-3 phosphates, carbon 5 of the ribose ring

Each nucleotide contains a _____ group, _______ joined to _______, and ______ joined to ______.

ATP

_____ is the universal short-term energy storage molecule

“transforming principle” exists when a harmless bacterium absorbed a mystery substance from a dead, deadly bacterium causing it to become deadly too

The Griffith experiment showed that a…

the mystery substance from the Griffith experiment was DNA by destroying proteins, RNA, and DNA one by one and transformation only stopped when DNA was destroyed

The Avery-MacLeod-McCarty experiment showed that…

DNA is the genetic mateiral by tracking bacteriophages, which showed that bacteriophages inject radioactively-labelled DNA (not protein) into bacteria to hijack them

The Hershey-Chase experiment showed that…

total amount of DNA in a given cell is constant, DNA replication is semi-conservative, in quiescent cells carbohydrates and proteins have a shorter half-life but DNA is not broken down, and DNA-altering chemicals or wavelengths induced phenotypic mutations

Additional evidence that initially supported that DNA was the genetic material, not proteins, was:

23

Each human has ____ pairs of chromosomes

homologous chromosomes

The two non-identical chromosomes in a pair are called…

Spermatogonia

Specialised cells in males that undergo meiotic division

Oogonia

Specialised cells in females that undergo meiotic division

prophase I → metaphase I → anaphase I → telophase I → prophase II → metaphase II → anaphase II → telophase II

The order of phases in meiosis is:

synapsis, bivalent or tetrad, recombination

Unlike mitosis, homologous chromosomes pair with each other during meiosis prophase I in ______, after which they are referred to as a _______. Then, ______ can occur.

synaptonemal complex (SC), early meiotic prophase I, SYCP2 and SYCP3 attach to each homologous chromatin structures that will be paired, lateral elements of the SC, align and attach with a central region

Synapsis is mediated by ________, which starts to form in _____. First, _______ which makes up the ______. These then ________.

alignment on the metaphase plate, tetrads are aligned rather than sister chromatids

In meiotic metaphase I, _______ occurs. Compared to mitosis, the difference is that…

separation of homologous chromosomes, haploid

During anaphase I, _________ occurs, after which the cell is then considered to be…

Nondisjunction

Failure of chromosomes to separate correctly during meiosis

trisomy 21

Down syndrome is caused by…

monosomy X

Turner syndrome is caused by…

two alleles of an individual are separated and passed on to the next generation singly

The law of segregation states that…

alleles of one gene will separate into gametes independently of alleles of another gene

The law of independent assortment states that…

one individual is crossed to another individual that is homozygous recessive, creating an F1 generation

A testcross is when…

probability of both of two independent events happening, i.e. P(A and B) = P(A) + P(B)

The rule of multiplication can be used to calculate…

probability of either of two events happening, i.e. P(A or B) = P(A) + P(B) - P(A and B)

The rule of addition can be used to calculate…

Incomplete Dominance

Phenotype of a heterozygote is a blend of both alleles, i.e. red parent + blue parent = purple daughter

Codominance

Phenotype of a heterozygote shows the traits of both alleles, but not blended, i.e. red parent + blue parent = red and blue daughter

Pleiotropism

Occurs when a single gene influences two or more distinct, and often seemingly unrelated, phenotypic traits

Polygenic

When a single trait is controlled by two or more independent genes working together

Penetrance

Likelihood that a person with a given genotype will express the expected phenotype

Epistasis

Expression of alleles for one gene is dependent on a different gene

Linkage

Failure of genes to display independent assortment

linkage

When genes are located on the same chromosome, they will display…

recombination frequency = number of recombinants / total number of offspring

The formula for the frequency of recombination for linked genes is:

hemizygosity, when an diploid organism only has one chromosome copy

An individual can not inherit mitochondrial traits from their father. Mitochondrial traits, like Y-linked or X-linked traits, are an example of _______, which is…

skipping generations and same number of affected males and affected females

An autosomal recessive trait can be identified using features like…

does not skip generations, number of affected males and affected females is the same, affected parent passes the trait to either all or half of offspring

An autosomal dominant trait can be identified using features like…

maternal inheritance, affected female effects all offspring, affected male effects no offspring, unaffected female can not have affected offspring

A mitochondrial trait can be identified using features like…

affects males only, affected male has all affected male offspring, unaffected male can not have affected male offspring

A Y-linked trait can be identified using features like…

skipping generations, affects more males than females, unaffected females can have affected male offspring, affected female has all affected male offspring but can have unaffected or affected female offspring

An X-linked recessive trait can be identified using features like…

does not skip generations, affects more males than females, affected males have all affected female offspring, affected females can have unaffected offspring and can pass the trait equally to female and male offspring

An X-linked dominant trait can be identified using features like…

inheritance of traits in population over time

Population genetics describes the…

members of a species that mate and reproduce with each other

In population genetics, a population is described as…

Gene Pool

Sum of all genetic information in a population

frequency of alleles in the gene pool of a population will not change over time

The Hardy-Weinberg law states that…

there is no mutation, no migration, no natural selection, is random mating, and population is sufficiently large to prevent random drift

The Hardy-Weinberg law assumes that…

p² + 2pq + q² =1 where p is dominant and q is recessive

The Hardy-Weinberg equation is:

allele frequencies no longer change

At Hardy-Weinberg equilibrium…

Directional Selection

Natural selection favours individuals with one extreme version of a trait (either end of a bell curve distribution), causing the overall population to shift in that direction over time

Divergent Selection

Natural selection wherein one single species splits into two or more different groups, and each group evolves unique traits because they live in different environments

Stabilizing Selection

Natural selection where the environment favours individuals with average traits instead of extreme ones, helping a population stay the same over time

Artificial Selection

Humans intervene in the mating of the species to achieve desired traits rather than letting the environment decide

Sexual Selection

Natural selection wherein a species evolves special traits to attract mates and reproduce, even if those traits do not help them survive

Kin Selection

Natural selection wherein a species helps its family members survive and reproduce, even if it hurts the helper’s own survival

group of organisms that are capable of reproducing with each other

A species is defined as a…

Prezygotic Reproductive Isolation

Barriers that prevent the formation of a hybrid zygote, e.g. individuals who could mate live in different habitats and thus cannot access each other

Postzygotic Reproductive Isolation

Barriers that prevent the development, survival, or reproduction of hybrid individuals, e.g. hybrid offspring is born but can not reproduce in adulthood (e.g. mule) or hybrid offspring do not develop normally and die as embryos

speciation

The creation of a new species is called…

Cladogenesis

Branching speciation where one species diversifies and becomes 2 or more species

Anagenesis

Speciation where 1 species becomes another by changing so much that if an individual were to go back it would be unable to reproduce with its ancestors

Allopatric Speciation

Cladogenesis initiated by geographical isolation

Sympatric Speciation

A species gives rise to a new species in the same geographical area, such as through divergent selection

Homologous Structures

Physical features that have been retained by different species as a result of a common ancestor

Analogous Structures

Physical features that share the same function between species but are not due to common ancestry

Convergent Evolution

Different species come to possess many analogous structures due to similar selective pressures, e.g. bats and birds

Divergent Evolution

Divergent selection causes cladogenesis

Parallel Evolution

Different species go through similar evolutionary change due to similar selective pressures, e.g. all organisms in an ice age are selected for ability to tolerate the cold