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MCAT > Biology > Flashcards

Biology Flashcards

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MCAT flashcards
1
Q

Wobble Pairing

A

A pairing between two nucleotides that is not a Watson-Crick base pair (G-C and A-U).

Wobble pairing in the third base of the codon is the reason for the redundancy in the genetic code. For example, the codons GCU, GCC, GCA, and GCG all code for the amino acid alanine.

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2
Q

Euchromatin

A

Less condensed regions of chromosomes containing genes that are under active transcription.

Histone acetylation can convert heterochromatin into euchromatin by removing the positive charge from lysine residues on histone proteins, which reduces the attraction between the negative-charged DNA and positively-charged histone proteins.

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3
Q

Law of Segregation

A

The pair of alleles for a given trait separate during meiosis so that each gamete receives only one allele. During fertilization, the new offspring receives one allele from each parent when the two gametes fuse.

Gregor Mendel discovered the law of segregation when he performed monohybrid crosses with pea plants. He observed that the traits of the offspring did not always match those of the parents.

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4
Q

Desmosome

A

A cell-cell junction that holds the two cells together.

Adjacent epithelial cells of the skin are held together by desmosomes to prevent the skin from pulling apart easily.

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5
Q

Multipotent Stem Cells

A

Stem cells capable of forming several cell types in the body but are more limited than pluripotent stem cells.

Hematopoietic stem cells are multipotent and capable of forming lyphocytes, erythrocytes, platelets, and several other cells types.

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6
Q

Proto-Oncogene

A

Proto-oncogenes are a group of genes in the cell that can be mutated into an oncogene.

Proto-oncogenes normally function in the cell to stimulate cell division, inhibit cell differentiation, and inhibit apoptosis.

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7
Q

Apoptosis

A

Programmed cell death

Apoptosis is a highly regulated process that can be triggered by both internal and external stimuli. The process begins by the release of cytochrome C from mitochondria that then activates caspase enzymes that carry out the destruction of the cell from the inside.

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8
Q

Nonsense Mutation

A

A point mutation where the substituted nucleotide results in a premature stop codon.

The point mutation UAC to UAG is nonsense mutation.

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9
Q

Passive Transport

A

The transportation of molecules across the cell membrane without using energy.

In passive transport, molecules move from a region of higher concentration to a region of lower concentration.

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10
Q

Totipotent Stem Cells

A

Stem cells capable of forming every cell type in the body and the placenta.

A single totipotent cell is capable of forming an entire fertile adult individual.

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11
Q

Nucleoside

A

A nitrogenous bases bonded to a ribose or deoxyribose sugar.

Adenosine is a nucleoside consisting of an adenine nitrogenous base and a ribose sugar. Adenosine triphosphate (ATP) is a nucleoside triphosphate.

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12
Q

Point Mutation

A

A mutation in DNA where one nucleotide is substituted for another.

Point mutations can result in a silent mutation, a missense mutation, or a nonsense mutation.

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13
Q

Determination

A

The process of a cell taking on an irreversibly acquired fate.

Once a cell is determined, it is committed to forming a specific type of cell.

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14
Q

Gap Junction

A

A cell-cell junction that allow the free passage of ions and small molecules between the two cells.

Cardiac muscle cells in the heart contain gap junctions to allow the contraction signal to pass efficiently from cell to cell.

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15
Q

Alternative Splicing

A

The process of excising different combinations of introns and exons from the pre-mRNA to form mRNA.

Alternative splicing allows for different protein products to be produced from the same gene. For example, an exon that is translated in the protein in one cell may be spliced out in another cell, yielding a shorter protein product.

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16
Q

Phenotype

A

The physical manisfestation of an organism, including physical traits and behavior.

The phenotype is determined by the genotype and the organism’s interactions with the environment.

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17
Q

Spliceosome

A

A large ribonucleoprotein complex that removes introns from a pre-mRNA molecule and ligates the remaining exon fragments together to produce mRNA.

The spliceosome is the RNA and protein complex that performs alternative splicing.

18
Q

Stop Codons

A

UAA, UGA, UAG

Mnemonic: You(U) Are Annoying (UAA), You(U) Go Away (UGA), You(U) Are Gone (UAG)

19
Q

Pluripotent Stem Cells

A

Stem cells capable of forming every cell type in the body but cannot form the placenta.

Induced pluripotent stem cells can be produced by forcing adult somatic cells to express certain genes and transcription factors.

20
Q

Senescence

A

A state of growth arrest in which a diploid cell ceases to divide.

Senescence can be triggered by telomere erosion or cell damage and is considered an alternative to apoptosis.

21
Q

A cell-cell junction that forms a seal preventing the flow of water and solutes in the space between the cells.

The epithelium of the small intestine contains tight junctions that prevent unwanted substances from entering the circulatory system.

A

Tight Junction

22
Q

Differentiation

A

The process of a cell changing from one cell type to another, usually to a more specific cell type.

Differentiation occurs after a cell undergoes determination.

23
Q

Active Transport

A

The transportation of molecules across the cell membrane using energy.

In active transport, molecules move from a region of lower concentration to a region of higher concentration.

24
Q

Microtubules

A

The thickest of the three cytoskeletal fibers and composed of tubulin polymers.

Cilia, flagella, and the mototic spindle are all composed of microtubules. Microtubules also play an important role in the transport of vesicles, proteins, and organelles in the cell.

25
Q

Central Dogma

A

The genetic information stored in DNA is transcribed into messenger RNA that is then translated into a particular protein.

Retroviruses are an exception to the central dogma because they contain the enzyme reverse transcriptase that can convert RNA into DNA.

26
Q

Chemotaxis

A

The movement of an organism or cell in response to chemical stimuli.

The movement of sperm toward the egg is an example of chemotaxis.

27
Q

Start Codon

A

AUG

While the AUG start codon codes for the amino acid methionine, the three stop codons do not code any amino acid.

28
Q

Missense Mutation

A

A point mutation where the substituted nucleotide results in a codon that codes for a different amino acid.

The point mutation GGU to GAU is a missense mutation that changes the amino acid in the peptide from glycine to aspartic acid.

29
Q

Genotype

A

The complete set of genes in an organism or the pair of alleles for a gene carried by an organism.

A genotype is homozygous if both alleles are identical and heterozygous if the two alleles are different.

30
Q

Cancer

A

A collection of diseases where the body’s cells grow uncontrollably and spread to other parts of the body.

Cancer can be inherited (genetic transmission) or induced by environmental factors.

31
Q

Mutagen

A

A physical or chemical agent capable of mutating the DNA in an organism.

UV rays, X-rays, gamma rays, reactive oxygen species, and viruses are all examples of mutagens.

32
Q

Reverse Transcriptase

A

An enzymes that produces complementary DNA from an RNA template.

Retroviruses such as HIV contain the reverse transcriptase enzyme.

33
Q

Tumor Suppressor Gene

A

Tumor suppressor genes are a group of genes in the cell that may lead to tumor development when inactivated.

Tumor suppressor genes normally function in the cell to repress cell division, repair damaged DNA, and promote apoptosis.

34
Q

Nucleotide

A

A nitrogenous base bonded to a ribose or deoxyribose sugar and at least one phosphate group.

Adenosine triphosphate (ATP) is a nucleotide consisting of an adenine nitrogenous base, a ribose sugar, and three phosphate groups.

35
Q

Intermediate Filaments

A

The intermediate in diameter of the three cytoskeletal fibers and is composed of various protein molecules.

Intermediate filaments are an important structural component of many cells and tissue types.

36
Q

Oncogene

A

A mutated version of a proto-oncogene that typically has increased activity.

Oncogenes cause increased cell division, decreased cell differentiation, and inhibition of apoptosis that may contribute to the formation of cancer.

37
Q

Microfilaments

A

The thinnest of the three cytoskeletal fibers and composed of actin filaments.

Microfilaments are involved with muscle contraction, cellular movement, and cytokinesis

38
Q

Viroids

A

An infectious subviral particle consisting entirely of a circular, single-stranded RNA molecule.

Viroids do not code for any protein products but are capable of self-replication and causing diseases.

39
Q

Prions

A

An infectious subviral particle consisting entirely of a misfolded protein.

Prion proteins are typically expressed in the body in a normal form. They may take on a misfolded form and become infectious agents that can convert other normal prion proteins into the misfolded form, leading to neurodegenerative diseases.

40
Q

Law of Independent Assortment

A

Alleles for different genes separate independently from each other during meiosis.

Gregor Mendel discovered the law of independent assortment when he performed dihybrid crosses with pea plants. He observed that the combination of traits in the offspring did not always match those of the parents.

41
Q

Gene Pool

A

The set of all genes in a population.

A large gene pool is indicative of high genetic diversity.

42
Q

Heterochromatin

A

Highly condensed regions of chromosomes that are transcriptionally inactive.

In females, one X chromosome forms the transcriptionally inactive heterochromatin structure called the barr body.

MCAT (6 decks)

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