Biology Flashcards
Wobble Pairing
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.
Euchromatin
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.
Law of Segregation
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.
Desmosome
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.
Multipotent Stem Cells
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.
Proto-Oncogene
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.
Apoptosis
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.
Nonsense Mutation
A point mutation where the substituted nucleotide results in a premature stop codon.
The point mutation UAC to UAG is nonsense mutation.
Passive Transport
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.
Totipotent Stem Cells
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.
Nucleoside
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.
Point Mutation
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.
Determination
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.
Gap Junction
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.
Alternative Splicing
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.
Phenotype
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.
Spliceosome
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.
Stop Codons
UAA, UGA, UAG
Mnemonic: You(U) Are Annoying (UAA), You(U) Go Away (UGA), You(U) Are Gone (UAG)
Pluripotent Stem Cells
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.
Senescence
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.
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.
Tight Junction
Differentiation
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.
Active Transport
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.
Microtubules
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.
