Polypeptide synthesis occurs through transcription and translation. In transcription, DNA in the nucleus is transcribed into messenger RNA (mRNA) by RNA polymerase, which binds to the promoter region, unzips the DNA, and synthesizes an mRNA strand complementary to the DNA template. In translation, the mRNA leaves the nucleus and binds to a ribosome in the cytoplasm, where transfer RNA (tRNA) brings amino acids to the ribosome. The anticodon on the tRNA pairs with the corresponding codon on the mRNA, and the ribosome adds amino acids to the growing polypeptide chain until a stop codon is reached.
Eukaryotic chromosomes are linear DNA molecules tightly packed with proteins called histones. The DNA wraps around histones to form nucleosomes, and further coiling creates the compact structure of a chromosome. Genetically, they consist of multiple genes, regulatory sequences, and non-coding regions like introns. Chromosomes are diploid in somatic cells and carry genetic information in a sequence of nucleotide bases.
Air has a low specific heat capacity, heating and cooling quickly, while water has a high specific heat capacity, absorbing and retaining heat, providing a more stable environment.
The Y chromosome carries the SRY gene, which triggers the development of testes in the embryo. The testes then produce testosterone, leading to the development of male secondary sexual characteristics.
DDT is a persistent organic pollutant that accumulates through bioaccumulation and biomagnification. Birds consume contaminated prey, and the concentration of DDT increases at each trophic level, leading to high levels in top predators like birds of prey, which can cause reproductive issues such as eggshell thinning.
Humans regulate body temperature through thermoregulation mechanisms like sweating, primarily controlled by the hypothalamus. When body temperature rises, thermoreceptors in the skin send signals to the hypothalamus, which triggers sweat glands to release sweat onto the skin surface. As sweat evaporates, it absorbs heat from the body, cooling the skin and lowering internal body temperature. Blood vessels near the skin surface dilate, increasing blood flow and heat dissipation, helping maintain homeostasis.
Simple diffusion is the movement of small, non-polar molecules (e.g., oxygen) across the membrane from high to low concentration without energy use.
When the temperature exceeds the optimal level, enzymes begin to denature, losing their structure and function due to the breaking of hydrogen bonds.
The sequence of events during mitosis includes: Prophase (chromosomes condense, nuclear envelope dissolves, spindle fibers form), Metaphase (chromosomes align at the cell's equator), Anaphase (sister chromatids are pulled apart), Telophase (chromatids de-condense, nuclear envelope re-forms), and Cytokinesis (cytoplasm divides, resulting in two identical daughter cells).
The optimal temperature for human enzymes is usually around 37°C.
Proteins have various functions in cells, including providing structural support (e.g., collagen), catalyzing biochemical reactions (e.g., DNA polymerase), transporting molecules across membranes (e.g., hemoglobin), signaling (e.g., insulin), and defending against pathogens (e.g., antibodies).
Animals in air habitats may rely on insulation, such as fur or feathers, to maintain body temperature due to greater temperature fluctuations.
Lower temperatures reduce the kinetic energy of molecules, decreasing enzyme-substrate collisions and slowing reaction rates.
Types of mutations include point mutations (single nucleotide changes), frame-shift mutations (insertions or deletions that shift the reading frame), nonsense mutations (premature stop codons), and missense mutations (substituting one amino acid for another). An example is sickle cell anemia, caused by a point mutation in the hemoglobin gene.
Facilitated diffusion is the transport of larger or polar molecules (e.g., glucose) through protein channels from high to low concentration, without energy.
Active transport is the movement of molecules against their concentration gradient using energy (ATP). An example is the sodium-potassium pump.
Rotenone inhibits the electron transport chain in the mitochondria, blocking the transfer of electrons to oxygen. This halts ATP production during oxidative phosphorylation, leading to energy deficiency and ultimately cell death. Without ATP, critical cellular processes cannot occur.
Factors that impact ecosystem stability include biodiversity (greater diversity increases resilience), keystone species (like wolves in Yellowstone that maintain balance), resource availability (consistent access to water, food, and nutrients), climate (stable climates support consistent ecosystems), and human activity (deforestation, pollution, and climate change can destabilize ecosystems).
