SAT Biology EM Review

SAT Biology E/M Review Molecules of Biology Molecules that contain carbon are organic, whereas molecules that do not are inorganic. Except for carbon dioxide (CO2) Proteins: Proteins are a chain of amino acids. They share a 'backbone' (R is where they differ) When they bond they form peptide bonds, which are formed by dehydration synthesis. The reverse process is called hydrolysis. Carbohydrates: Carbs are made of saccharides, and are essentially sugar. The generic chemical formula for a monosaccharide (one saccharide) is CnH2nOn (eg. C6H12O6, glucose and fructose) Glucose and fructose differ in arrangement of atoms. Glucose can also form a ring structure. Disaccharides: Maltose and sucrose Maltose= 2 glucose (C12H22O11) Sucrose = glucose + fructose (C12H22O11) Polysaccharides: Glycogen, starch, and cellulose (all polymers of glucose, but linking differs) Glycogen: the form animals store glucose Starch: the form plants store glucose Cellulose: a structural polysaccharide that forms plant walls. Lipids: Lipids are fats, and are hydrophobic. (Another term for hydrophobic is nonpolar) 3 common forms: triglycerides, phospholipids, and cholesterol Triglycerides = 3 fatty acids bonded to a glycerol molecule. Animals store fat this way and this is the fat you eat Phospholipids = 2 fatty acids and a phosphate bonded to a glycerol molecule. The phosphate is hydrophilic, ie polar. They can form a double layer (lipid bilayer) to create a cell membrane. Cholesterol = fatty acids form rings. Only in animal cells. Hormones derived from Cholesterol. Nucleic Acid: Nucleic Acid is DNA and RNA. The monomer is a nucleotide. Nucleotides are Adenine, Guanine, Cytosine, and Thymine. When they form a chain, it is a string of DNA. DNA is double stranded, and only specific nucleotides bond to each other. Adenine and Thymine are a pair, and Guanine and Cytosine are a pair. RNA is similar, but only one stranded and thymine is replaced by uracil. Cell Structure Eukaryotic Cell Structure: Cell Wall and/or membrane, Cytoplasm and Nucleus • • • Cell wall and membrane is outer layer (animals have only membrane) Cytoplasm contains the organelles Nucleus contains chromosomes Cell Walls (Plants = cellulose, Bacteria = peptidoglycan, Fungi = chitin) are lipid bilayers Fatty acids are hydrophobic, hydrophilic substances do not like to cross the oily barrier. The barrier is selectively permeable. Simple Diffusion: Substance moving from high concentration to low concentration Only hydrophobic substances can move (oxygen, carbon dioxide, and cholesterol) Facilitated Diffusion: Crossing molecules are hydrophilic (sodium, potassium, calcium, and glucose) Proteins form specialized channels like pores across the membrane. Channel only works for particular substances. Some proteins act as a carrier molecule, pull a substance through the membrane. Active Transport: Can move substance across the cell membrane from area of low concentration to an area of higher concentration. Requires energy (as opposed to passive) Bulk Transport: Moving large bulky item across membrane. Takes in a particle by engulfing it in pocket called vesicle. Called endocytosis going in to cell, exocytosis when leaving cell. Osmosis: Movement of water from high concentration to low concentration. Note that water concentration gradient is opposite to the solute gradient. The more particles, the less water, the more water, the less particles. Cells have to be put into exactly the same concentration of water (isotonic), or the cell will shrivel or swell. When put into concentrated (hypertonic) solution, there is more concentration of cells outside so water gets sucked out, the cell shrivels. In watery (hypotonic) solution there are more particles in the cell, so water will get sucked in and the cell will explode. Cytoplasm: Vacuole: Storage of waste Ribosomes: Protein synthesis Smooth endoplasmic reticulum: membranes and tubes to transport stuff around cell Rough endoplasmic reticulum: Endoplasmic reticulum with ribosomes bound to it. They specifically synthesize membrane proteins (like channels) or secreted proteins. Golgi apparatus: sorts and packages proteins made by ribosomes Mitochondria: Function in cellular respiration; produce ATP; bound by double membrane Lysosomes: Digest foreign substances and worn out organelles Centrioles: Help form the spindle during mitosis Nucleus: Control center, contains DNA Nucleolus: Site of ribosome synthesis Cell membrane: Outer membrane that regulates what comes in and goes out of cell Enzymes: Enzymes are catalysts. It has spaces on it that fit specific molecules. By bringing together specific molecules it starts reactions. Those places are called active sites. When an enzyme catalyzes a reaction, it is not ‘used up’. Enzymes are specific for particular reactions. Reactants are called substrates Enzymes are nothing more than proteins. If they lose their shapes (become denatures) they can no longer run reactions. Some need coenzymes. Vitamins are coenzymes. Transcription and Translation The nucleus contains the cell’s genetic information. DNA in eukaryotes is found in several pieces. Each piece is called a chromosome Chromosomes are different from pair to pair and person to person. Replication: 1) Double helix unwinds, strands separate 2) DNA polymerase lines up nucleotides to form second strand 3) Hydrogen bonds form between base pairs. Bonds form between the sugar-phosphate. 4) Twist up into double helixes DNA acts as a template for new complementary strands. Chromosomes: Every somatic (non-sex) cell has 46 chromosomes, identical to 46 in every other cell 23 pairs of chromosomes, each pair is called a homologous pair. Cells with two sets of chromosomes are called diploid. Their job is to carry instructions for making proteins, ie enzymes. Enzymes can make everything else needed. Transcription and Translation: RNA is single stranded Process goes from language of nucleotides to language of nucleotides to language of amino acids. Copy from one language to same language = transcription (DNA-RNA) Copy from one language to diff language = translation (RNA - proteins) Enzyme RNA polymerase creates complementary strand RNA Only part of DNA is transcribed to make RNA, because not all of DNA has instructions for protein synthesis. The parts that do are called genes. mRNA = messengerRNA, carries the info for protein synthesis rRNA = ribosomalRNA, catalyst for protein synthesis, makes ribosomes functional tRNA - transferRNA, carries amino acids from the cytoplasm to the ribosomes (Replication and transcription are in nucleus, translation happens in cytoplasm) 3 nucleotides = codon = code for specific amino acid Codons are read in non-overlapping sequence AUG codon = start codon UAA, UAG, UGA codons = stop codons How translation works: tRNA has amino acid attachment site on one side, anticodon loop on the other. Anticodon loop = region where tRNA can base pair with codons on mRNA (must have the correct complementary codon. The amino acid that connects is the one that corresponds to the mRNA codon) 1) mRNA binds to ribosome in two places (A and P sites, p for peptide) 2) two tRNAs comes with amino acids, base pairs with mRNA, ribosome forms peptide bond between two amino acids, first tRNA leaves, ribosome slides down one codon. second tRNA now occupies first position 3) second position now occupied with 3rd mRNA codon. New tRNA comes. Old tRNA leaves, ribosome moves over. 4) Process continues, moving down the mRNA strand until stop codon is reached. Cracking Evolution and Diversity Evolution: Life appeared about one billion years ago. The Earth mostly hydrogen, ammonia, methane, and water. The first cells were heterotrophs (ie could not synthesize their own food) Food was scarce, so organisms evolved to make their own food using solar energy. DNA mutation: error made during DNA replication, leads to a change in gene pool, creating genetic variability. Genetic variability is caused by random mutation. Mutations only get passed on from sperm or ovum. Evolution occurs because better competitors are better at staying alive, therefore have a better chance of reproducing. This is natural selection. Environment changes can cause evolution. (a different set of challenges puts different competitors in the lead, leading to more of their offspring) Different species = can’t mate. Divergent evolution causes speciation, so much change in populations they can’t have offspring anymore. Convergent evolution causes similar traits and behavior. Cannot merge species, or create a new species. Convergent evolution = Analogous structures. Similar but not from common ancestor. Homologous structures = common in species that share ancestors. Vestigial structures = useless structures (that used to have purpose in former selves), appendix in humans, leg bones in snakes Phylogeny: Phylogeny = evolutionary relationships Domain - Kingdom - Phylum - Class - Order - Family - Genus – Species Carolus Linnaeus: came up with modern binomial naming system (Homo sapiens)