BSC2011 Final Exam Study GuideUnit I: Review• The Central Dogma: the flow of genetic information is basic to all living thingso Three entities: DNA mRNA Proteino Three processes: Replication, transcription, translation• DNA: o Genetic information is stored in the order of sequence of nucleotideso Gene: a discrete unit of hereditary information on part of a chromosomeo Genome: refers to all of an organisms genetic material in a cell• Chromosomes:o 1 chromosome = 1 long double-stranded helical DNA molecule and its bound proteins Composed of chromatins Eukaryotic chromosomes require “DNA packing” Euchromatin: loosely packed, actively transcribed DNA + proteins Heterochromatin: tightly packed, genetically inactive DNA + proteins• RNA: an “intermediary” molecule in the flow of genetic informationo Three major types of RNA: mRNA, tRNA, and rRNA• Transcription (= “gene expression”): the synthesis of mRNA using DNA as a templateo Steps: Initiation: RNA polymerase binds to promoter sequence Elongation: RNA polymerase moves along DNA template and joins RNA nucleotides Termination: the “pre-mRNA” transcript disengages from the RNA polymeraseo Processing: Capping and tailing Splicing: introns spliced out, exons get expressed• Translation: process by which transcribed mRNA in the nucleus is “decoded” into a specific protein at a ribosome in the cytoplasmo The “genetic code” – a codon codes for one amino acid The code is redundant due to 3rd base wobble The code is virtually universalo The process: Spliced mRNA binds to a ribosome in the cytoplasm The “correct” tRNA molecule binds to mRNA• Mutation: a change in the genetic material of a cello Nucleotide substitution: may or may not change the amino acid/functional protein Silent mutation: no change Missense mutation: change occurso Nucleotide indel: causes a “frameshift” mutation by altering the codon reading frame May result in a nonsense mutation: an early or no stop signal, no protein• The critical role of proteins in cells, organisms:o Types and functions: Enzymes Structural Transport Hormones Receptors Defense Storage• Cell signaling and communication:o Cells use signaling mechanisms to regulate cell activities and community with other cellso Three stages of cell signaling: Reception transduction response• Gene regulation in Eukaryotes:o Gene regulation = the control of gene expressiono Some genes have constitutive expression (always on)o Other genes can either be expressed or repressed (facultative expression)o There are various levels of control of gene expression in Eukaryoteso Control at transcription level: Signal molecules will target protein receptors on/in cells and control gene expressionUnit I (cont.): Animal Development• Cellular processes guiding embryonic development:o For a zygote (fertilized egg cell) to develop into a multicellular embryo requires: Cell division cell differentiation morphogenesis• Processes guiding (embryonic) cell differentiationo Genomic equivalence: all the different cells types in an organism have identical genomes, but they express different geneso Totipotency: the potential of a cell to differentiate into an entire organism because no genes are irreversibly turned off Evidence for totipotency:• Nuclear transplantation, reproductive cloning• Stem cells: relatively undifferentiated cells that can be induced to differentiate• Embryonic stem cells:o Can be totipotent, pluripotent (differentiate into any cell type), and multipotent (differentiate into some cell types)• Molecular processes underlying (embryonic) cell differentiation:o Determination: a process by which a cell differentiates into a particular cell type by expressing a unique set of geneso Cytoplasmic determinants (CDs): act as signal molecules that can help regulate gene expressiono Cells can also differentiate later in development via induction of cells• Fertilization (Sea Urchin development):o Acrosome: located in the head of sperm, membrane-bound vesicle containing hydrolytic enzymes for egg penetrationo The fertilization process: Contact: sperm’s acrosome releases hydrolytic enzymes to digest egg’s outer jelly coat Acrosomal reaction: sperm ejects an acrosomal process; protein receptors in egg cell membrane recognize and bind to acrosomal-process proteins Egg and sperm cell membranes fuse: egg cell membrane becomes depolarized; resulted in a fast-block to polyspermy (temporary) Cortical reaction: Wave of calcium ions from ER at sperm site stimulates release of cortical enzymes from cortical granules; fertilization envelope forms; slow-block to polyspermy (permanent) Nulcei fuse: a zygote is created with a full set of chromosomes• Cleavage (Sea Urchin development cont.):o A rapid series of mitotic cell divisions that occurs in the absence of cell growtho Morula: solid ball of cellso Blastula: hollow ball of cells Blastocoel: the hollow cavity Blastomere: each cell in blastulao For a chick egg: cleavage is at cytoplasmic disk only; contains embryonic cell mass called the blastoderm with an upper epiblast and lower hypoblasto Cleavage Summary: Sea Urchin microlecithal, holoblastic cleavage Frog mesolecithal, holoblastic cleavage Chicken macrolecithal, meroblastic cleavage• Gastrulation (“morphogenesis”, Sea Urchin development cont.):o An undifferentiated mass of embryonic cells begins to take shape A series of cell movements rearrange the position of cells in the embryoo Results in an early embryo (gastrula) that has three primary germ layers: Outer ectoderm• Skin epidermis, central and peripheral nervous system• Pituitary gland, subcutaneous glands, mammary glands• Hair, nails, teeth• Most facial and ear bones Middle mesoderm• Skeletal system (spine, ribs, limb bones)• Cartilage, connective tissue• Circulatory system (heart and blood vessels), spleen• Reproductive system (ovaries, testes)• Excretory system (kidneys)• Muscles, notochord Inner endoderm• Thyroid, thymus, pancreas, liver, tonsils• Lining of bladder and digestive and respiratory tractso Also creates a primitive gut called the archenterono Ingression: inner mesenchyme cells undergo ingression (migration) at the onset of gastrulationo Invagination: outer cells at the vegetal pole invaginate to produce the archenterono
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