Cells Cells are the fundamental units of life in all organisms Some organisms only consists of a single cell such as bacteria cid 127 Multicellular forms such as mammals are composed of billions of cells Human body may be composed of 1 trillion cells Life began in the form of single celled organisms represented today by bacteria and blue green algae Eukaryotic cells appeared about 1 2 billion years ago A Eukaryotic cell is composed of carbohydrates lipids nucleic acids and proteins Contains sub structures called organelles Nucleus a discreet unit surrounded by a thin membrane called the nuclear membrane The nucleus contains DNA RNA Nucleus is surrounded by a gel like substance called cytoplasm Protein Synthesismanufactures proteins Mitochondria produce energy and can be thought of the cells engine Enclosed within a folded membrane and contain their own distinct DNA called mitochondrial DNA mtDNA cid 127 mtDNA has the same molecular structure and function as nuclear DNA but organized differently Somatic cells make up the body tissues like muscles bones organs and the brain Ribosomes are partly composed of RNA Essential to protein synthesis Two types of cells somatic cells and gametes Gametes aka sex cells are involved in reproduction Two types of gametes egg cells produced in female ovaries Sperm cells that developed in male testes Function of sex cells is to unite with with a gamete from an individual to form a zygote cid 127 Gametes transmit genetic information from parent to offspring The Structure of DNA DNA directs directs all cellular activities 1953 James Watson developed functional model of DNA DNA molecule composed of two chains of smaller units called nucleotides A nucleotide is made up of three components sugar a phosphate group and one of four nitrogenous bases Nucleotides stacked to form chain bonded by its bases to another nucleotide chain and forms a double helix Four DNA bases are adenine guanine thymine and cytosine Adenine can only pair with thymine A T Guanine can only pair with cytosine G C This is specificity is essential for DNAs ability to replicate make a copy of itself DNA Replication Cells multiply by dividing to make exact copies of themselves Enables organisms to grow and heal injured tissues Two kinds of cell division A cell cannot function without right amount of DNA A cell must replicate before it divides A cell divides ones time to produce two daughter cells and each receive a full set of genetic material Replication begins when enzymes break the bonds between bases throughout the DNA molecule Separates the two previously joined strands of nucleotides and leaves their bases exposed The exposed bases then attract unattached DNA nucelotides that have been made by DNA else where in the cell nucleus The attraction between exclusive base pairs is complementary I e T only with A Protein Synthesis Protein Synthesis An important activity of DNA is to direct the assembly of proteins within cells Proteins function through their ability to find to other molecules Hemoglobin is found in red blood cells and is able to bind to oxygen which it carries to cells throughout the body Collagen is a protein that are structural components of tissues Enzymes are also proteins which regulate chemical reactions Hormones are another class of proteins Released in bloodstream cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Insulin is a hormone produced by cells in the pancreas but functions in the liver where it causes cells in liver to absorb energy producing glucose from the blood cid 127 Many kinds of proteins can enter a cells nucleus and attach directly to its DNA cid 127 When the protein bind to DNA it can regulate it s activity Proteins are made up of chains of smaller molecules called amino acids There are 20 amino acids 8 amino acids must he obtained from food Remaining 12 are produced in cells DNA is the recipe for making protein Protein synthesis takes place in the cytoplasm at the ribosomes The DNA molecule cannot leave the cells nucleus into the cytoplasm RNA Is similar to DNA but differs by It s single stranded Contains different type of sugar Contains uracil instead of DNA base thymine template n The formation of mRNA is called transcription The 20 amino acids are combined in different amounts and sequences to produce at least 90 000 different proteins Therefore the first step in P S is to copy the DNA message into a form of RNA called messenger RNA which can pass through the nuclear membrane As in DNA replication the two DNA strands separate partially and one strand attracts free floating RNA nucleotides which are joined together on the DNA Transcription continues until a section or DNA called terminator region is reached and the process stops At this point the mRNA strand peels away from the DNA model A portion of it travels through the nuclear membrane to the ribosome Then the bonds between the DNA bases are reestablished and the DNA molecule becomes intact again The mRNA strand arrives at the ribosome and it s message is translated decoded cid 127 mRNA triplets are called codons Transfer RNA tRNA brings each amino acid to the ribosome The ribosome joins that amino acid to another amino acid in the order dictated by the sequence of mRNA codons What is a Gene cid 127 Gene a segment of DNA that specifies the sequence of amino acids in a particular protein DNA codes for protein RNA and DNA nucleotides Humans have only about 21 000 genes Produce as many as 90 000 proteins Exons are expressed Transcribed into mRNA Noncoding DNA does not direct production of proteins but they produce thousands of molecules RNA Introns initially transcribed into mRNA and then clipped out Not translated into amino acid sequences Regulatory Genes Regulatory genes genes that influence the activity of other genes They make various kinds of RNA proteins and other molecules that switch other DNA segments genes on or off Plays a role in embryonic development cellular function abs evolution Homeobox genes directs the segment of the overall body plan and the segmentation of body tissues Mutation When Genes Change Normal adult hemogoblin are made up of four amino acid chains 2 alpha and 2 beta that are direct products of