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Biology 121 Chapter 6

by: Maria Luisa Cepeda

Biology 121 Chapter 6 121

Maria Luisa Cepeda
University of Louisiana at Lafayette
GPA 4.0

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These notes cover the material on chapter 6.
Biology of Organisms 1
Dr. Jeffrey Spring
Study Guide
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This 11 page Study Guide was uploaded by Maria Luisa Cepeda on Wednesday February 10, 2016. The Study Guide belongs to 121 at University of Louisiana at Lafayette taught by Dr. Jeffrey Spring in Fall 2015. Since its upload, it has received 49 views.

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Date Created: 02/10/16
Chapter 6: DNA: The Molecule of Life 6.1- DNA is a polymer of nucleotides DNA is a polymer because it is a large molecules made by repeating smaller units (nucleotides)  Deoxyribonucleic Acid usually exists as one or more long fibers called chromosomes, which contain genes.  Specific stretches of DNA encode instructions for building proteins  The Double Helix  2 strands wrapped around each other.  In center of double helix, H-bonds between bases hold the 2 strands together  Nucleotides  Each molecule of DNA is made from individual subunits called nucleotides  Each contains 3 parts: a central 5-carbon sugar (deoxyribose in DNA), a negatively charged phosphate, and a base made from 1 or 2 rings of nitrogen and carbon.  Sugar + Phosphate are identical among all DNA nucleotides  DNA basses come in 4 types  A,G, T, and C  Polynucleotide  1 molecule of DNA contains 2 polynucleotides wrapped around each other  Long strand of individual nucleotides  Contains any combination of the 4 bases along its length  Sugar-Phosphate Backbone  A polynucleotide consists of bases attached to a sugar- phosphate backbone.  Alternating sugar and phosphate groups  Base Pairs  Each nucleotide contains one of four different bases: adenine, guanine, cytosine, or thymine.  Each base can form H-bonds w/ only 1 other kind of base  A with T, and C with G.  H-bonds within base pairs hold the 2 strands of the double helix together  The sequence of nucleotides along one polynucleotide within a double helix dictates the identity of nucleotides along the other polynucleotide.  A molecule of DNA is a double helix made of two intertwined polynucleotide strands. Each strand is a long string of nucleotides. Each nucleotide consists of the same sugar and phosphate, and one of four possible bases. 6.2- During DNA replication, a cell duplicates its chromosomes - If you know the base sequence of one strand, you can figure out the base sequence in the other strand by applying base-pairing rules.  Semi-Conservative Replication  During DNA Replication: 2 strands of an original DNA molecule separate from each other.  Each separated strand is a template to rebuild the other strand  End result: 2 new DNA molecules each containing 1 newly created strand and 1 strand from the original molecule.  DNA replication is said to be semi-conservative b/c each new molecule conserves half of the original molecule.  The Process of DNA Replication - Process accomplished by a series of enzymes that work together to duplicate a DNA molecule.  1. Double helix is peeled apart  Enzyme called helicase attaches to specific DNA sequences. It peels apart the 2 DNA strands  2. New strands are synthesized  Enzyme DNA polymerase builds a new DNA molecule that is complementary to the existing strand.  3. DNA fragments are fused together  DNA polymerase creates the new molecule in fragments  Enzyme called DNA ligase joins the individual fragments fusing them into the final DNA molecule 6.3- DNA directs the production of proteins via RNA - RNA directed by DNA, carries instructions to build proteins.  Nucleic Acids: DNA and RNA  Both are polymers of nucleotides  Phosphate groups are identical between DNA and RNA  3 important structural differences  1. RNA often found as a single-stranded molecule, while DNA is double stranded.  2. The sugar in DNA is deoxyribose and the one in RNA is ribose.  3. Each DNA nucleotide has one of four possible bases: A, T, C, and G. RNA nucleotides share A,C, and G bases but have Uracil instead of T.  The Flow of Genetic Information  DNA can act as molecule of heredity because it can direct protein production  First it directs production of RNA, which in turn controls the making of proteins.  DNA makes RNA, which makes proteins. 6.4- Genetic information flows from DNA to RNA to protein -DNA itself does not produce your appearance. Rather DNA directs production of proteins, which are responsible for your physical traits.  Transcription  Info in a DNA gene is converted to an RNA molecule in nucleus.  The molecule that DNA makes is messenger RNA.  Transcription follows base-pairing rules (C transcribed to G, but an A nucleotide in DNA is transcribed to a U nucleotide in RNA)  Uracil is used in RNA instead of Thymine  mRNA leaves the nucleus and travels to ribosomes for translation .  Translation  RNA makes its way to the ribosomes where the message is converted to protein.  Sequence of RNA nucleotides on a molecule of mRNA serves as instructions to build an amino acid sequence.  A molecule of mRNA contains successive codons  Codons are sequences of 3 nucleotides. Each specifies for 1 amino acid  Within cytoplasm, ribosomes read each successive codon and attach the proper amino acid to a growing chain.  Molecule that results: polypeptide, consisting if amino acids string.  Genetic info flows from DNA to messenger RNA in nucleus through process of transcription. At the ribosomes in the cytoplasm, each mRNA codon is translated into an amino acid of a protein. 6.5- Transcription creates a molecule of RNA from a molecule of DNA -Transcription: the transfer of info from DNA to a molecule of mRNA. 1. RNA polymerase binds a promoter  Enzyme binds to a DNA sequence called a promoter o It is a “start here” signal o Plays a key role in regulating genes o Cell can turn on/off genescontrolling whether RNA polymerase can bind the promoter 2. RNA polymerase synthesizes a molecule of RNA  RNA polymerase peels open the double helix o 1 strand serves as template for formation of RNA, the other is unused. o Enzyme moves down the DNA, creating a new RNA molecule one nucleotide at a time.  Transcription ends when RNA polymerase reaches “DNA stop sequence” 3. RNA splicing  Introns- regions that do not encode for amino acids are removed  Regions that code for amino acids called exons are splice (joined) together. 4. mRNA leaves the nucleus  mRNA leaves through nuclear pores. 6.6- Translation involves the coordination of three kinds of RNA -Translation: process by which a molecule of mRNA is used to produce a molecule of protein. Takes place in cytoplasm in ribosomes. -Molecules of transfer RNA translate triplets of RNA nucleotides into amino acids using a specific genetic code.  Ribosomes  Made from proteins combined with a type of RNA, called ribosomal RNA.  Within each ribosomebinding sites for mRNA and molecules of transfer RNA.  Ribosome can read the mRNA three nucleotides at a time. Each set of three, a codon, encodes one of 20 amino acids.  Transfer RNAs  tRNAs can speak “the RNA language” through a structure called anticodon.  On one end of tRNA: anticodon binds to codon of a mRNA via the RNA base-pairing rules (A with U, C with G..)  On other end of the tRNA: holds the amino acid that corresponds to that codon.  The Genetic Code  Triplet code  3 consecuve RNA bases, a codon that encodes for one amino acid. 6.7- Translation creates a molecule of protein via the genetic code 1. Initiation: Ribosome assembles  2 subunits of ribosome attach to mRNA  A tRNA brings in amino acids that match the codon in the mRNA 2. Elongation: Polypeptide grows longer  Continues until ribosome reaches a stop codon on the mRNA 3. Termination: Ribosome disassembles  Ribosome machinery disassembles  Completed polypeptide can now me modified into functional protein. 6.8- Gene expression is regulated in several ways  Gene regulation  Mechanisms that turn genes on and off.  Some genes are turned on in some cells and not in others.  X Chromosome Inactivation  In females 1 X chromosome inn each body cell is highly compacted by proteins and almost inactive.  Ensures that males (who have only 1 x chromosome) and females (who have 2) have the same number of active genes.  Several points along the path from DNA to RNA to protein that can be regulated  1. Special Transcription Factors  A series of proteins called transcription factors  Must bind to DNA before transcription can begin  2. Control of RNA  Before leaving nucleus :RNA transcribed from gene can be altered in many ways  Cap and tail are added  Noncoding regions introns may be removed  Protein-coding regions extrons may be rearranged  Cell can control whether translation proceeds, how proteins are modified after translation, and when proteins are broken down. 6.9- Signal Transduction pathways can control gene expression -Cell to cell communication  The binding of a molecule produced by a cell to a receptor protein on the outside of another cell triggers a signal transduction pathway  Series of proteins pass on the message from outside the cell into cell’s interior cytoplasm and eventually to nucleus.  The result: signal usually causes the turn on or off of 1 or more genes  New protein may be made as a result of the signal  Cell-to-Cell Signaling in a Developing Embryo  Development (from embryo into an adult)  Involves frequent cell division to increase body size that must be coordinated  To control formation of organs and organization of body, chemical signals are passed between neighboring cells.  Induction  These signals can cause cells to change shape, migrate or even to destroy other cells (ex: developing hand)  Homeotic genes  Master control genes help establish overall structure of an organism (the location of body parts) 6.10-Mutations can have a wide range of effects  Mutationany change in the nucleotide sequence of DNA. Some are helpful but most are harmful.  DNA polymerase makes roughly 1 mistake per 10,000 base pairs  Error rate reduced to 1 mistake per billion base pairs due to proofreading enzymes.  Can be spontaneous or caused by mutagens  Physical or chemical factors in the environment that can damage DNA:  Many mutagens are carcinogens: UV radiation, chemicals, etc.  Point Mutations: substitution of one DNA nucleotide for another  Silent: doesn’t change amino acid produced so protein is unchanged  Missense: substitutes one amino acid for another producing mutant protein (can be identical or different from the original)  Nonsense: changes amino acid codon to a stop codon producing a shortened protein (defective)  Frameshift mutations  Mutations that add nucleotides (insertions) or remove them (deletions) may alter the triplet reading frame of codons. 6.11-Loss of gene expression control can result in cancer Gene expression- flow of genetic info from DNA to RNA to protein  Cell will sometimes lose ability to control its cell cycle  Result is tumor: a mass of body cells that is growing out of control  If it can spread to other tissuescancer  Result from mutations in genes that regulate cell cycle  Cell Control System: within each cell regulates the timing of cell duplication  A mutation in one of the genes may produce a faulty protein.  Proto-oncogene: normal, necessary gene that produces a protein that properly regulates cell cycle  Oncogene: mutated pro-oncogene that produces an abnormal protein that fails to regulate cell cycle. Result is out of control growth.  Growth Factor  Normal protein that stimulates cell division  A mutation in a growth factor gene protein that promotes cell division when it should nottumor may result.  Tumor Suppressor Genes  Normally code for proteins that inhibit cell division  A mutation deactivates gene causing uncontrolled growth 6.12-Cancer is caused by out-of-control cell growth - Cancer begins within a single cell when proto-oncogens mutate into oncogens.  Treatment: “slash, burn and poison” surgery, radiation and chemo. 6.13- Genetic engineering involves manipulating DNA for practical purposes  Learning about structure and function of DNA led to development of technologies:  Biotechnology:  DNA technology  Genetic engineering : pharmaceutical products (insulin)  Gene cloning  The gene that synthesizes a protein is isolated and inserted into a piece of bacterial DNA called a plasmid. As bacteria multiply, large amounts of the gene and the protein are produced.  Restriction enzymes  Proteins that cut DNA at specific nucleotide sequences 6.14-DNA may be manipulated many ways within the laboratory  Genomic Library: collection of cloned DNA fragments that includes an organism’s entire genome.  Nucleic Acid Probes: complementary molecule made using radioactive or fluorescent blocks that will bind to DNA.  DNA synthesized from scratch automated DNA synthesizer. Customized DNA molecules up to few hundred nucleotides long.  DNA produced from a cell’s RNA  Reverse transcriptase is the enzyme that can build DNA molecules from collection of mRNAs within cell.  The result complementary DNA 6.15- Plants and animals can be genetically modified  GMOs- are organism that have acquired one or more genes by artificial means.  Transgenic organism: gene acquired from another species (ex: goat carrying human gene)  Transgenic Crops  Currently GMOs make up a significant part of our food supply  Bt Corn(expresses protein that acts as insecticide), golden rice (Beta-carotene), Hawaii papaya resistant to virus  Transgenic Animals  Not part of our food supply yet 6.16- PCR can be used to multiply DNA Samples  Polymerase Chain Reaction (PCR)  Lab technique by which a specific DNA segment can be copied quickly and precisely.  Heating splits apart DNA into two strands.  DNA polymerase is used to build each missing strand  Primers: short single DNA strands that bind to the start and end points of the segment of DNA being amplified. 6.17-DNA profiles are based on STR analysis  DNA profiling- set of lab techniques that lets you determine with certainty whether two samples of DNA cam from same individual.  comparing the sequences of the entire set of DNA in each sample is impractical.  Instead DNA profiling compares specific sites of DNA within the genome that are known to vary among the population.  Short Tandem Repeats (STRs)  At each STR site, a 4-nucleotide sequence is repeated many times in a row. (# of repeats varies widely among the human population)  STR Analysis current method for generating DNA profile relies on it.  A comparison of the lengths of short tandem repeats sequences at 13 sites within human genome.  No humans have ever had the same # of repeats at all 13 sites (Except identical twins)  Gel Electrophoresis  Allows visualization of DNA samples based on their length. 6.18-Whole genomes can be sequenced and mapped - 2003 researches announced they had sequenced all genes from a human -Found that out chromosomes contain about 21,000 genes -Genome of two humans of same sex is about 99.5% identical -only 1.5 % of human DNA encodes for proteins -59% of the human DNA is repetitive  Genome mapping includes several techniqueswhole-genome shotgun method  Proteomics- examining the complete set of proteins encoded by a genome.


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