Biology 10 Lecture Chapter 25 - Molecular Basis of Inheritance Roles of DNA & RNA I. Overview A. DNA Structure & Replication B. Gene Expression (DNA to RNA to Protein) C. Control of Gene Expression D. Gene Mutations II. DNA Structure & Replication A. _______ were known to be hereditary material in chromosomes in the cell nucleus by the mid-1900s. B. This hereditary material was found to be ______ (deoxyribonucleic acid) by Hershey & Chase’s experiment: 1. Labeled some T2 virus _______ coats with radioactive 35S. 2. Labeled other T2 virus ______ with radioactive 32P. 3. Incubated labeled viruses with ___________ cells. 4. Found that the labeled _____, not the protein, entered the bacteria and produced more viruses. C. Structure of ______ 1. DNA is composed of ___________ (phosphate, deoxyribose sugar, and a nitrogen 2. 3. base) DNA nitrogenous ________ include: a. ____________ have a double ring structure and include adenine (__) and guanine (__) b. ____________ have a single ring and include thymine (__) and cytosine (__) c. Chargaff found an equal amount of __________ and ____________ in DNA. d. Amount of A =__ and amount of G =___. Rosalind Franklin’s X-ray diffraction photograph showed that the DNA molecule was a double ________. D. Watson & Crick model of DNA 1. DNA consists of two strands of nucleotides, twisted together in a double 2. 3. _________, like a twisted ladder. Sugar-phosphate molecules make up the sides of the ladder, nitrogen ________ form the rungs. Base pairs are _______________: a. Purine Adenine (__) pairs with pyrimidine Thymine (__). 2 b. 4. 5. Purine Guanine (__) pairs with pyrimidine Cytosine (__). Weak ____________ bonds hold base pairs together. Linear ____________ of bases can be in any order, providing great genetic variability. E. DNA ______________ - unzipping and recoupling bases 1. During ___ stage of interphase, DNA unwinds & “unzips.” 2. Helicase unwinds DNA & breaks the ____________ bonds between base pairs. 3. _____________ in nucleoplasm are joined to complementary bases of separated, 4. 5. single DNA strands by DNA _________. Two _____________ DNA double helices result. Called semiconservative replication because each resulting double helix has one _________ strand and one ____ strand. III. _______ Expression (Protein Synthesis) A. Overview (DNA mRNA tRNA + A.A. Protein) 1. 2. 3. 4. DNA in the nucleus is like a cookbook containing _______ “recipes” for __________. DNA unwinds at a gene and the “recipe” is rewritten (______________) as messenger RNA (_____). mRNA moves from nucleus to cytoplasm and is “clamped” onto the E. R. protein assembly line by __________ (rRNA). Transfer RNA (_____) then brings appropriate amino acid “ingredients” to mRNA (___________) to make the protein. B. Structure of _____ 1. Mostly ____________-stranded, not helical. 2. Composed of nucleotides, but has ________ sugar instead of deoxyribose. 3. Thymine of DNA is replaced by _________ in RNA, thus adenine pairs with uracil in RNA. C. Three types of ______ in Protein Synthesis: 1. _____ - carries coded sequence of bases in 3 base ______ from DNA in nucleus to ribosomes in cytoplasm. 2. ______ - major component of ribosomes produced in the ________; ribosomes bind mRNA during protein synthesis 3. ______ - carries an amino acid specific for its 3 base _____________ to a complementary mRNA codon. D. The Genetic Code 1. The order of DNA bases ultimately codes for the order of _____ ________ in proteins. 3 2. The _________ code of four bases supplies 43=64 triplets, more than enough for the ___ amino acids. 3. 4. A _______ is a “3 letter” unit of 3 nucleotides in ______. 5. 61 codons correspond to particular ______ _____ (usually more than one codon per amino acid) 6. 7. Three are _______ codons (UAA, UAG, UGA). All 64 mRNA _____ have been determined, as to which ______ _______ will be brought to them (see chart) One codon (_____) for methionine is a _______ codon to begin protein synthesis. E. _______________ - first stage in protein synthesis: DNA is “transcribed” to mRNA; occurs in the ____________ 1. 2. A portion of DNA (________) unwinds and unzips. 3. 4. RNA _________ pairs with DNA adenine. 5. Processed mRNA exits nucleus through nuclear membrane pores to ____________ in cytoplasm. Complementary ______ nucleotides pair with DNA nucleotides of the sense strand, via RNA ____________. Resulting mRNA is processed by RNA ribozymes to remove ________ and leave ________ that will be expressed. F. _____________ - second stage in protein synthesis in which the sequence of mRNA nucleotide codons is “translated” into a specific sequence of amino acids brought by tRNA (in the ______) 1. 2. Initiation - ______ binds to a ribosome on the E. R. Elongation a. tRNAs with __________ complementary to mRNA _______ bring specific ______________ one at a time in the sequence dictated by mRNA. b. Each new amino acid forms a ___________ bond with the previous amino acid to form the _______________ chain. 3. Termination - Translation ends when tRNA binds to _______ codon on mRNA; ribosomes dissociate from mRNA. 4. ______________ are several ribosomes that move along mRNA at one time, for several polypeptides made at once. G. ____________ of Gene Expression 1. DNA in the nucleus contains a ________ code; each group of 3 bases corresponds to a specific amino acid 2. During ______________, a segment (gene) of DNA serves as a template for the formation of _______ (DNA mRNA) 3. mRNA carries its sequence of ________ to ribosomes in the cytoplasm 4 4. During ____________, ______ with anticodons complementary to the mRNA codons bring specific ___________ to the mRNA 5. The linear sequence of the ______ codons determines the order of amino acids in the resulting polypeptide. IV. ___________ of Gene Expression A. All cells receive the same DNA with the same _______, but cells differ as to which genes they __________ (e.g.: Muscle cells have different genes “turned on” than nerve cells) B. In __________ cells, several mechanisms regulate gene ________ from transcription to protein activity. These mechanisms include 1. In the ____________: a. Transcriptional control mechanisms during ______ transcription include the organization of chromatin and the use of transcription _________ that initiate transcription. b. Posttranscriptional control mechanisms after mRNA is formed include how mRNA is ____________ before it leaves the nucleus and the speed at which it leaves. 2. In the _____________: a. Translational control occurs before the ________ is formed; some mRNA molecules survive longer than others, thus less protein is formed. b. Posttranslational control occurs after protein synthesis; the protein may have to undergo additional _________ before it is functional. C. ______________ Control in Eukaryotes involves the organization of chromatin and regulatory proteins called transcription factors 1. 2. Organization of ____________ a. Chromosomes must ____________ before a gene can be transcribed b. In ____________ chromosomes of vertebrate egg embryos, mRNA is synthesized rapidly c. As the larvae develop, first one, then another region of the chromosomes bulge out, forming chromosome _______, where the chromosome is decondensing d. This allows RNA _________ to attach to the section of DNA Transcription factors are DNA binding __________ a. Different cell types contain different transcription ________; a specific combination is thought to regulate the activity of a particular gene b. After the right combination of transcription factors binds to DNA, an RNA ___________ attaches to the DNA and begins transcription c. As cells mature, they become ____________, determined by which ______ are active and by which transcription _______ are present 5 d. Signals received from outside and inside the cell may turn __ or ____ genes for particular transcription factors IV. Effects of Gene _____________ on Protein Synthesis A. B. C. Gene Mutation - change in the _________ sequence of a gene. _______________ Mutation 1. One or more nucleotides is ________ or _______ from DNA. 2. ___________ frame (sequence of mRNA codons) is shifted (e.g., THE CAT ATE THE RAT changed to THE ATA TET HER AT when C in CAT is deleted). 3. 4. Shifted mRNA ______ sequence leads to incorrect amino acid sequence. Usually results in nonfunctional ___________. __________ Mutation 1. 2. Change in one ________, results in a change in one ______. May have one of three ___________: a. __________ Mutation - codon is changed to codon for the _______ amino acid; no effect on protein. b. ___________ Mutation - codon is changed to a premature ______ codon; protein is too short and nonfunctional. c. _____________ Mutation - codon is changed to codon for a different _______ _____; may or may not affect protein, depending on the properties of the respective amino acids (e.g., change from polar __________ to nonpolar ______ in hemoglobin results in sickle-cell anemia) D. Cause & Repair of Mutations 1. Mutations due to DNA replication errors are very rare because DNA ___________ “proofreads” and corrects the new strand 2. __________ are environmental influences that cause mutations, such as radiation and organic chemicals 3. If mutagens cause a mutation in the ____________, then the organism’s offspring may be affected 4. If the mutation occurs in the individual’s body cells, _________ may result.