Chapter 10 Outline

How Are Genes and Proteins Related?

–The Link Between DNA and Protein
–Most Genes Contain the Informa...
Transcription and Translation
•DNA directs protein synthesis in a two-step process
•Information in a DNA gene is copied in...
mRNA
•An intermediate molecule is required to convey DNA gene sequence to the ribosome
•Messenger RNA (mRNA) performs this...
Transfer RNAs
•Transfer RNAs hook up to and bring amino acids to the ribosome
•There is at least one type of tRNA assigned...
Mutations Provide the Raw Material for Evolution
Effects of Mutations on Proteins
•Recall that mutations are changes in th...
•Mutations create new gene sequences and are the ultimate source of genetic variation
•Mutant gene sequences that are bene...
–Different mRNAs may be translated at different rates
•Gene expression is regulated in a number of ways (continued)
–Prote...
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Chapter 10 Outline

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Chapter 10 Outline

  1. 1. Chapter 10 Outline How Are Genes and Proteins Related? –The Link Between DNA and Protein –Most Genes Contain the Information for the Synthesis of a Single Protein –DNA Provides Instructions for Protein Synthesis via RNA Intermediates –Overview: Genetic Information Is Transcribed into RNA, Then Translated into Protein –The Genetic Code Uses Three Bases to Specify an Amino Acid The Link Between DNA and Protein •DNA contains the molecular blueprint of every cell •Proteins are the “molecular workers” of the cell •Proteins control cell shape, function, reproduction, and synthesis of biomolecules •The information in DNA _____ must therefore be linked to the proteins that run the cell One Gene Encodes One Protein •Synthesis of new molecules inside the cell occurs through _________ pathways •Each step in a biochemical pathway is catalyzed by a protein enzyme •George Beadle and Edward Tatum showed that one DNA gene encodes the information for one enzyme (protein) in a biochemical pathway •There are exceptions to the one gene/one protein relationship, as discussed later RNA Intermediaries •DNA in eukaryotes is kept in the ____________ •Protein synthesis occurs at ribosomes in the cytoplasm •DNA information must be carried by an intermediary (RNA) from nucleus to cytoplasm •RNA differs structurally from DNA –RNA is single stranded –RNA uses the sugar ribose –RNA uses the nitrogenous base uracil (U) instead of thymine (T) •There are three types of RNA involved in protein synthesis –_________ RNA (mRNA) carries DNA gene information to the ribosome –___________ RNA (tRNA) brings amino acids to the ribosome –Ribosomal RNA (rRNA) is part of the structure of ______________
  2. 2. Transcription and Translation •DNA directs protein synthesis in a two-step process •Information in a DNA gene is copied into mRNA in the process of transcription 2. mRNA, together with tRNA, amino acids, and a __________, synthesize a protein in the process of _____________ The Genetic Code •The base sequence in a DNA gene dictates the sequence and type of amino acids in translation •Bases in mRNA are read by the ribosome in triplets called __________ •Each codon specifies a unique amino acid in the genetic code •Each mRNA also has a __________ and a stop codon Overview of Transcription •Transcription of a DNA gene into RNA has three stages –Initiation –Elongation –Termination Initiation Initiation phase of transcription –DNA molecule is unwound and strands are separated at the beginning of the gene sequence 2. RNA polymerase binds to _____________ region at beginning of a gene on template strand Elongation Elongation phase of transcription –RNA polymerase synthesizes a sequence of RNA nucleotides along DNA template strand 2. Bases in newly synthesized RNA strand are complementary to the DNA template strand –RNA strand peels away from DNA template strand as DNA strands repair and wind up •As elongation proceeds, one end of the RNA drifts away from the DNA; RNA polymerase keeps the other end temporarily attached to the DNA template strand •Figure 10-5, p. 174, shows many RNA molecules undergoing elongation Termination Termination phase of transcription –RNA polymerase reaches a termination sequence and releases completed RNA strand
  3. 3. mRNA •An intermediate molecule is required to convey DNA gene sequence to the ribosome •Messenger RNA (mRNA) performs this function by serving as the complementary copy of a ___________gene that is read by a ribosome •In prokaryotes –The chromosomes are not contained within a nucleus –All of the nucleotides in a gene encode for the amino acids of a protein –Genes for a related function are adjacent and are transcribed together –Transcription and translation occur simultaneously within the same compartment •In eukaryotes –The DNA is in the nucleus and the ribosomes are in the cytoplasm –The genes that encode the proteins for a biochemical pathway are not clustered together on the same chromosome –Each gene consists of multiple segments of DNA that encode for protein, called _____ –Exons are interrupted by other segments that are not translated, called i__________ –Transcription of a gene produces a very long RNA strand that contains introns and exons –Enzymes in the nucleus cut out the introns and splice together the exons to make true mRNA –mRNA exits the nucleus through a membrane pore and associates with a ribosome •Why are eukaryotic genes split up into exons and introns? –Through “alternate” splicing, a cell can make multiple proteins from a single gene* –*Exception to the one gene/one protein relationship Ribosomes •_____________ are large complexes of proteins and rRNA •Ribosomes are composed of two subunits –Small subunit has binding sites for mRNA and a tRNA –Large subunit has binding sites for two tRNA molecules and catalytic site for peptide bond formation
  4. 4. Transfer RNAs •Transfer RNAs hook up to and bring amino acids to the ribosome •There is at least one type of tRNA assigned to carry each of the twenty different amino acids •Each tRNA has three exposed bases called an _______________ •The bases of the tRNA anticodon pair with an mRNA codon within a ribosome binding site Translation Ribosomes, tRNA, and mRNA cooperate in protein synthesis, which begins with initiation: –The mRNA binds to the small ribosomal subunit 2. The mRNA slides through the subunit until the first AUG (_______codon) is exposed in the first tRNA binding site… 3. The first tRNA carrying methionine (and anticodon UAC) binds to the mRNA start codon completing the initiation complex 4. The large ribosomal subunit joins the complex Middle phase of protein synthesis: Elongation (continued) –A second tRNA binds to the second tRNA binding site adjacent to the first tRNA 2. The anticodon of the second tRNA is complementary to the mRNA codon exposed in the second tRNA binding site… Middle phase of protein synthesis: Elongation 3. A peptide bond forms between the methionine and second amino acid through the action of the ribosome catalytic site –The first amino acid is released from the tRNA in the first tRNA binding site… Middle phase of protein synthesis: Elongation (continued) –The “empty” tRNA in the first binding site leaves the ribosome –The ribosome moves down the mRNA by ____________, transferring the tRNA holding the amino acid chain to the first tRNA binding site… Middle phase of protein synthesis: Elongation (continued) –A new tRNA with anticodon complementary to the newly exposed codon in the second tRNA binding site approaches and the whole elongation cycle repeats –Empty tRNAs are reloaded with their appropriate amino acids by enzymes in the cytoplasm End phase of protein synthesis: Termination –A stop codon on the mRNA slides into the second tRNA binding site –A special protein binds to the stop codon –The ribosome breaks into separate subunits… –The finished protein chain is ______________ –The mRNA is released and can be used to make another protein
  5. 5. Mutations Provide the Raw Material for Evolution Effects of Mutations on Proteins •Recall that mutations are changes in the base sequence of DNA •Most mutations are categorized as –Substitutions –Deletions –Insertions –Inversions –Translocations Effects of Mutations on Proteins •Inversions and translocations –When pieces of DNA are broken apart and ________ in different orientation or location –Not problematic if entire gene is moved –If gene is split in two it will no longer code for a complete, functional protein •Insertions or deletions –Nucleotides are added or subtracted from a gene –Reading frame of RNA codons is changed •THEDOGSAWTHECAT is changed by deletion of the letter “S” to THEDOGAWTHECAT –Resultant protein has very different amino acid sequence; almost always is non- functional •Nucleotide substitutions (____________mutations) –An incorrect nucleotide takes the place of a correct one –Protein structure and function is unchanged because many amino acids are encoded by multiple codons –Protein may have amino acid changes that are unimportant to function (neutral mutations) •Effects of nucleotide substitutions –Protein function is changed by an altered amino acid sequence (as in gly val in hemoglobin in __________________ anemia) –Protein function is destroyed because DNA mutation creates a premature stop codon Mutations Fuel Evolution •Mutations are heritable changes in the DNA •Approx. 1 in 105-106 eggs or sperm carry a mutation •Most mutations are harmful or neutral
  6. 6. •Mutations create new gene sequences and are the ultimate source of genetic variation •Mutant gene sequences that are beneficial may spread through a population and become common How Are Genes Regulated? •The human genome contains ~ ___________ genes •A given cell “expresses” (transcribes) only a small number of genes •Some genes are expressed in all cells •Other genes are expressed only –In certain types of cells –At certain times in an organism’s life –Under specific environmental conditions Gene Regulation in Prokaryotes •Prokaryotic DNA is organized into units called operons, which contain functionally related genes •Each operon consists of –A __________ gene, which controls the transcription of other genes –A _____________, which RNA polymerase recognizes as the place to start transcribing –An operator, which governs access of RNA polymerase to the promoter –The structural genes, which encode for related proteins •Whole operons are regulated as units, so that functionally related proteins are synthesized simultaneously when the need arises •The intestinal bacterium Escherichia coli (E.coli) lives on what its host eats •Specific enzymes are needed to metabolize the type of food that comes along •e.g. in newborn mammals, E.coli are bathed in milk, containing the milk sugar lactose •The __________operon contains three structural genes, each coding for an enzyme that aids in lactose metabolism; Figure 10-10, p. 181, illustrates regulation of the lactose operon… Gene Regulation in Eukaryotes •Eukaryotic gene regulation –DNA is in a membrane-bound nucleus –Variety of cell types in _______________ –The genome is organized differently –RNA transcripts undergo complex processing •Expression of genetic information by a eukaryotic cell is a multistep process, beginning with transcription of DNA, and ending with a protein that performs a particular function •Gene expression is regulated in a number of ways –The frequency of transcription of a gene can be controlled
  7. 7. –Different mRNAs may be translated at different rates •Gene expression is regulated in a number of ways (continued) –Proteins may be synthesized in an inactive form and require modification for activation –Life span of a protein can be regulated

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