Presentation on theme: "Chapter 14 From DNA to Proteins"— Presentation transcript:
1 Chapter 14 From DNA to Proteins Honors Biology ProgramMountain Pointe High School
2 What are the byssus of a mussels? Why are these byssus so important?
3 Archibald GarrodFirst to notice that many heritable diseases were related to metabolic pathway malfunctions.STEPS OF A METABOLIC PATHWAY:Action of enzyme 1Action of enzyme 2Garrod hypothesized that each of his affected patients had inherited a single metabolic defect that interfered with an enzyme in a particular metabolic pathway.Something has interfered with the action of enzyme 3.XABCDCompletion of the pathway is blocked, and C accumulates.
4 Neurospora crassa and other fungal species Beadle & Tatum33 years after Garrod’s hypothesis, these scientists were experimenting with a common bread mold that’s capable of synthesizing everything it needs to survive except for a few basic substances.They discovered that some of the fungal strains would only grow when supplied with vitamin B6, others would only grow in the presence of B12, etc.Neurospora crassa and other fungal species
5 Beadle & TatumAfter careful examination, they discovered that there was a different defective enzyme in each mutant strain of the fungus.In other words, each strain of fungus possessed an inherited mutation that corresponded to a defective enzyme.This evidence supported Garrod’s “one gene, one enzyme” hypothesis!
6 Sickle-cell AnemiaThe most common lethal genetic disease in African Americans, it causes normal red blood cells to become sickle shaped, which causes an incredible variety of health problems for its victims.Normal red blood cellSickled red blood cell
7 Sickle-cell AnemiaIt was discovered that this disease was caused by a defect in a protein known as hemoglobin that is found in red blood cells.Normal hemoglobin is designated HbA.Abnormal hemoglobin is designated HbS.
8 glass tube or plates containing gel Pauling & Itanoupper buffer solutionmovement of proteinsIn 1949, these scientists subjected molecules of HbA and HbS to gel electrophoresis.In this procedure, an electric field is used to move molecules through a gel.Molecules are separated by their size, shape & surface charge.electrodeglass tube or plates containing gelgellower buffer solutionelectrodepower supply
9 HbS molecules moved much slower. Pauling & ItanoHbA molecules carried the greatest surface charge and therefore moved through the gel the fastest.HbS molecules moved much slower.As molecules move through the gel, they’re separated into distinct bands.
10 Vernon IngramPinpointed the biochemical difference between HbA and HbSHemoglobin (left) is a molecule made of 4 polypeptide chains, 2 alpha & 2 beta.Ingram discovered that the defect was caused by an incorrect amino acid substitution in one of the beta chains!
11 Beta chain of an HbA molecule Beta chain of an HbS molecule ```Hemoglobin moleculeBeta chain of an HbA moleculeVALINEPROLINETHREONINELEUCINEGLUTAMATEHISTIDINEGLUTAMATEBeta chain of an HbS moleculeA beta chainPROLINEVALINEVALINETHREONINEGLUTAMATEHISTIDINELEUCINE
12 The discovery of the difference between the alpha & beta chains of hemoglobin meant that… Two genes must code for hemoglobin, one for each type of polypeptide chain.Genes code for all proteins, not just enzymes.The amino acid sequences of polypeptide chains are encoded in genes.
14 The Three Types of RNAmRNA is a single-stranded molecule that takes DNA’s protein-building instructions out of the nucleus.rRNA is the primary component of ribosomes, the organelles that actually make proteins.tRNA is the molecule responsible for delivering amino acids one by one to a ribosome in the correct order specified by the mRNA molecule.A messenger RNA molecule (mRNA)A ribosomal RNA molecule (rRNA)A transfer RNA molecule (tRNA)
15 Comparing DNA and RNA Double-stranded Deoxyribose sugars 4 nitrogenous basesAdenineCytosineGuanineThymineSingle-strandedRibose sugars4 nitrogenous basesAdenineCytosineGuanineUracilLike thymine, uracil (at right, in blue) is a pyrimidine and is capable of pairing with adenine.
16 transcribed DNA winds up again Transcriptionsugar-phosphate backbone of one strandof nucleotides in a DNA double helixsugar-phosphate backbone ofthe other strand of nucleotidespart of the sequence ofbase pairs in DNATranscription is the process of using a portion of the DNA molecule as a template to assemble a molecule of mRNA.Only a selected stretch of one DNA strand is used as a template.Transcription is initiated at a promoter, a DNA base sequence that signals the start of a gene.transcribed DNA winds up againDNA to be transcribed unwindsNewly forming RNA transcriptThe DNA template at the assembly site
17 Transcriptiongrowing mRNA transcript3’5’3’5’direction of transcription3’5’A “pre mRNA” strandOnce the enzyme DNA helicase has unzipped the DNA molecule at the appropriate location…RNA polymerase adds the required complementary bases to the exposed bases on one of the DNA strands.
18 Transcription Next, the pre- mRNA molecule must be modified. unit of transcription in a DNA strandNext, the pre- mRNA molecule must be modified.A nucleotide known as a “cap” is attached to the 5` end.A nucleotide known as a “poly-A tail” is attached to the 3` end.3’5’exonintronexonintronexontranscription into pre-mRNApoly-Atailcap(snipped out)5’(snipped out)3’5’3’mature mRNA transcriptBefore the mRNA transcript is finished, useless sections known as introns must be snipped out, leaving only exons remaining.
19 Now that the mRNA has been transcribed, what does its message mean? The Genetic CodeDNA templatecodoncodoncodoncodoncodonmRNA transcriptAmino acid?Amino acid?Amino acid?Amino acid?Amino acid?
20 amino acid attachment site tRNA molecules have a nucleotide triplet known as an “anticodon” on one end and an attachment site for an amino acid on the other end.anticodoncodon in mRNAanticodontRNA MOLECULEamino acidattachment siteaminoacidamino acid attachment site
21 platform for chain assembly Ribosomes are composed of two subunits made of rRNA. These subunits are created in the nucleolus, travel separately out of the nucleus and only unite when mRNA messages need to be translated into proteins.platform for chain assemblytunnelSmall ribosomal subunitLarge ribosomal subunitComplete ribosome
22 Translation 3 Stages of Translation: Initiation tRNA molecule is attached to small ribosomal subunit.mRNA molecule’s START codon (AUG) matches up with tRNA anticodon, attaches to small ribosomal subunit.Large ribosomal subunit attaches to small subunit.
23 P (first binding site for tRNA) Binding site for mRNAP (first binding site for tRNA)A(second binding site for tRNA)
24 Translation Next is the elongation stage: Ribosome complex moves along mRNA molecule.One by one, tRNA molecules deliver the amino acids coded for by the mRNA to A site.Amino acids are linked together by peptide bonds, tRNA molecules exit P site of ribosome.
25 Translation The final stage is termination. Ribosomal complex reads STOP codon on mRNA molecule.No tRNA has an anticodon that corresponds to a STOP codon.Proteins called release factors bind to ribosome, cause enzymes to detach mRNA & polypeptide chain from ribosome.Ribosomal subunits separate.
27 Unwinding of gene regions of a DNA molecule TRANSCRIPTIONPre mRNA Transcript ProcessingmRNArRNAtRNAMature mRNA transcriptsRibosomal subunitsMature tRNATRANSLATIONCytoplasmic pools of amino acids, tRNAs, and ribosomal subunitsSynthesis of a polypeptide chain at binding sites for mRNA and tRNA on the surface of an intact ribosomeFINAL PROTEINDestined for use in cell or for transport
28 MutationsChanges in the nucleotide sequence of genes are known as mutations.The most common types of gene mutations are:Base-pair substitutions (shown at left)FrameshiftsInsertionsDeletionsoriginalbase tripletin a DNAstranda basesubstitutionwithin thetriplet (red)As DNA is replicated, proofreadingenzymes detect the mistake andmake a substitution for it:POSSIBLE OUTCOMES:OROne DNA moleculecarries the original,unmutated sequenceThe other DNAmolecule carriesa gene mutationRemember sickle-cell anemia?It’s caused by a base-pair substitution that replaces the amino acid glutamine with valine.VALINE
29 MutationsmRNA TRANSCRIPTDNA TEMPLATEARGININEGLYCINETYROSINETRYPTOPHANASPARAGINERESULTING AMINO ACID SEQUENCEALTERED mRNA MESSAGEA BASE INSERTION (RED) IN DNAARGININEGLYCINELEUCINELEUCINEGLUTAMATEALTERED AMINO ACID SEQUENCEThe example above is a frameshift mutation known as an insertion.This mutation causes DNA’s message to shift one base to the right.A deletion would cause a one-base shift to the left.