* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 12
Maurice Wilkins wikipedia , lookup
Community fingerprinting wikipedia , lookup
RNA silencing wikipedia , lookup
Gel electrophoresis of nucleic acids wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Polyadenylation wikipedia , lookup
Molecular cloning wikipedia , lookup
Biochemistry wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
DNA supercoil wikipedia , lookup
Expanded genetic code wikipedia , lookup
Messenger RNA wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Non-coding DNA wikipedia , lookup
Molecular evolution wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Non-coding RNA wikipedia , lookup
Point mutation wikipedia , lookup
Gene expression wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genetic code wikipedia , lookup
Epitranscriptome wikipedia , lookup
Molecular Biology of the Gene DNA Structure and Function History of DNA • 1869 Johann Friedrich Miescher • 1924 Microscope studies using stains for DNA and protein show that both substances are present in chromosomes. • 1952 Alfred Hershey and Martha Chase SCIENTIFIC DISCOVERY: DNA is a double-stranded helix Erwin Chargaff Rosalind Franklin / Maurice Wilkins James Watson and Francis Crick In 1962, the Nobel Prize SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material Until the 1940s, the case for proteins serving as the genetic material was stronger than the case for DNA. – Proteins are made from ____different amino acids. – DNA was known to be made from just ____ kinds of nucleotides. Studies of bacteria and viruses – ushered in the field of molecular biology, the study of heredity at the molecular level, and – revealed the role of DNA in heredity. DNA and RNA are polymers of nucleotides DNA and RNA are nucleic acids. The building blocks or monomers of nucleic acids are ____________________ A nucleotide is composed of a – _________________ – _________________ – __________________ The nucleotides are joined to one another by a bond creating the sugar-phosphate backbone. T A C T G Sugar-phosphate backbone A C G T A C G A G T Covalent bond joining nucleotides T C A C A C A A G T Phosphate group Nitrogenous base Nitrogenous base (can be A, G, C, or T) Sugar C G T A A DNA double helix DNA nucleotide T Thymine (T) T Phosphate group G G G G Sugar (deoxyribose) DNA nucleotide Two representations of a DNA polynucleotide 4 Different Types of Nucleotides Found in DNA Hydrogen bond Base pair Ribbon model Partial chemical structure Computer model 3’ and 5’ ends of nucleotide strand Purine or pyrimidine ? Hydrogen bonds hold the 2 strands together 2 General Functions for DNA 1. 2. DNA replication depends on specific base pairing In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism. DNA replication follows a semiconservative model. DNA Replication SEMICONSERVATIVE 1. Helix unwinds 2. 2 strands separate 3. Free nucleotides bind to open bases according to pairing rules (parent strand acts as template) 4. 2 identical strands consist of one parent strand and one newly formed strand. DNA replication proceeds in two directions at many sites simultaneously DNA replication begins at the origins of replication where – DNA unwinds at the origin to produce a “bubble,” – replication proceeds in both directions from the origin, and – replication ends when products from the bubbles merge with each other. DNA replication occurs in the 5 to 3 direction. – Replication is continuous on the 3 to 5 template. – Replication is discontinuous on the 5 to 3 template, forming short segments. Leading and Lagging strands Why? DNA polymerases can only assemble new strands in the 5’-> 3’ direction, need a 3’ end (-OH) provided by RNA primer. DNA polymerase molecule 5 3 Parental DNA Replication fork 5 3 DNA ligase Overall direction of replication 3 5 This daughter strand is synthesized continuously This daughter strand is 3 synthesized 5 in pieces DNA replication proceeds in two directions at many sites simultaneously Key proteins are involved in DNA replication. – Helicase – DNA Polymerases– Primase – Proofreader – DNA ligase Parental DNA molecule Origin of replication “Bubble” Two daughter DNA molecules Parental strand Daughter strand ANIMATION…Replication http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf http://207.207.4.198/pub/flash/24/menu.swf http://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html DNA Repair DNA processes • Replication • Protein Synthesis –Transcription –Translation Protein Functions…. • • • • • Metabolism (enzymes are proteins) Structural (build form) Transport (ex- hemoglobin) Protection (antibodies are proteins) Cell communication (hormones) Review of Protein Structure… Only 20 different common amino acids Hundreds of thousands of different proteins ! Structure determines function ! The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits DNA specifies traits by dictating protein synthesis. The molecular chain of command is from – DNA in the nucleus to RNA and – RNA in the cytoplasm to protein. __________________ is the synthesis of RNA under the direction of DNA. __________________ is the synthesis of proteins under the direction of RNA. Nucleotides: 2 types DNA & RNA 3 parts of RNA (the other nucleic acid) nucleotide sugar = _________ phosphate group nitrogenous base (A,U,C,G) U=Uracil 3 Types of RNA Required for Protein Synthesis • mRNA= messenger RNA • tRNA= transfer RNA • rRNA= ribosomal RNA DNA Transcription RNA NUCLEUS Translation Protein CYTOPLASM Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription RNA A U G A A G U U U U A G Translation Start codon Polypeptide Met Stop codon Lys Phe The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits The connections between genes and proteins – The initial one gene–one enzyme hypothesis was based on studies of inherited metabolic diseases. – The one gene–one enzyme hypothesis was expanded to include all proteins. – Most recently, the one gene–one polypeptide hypothesis recognizes that some proteins are composed of multiple polypeptides. Transcription- overview Transcribing (writing) information from DNA Takes place in the nucleus Promoter region is recognized by RNA polymerase as a start location Assembles mRNA strand mRNA TRANSCRIPTION Free RNA nucleotides RNA polymerase C C A A A U C C A T A G G T Direction of transcription Newly made RNA T Template strand of DNA RNA polymerase DNA of gene Terminator DNA Promoter DNA 1 Initiation 2 Elongation Area shown in Figure 10.9A 3 Termination Growing RNA Completed RNA RNA polymerase Genetic information written in codons is translated into amino acid sequences The sequence of nucleotides in DNA provides a code for constructing a protein. Transcription produces genetic messages in the form of RNA Overview of transcription – An RNA molecule is transcribed from a DNA template by a process that resembles the synthesis of a DNA strand during DNA replication. – RNA nucleotides are linked by the transcription enzyme RNA polymerase. – Specific sequences of nucleotides along the DNA mark where transcription begins and ends. – The “start transcribing” signal is a nucleotide sequence called a promoter. Transcription produces genetic messages in the form of RNA – Transcription begins with initiation, as the RNA polymerase attaches to the promoter. – During the second phase, elongation, the RNA grows longer. – As the RNA peels away, the DNA strands rejoin. – Finally, in the third phase, termination, the RNA polymerase reaches a sequence of bases in the DNA template called a terminator, which signals the end of the gene. – The polymerase molecule now detaches from the RNA molecule and the gene. POST-TRANSCRIPTIONAL Exon Intron MODIFICATION Exon Intron Exon DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM Post-Transcriptional Modification: Eukaryotic RNA is processed before leaving the nucleus as mRNA Eukaryotic mRNA – RNA splicing – Additions- cap and tail Post-Transcriptional Modification: Eukaryotic RNA is processed before leaving the nucleus as mRNA Messenger RNA (mRNA) – encodes amino acid sequences and – conveys genetic messages from DNA to the translation machinery of the cell, which in – prokaryotes, occurs in the same place that mRNA is made, but in – eukaryotes, mRNA must exit the nucleus via nuclear pores to enter the cytoplasm. – Eukaryotic mRNA has – introns, interrupting sequences that separate – exons, the coding regions. Genetic information written in codons is translated into amino acid sequences The flow of information from gene to protein is based on a triplet code: the genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of nonoverlapping three-base “words” called codons. Each amino acid is specified by a codon. – 64 codons are possible. – Some amino acids have more than one possible codon. Transfer RNA molecules serve as interpreters during translation Transfer RNA (tRNA) Ribosomes build polypeptides rRNA and proteins make up the ribosome. Translation occurs on the surface of the ribosome The genetic code dictates how codons are translated into amino acids Characteristics of the genetic code – _______ nucleotides specify one amino acid. – 61 codons correspond to amino acids. – AUG is the start codon; codes for methionine and signals the start of transcription. – 3 “stop” codons signal the end of translation; _____, ____, ____ – __________- with more than one codon for some amino acids – _______________- the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals GENETIC CODE Practice • • • • DNA is TACAGGCGATGGATT mRNA is ____________________ Divide into codons (reading frames) Amino acids coded for are: An initiation codon marks the start of an mRNA message (Initiation) Translation can be divided into the same three phases as transcription: 1. initiation, 2. elongation, and 3. termination. Initiation brings together… An initiation codon marks the start of an mRNA message (Initiation) Initiation establishes where translation will begin. Initiation occurs in two steps. 1. An mRNA molecule binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon. – The start codon reads AUG and codes for methionine. – The first tRNA has the anticodon UAC. 2. A large ribosomal subunit joins the small subunit, allowing the ribosome to function. – The first tRNA occupies the P site, which will hold the growing peptide chain. – The A site is available to receive the next tRNA. Elongation adds amino acids to the polypeptide chain Once initiation is complete, amino acids are added one by one to the first amino acid. Elongation is the addition of amino acids to the polypeptide chain. Elongation adds amino acids to the polypeptide chain Each cycle of elongation has three steps. 1. Codon recognition: The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome. 2. Peptide bond formation: The new amino acid is joined to the chain. 3. Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site. Polypeptide Elongation P site mRNA Amino acid A site Anticodon Codons 1 Codon recognition mRNA movement Stop codon 2 New peptide bond 3 Translocation Peptide bond formation Elongation adds amino acids to the polypeptide chain until a stop codon; Termination Termination stage of translation, when – the ribosome reaches a stop codon, – the completed polypeptide is freed from the last tRNA, and – the ribosome splits back into its separate subunits. Other Helpful Animations…. http://highered.mcgraw-hill.com/sites (there are selections at this site that will help with replication, transcription and translation) Review: The flow of Genetic information in the cell is DNA RNA Transcription DNA 1 mRNA Transcription RNA polymerase CYTOPLASM Translation Amino acid Amino acid attachment 2 Enzyme tRNA ATP Anticodon Initiator tRNA Large ribosomal subunit Start Codon mRNA Protein Initiation of polypeptide synthesis 3 Small ribosomal subunit New peptide bond forming Growing polypeptide 4 Elongation Codons mRNA Polypeptide 5 Stop codon Termination Mutations can change the meaning of genes A mutation is any change in the nucleotide sequence of DNA. Mutations can involve – large chromosomal regions or – just a single nucleotide pair. Mutations can be spontaneous (mistakes during replication) or caused by mutagens. Examples- UV light, chemicals Mutations can change the meaning of genes . A mutation can be: – Harmful, giving rise to cancers. – Cause genetic disorders (if in sperm or egg) – Create new traits/variation in the species Normal hemoglobin DNA C T Mutant hemoglobin DNA C A T T mRNA mRNA G A A G U A Normal hemoglobin Sickle-cell hemoglobin Val Glu Normal gene mRNA Protein Nucleotide substitution A U G A A G U Met A U G A Met Lys U U G G C G C Phe Gly Ala U A G C A G U U Lys Phe Ser G C A A Ala U Deleted Nucleotide deletion A U G A A G Met U U G G C G Ala Leu Lys C A U His Inserted Nucleotide insertion A U G A A G Met Lys U U G Leu U G G C G C Ala His You should now be able to 1. Compare the structures of DNA and RNA. 2. State the contributions of Chargaff, Franklin, Wilkins, Watson and Crick to our understanding of DNA. 3. Describe the process of DNA replication. State the role of helicase, DNA polymerases, primase, and DNA ligase 4. Describe the general purpose of protein synthesis; relate DNA sequence to the specific protein produced. You should now be able to 5. State the general flow of genetic information as genes are expressed. 6. Explain transcription and how mRNA is produced using DNA. 7. Explain how eukaryotic RNA is processed before leaving the nucleus. 8. Discuss the role of mRNA, tRNA and rRNA in translation. 9. Explain translation; initiation, elongation, translocation and termination. You should now be able to 10. Describe the structure and function of ribosomes 11. .Define mutation, causes of mutations, and potential consequences. 12. State the amino acid sequence in a polypeptide given the mRNA. © 2012 Pearson Education, Inc. DNA is a polymer made from monomers called is performed by an enzyme called (b) (a) (c) (d) RNA comes in three kinds called (e) (f) (g) is performed by structures called Protein molecules are components of use amino-acid-bearing molecules called (h) one or more polymers made from monomers called (i)