March 26, 2012 NUCLEIC ACIDS AND PROTEIN SYNTHESIS

Transcription

1 NUCLEIC ACIDS AND PROTEIN SYNTHESIS

2 MAIN MAIN TOPICS TOPICS TO TO BE BE COVERED COVERED THIS THIS UNIT: UNIT: I. I. EVIDENCE EVIDENCE OF OF DNA DNA AS AS THE THE GENETIC GENETIC CODE CODE II. II. DNA DNA STRUCTURE STRUCTURE AND AND FUNCTION FUNCTION III. III. DNA DNA REPLICATION REPLICATION IV. IV. RNA RNA V. V. PROTEIN PROTEIN SYNTHESIS SYNTHESIS

3 Before we begin, a little review and introduction..

4 DNA IS THE GENETIC CODE The genetic code is the way in which cells store the program that they seem to pass from one generation of an organism to another.

5 EVIDENCE OF DNA AS THE GENETIC CODE EXPERIMENTS 1. (1928) Griffith: Transformation 2. (1952) Hershey & Chase: Bacteriophages

6 SUMMARY OF GRIFFITH S EXPERIMENT Isolated 2 different strains of pneumonia bacteria (disease causing strain and a harmless strain) from mice and injected into mice Griffith cultured disease causing cells, heated the cells to kill them, and injected mice mice lived He mixed heat-killed disease causing cells with harmless bacteria, and injected mice mice developed pneumonia and died Heat-killed bacteria passed their disease-causing ability to harmless strain - called this transformation (one strain had been transformed into another) Griffith s Hypothesis: a factor was transferred from the heat-killed bacteria to harmless bacteria, and since the ability to cause disease was inherited by the transformed bacteria s offspring, that factor might be a gene

7 GRIFFITH S EXPERIMENTS: TRANSFORMATION Sick Bacteria Sick Bacteria Healthy Bacteria Heat Killed Sick Bacteria Heat Killed Sick Bacteria + Healthy Bacteria

8 HERSHEY & CHASE BACTERIOPHAGE: virus that infects bacteria and is made of a DNA or RNA core and a protein coat

9 SUMMARY OF HERSHEY-CHASE EXPERIMENT Hershey/Chase wanted to determined which part of the bacteriophage (the protein coat or nucleic acid core) entered the infected cell They thought this would allow them to learn whether genes are made of protein or DNA They grew viruses in cultures containing 32 P and 35 S If 35 S was found in the bacteria, then protein coat was injected into the bacteria If 32 P was found in bacteria, then DNA had been injected Results: all radioactivity in bacteria was from 32 P Conclusion: the genetic material of bacteriophage was DNA, not protein

10 HERSHEY & CHASE: BACTERIOPHAGES March 26, 2012

11 Hershey & Chase Animation /120076/bio21.swf::Hershey%20and%20Chase%20Experiment

12 DNA STRUCTURE & FUNCTION THE BUILDING BLOCKS OF DNA DNA STRUCTURE DNA REPLICATION PROTEIN SYNTHESIS

13 DNA STRUCTURE & FUNCTION THE BUILDING BLOCKS OF DNA (deoxyribonucleic acid) 1. DNA is a polymer made up of nucleotides. a) A nucleotide monomer has 3 parts: 1. A 5-C sugar called deoxyribose Deoxyribose is a pentose, b/c it has 5 carbons 2. A phosphate group 3. 1 of 4 nitrogenous bases 2. Four different nitrogenous bases can be found in DNA. These bases can be two forms, either purines or pyrimidines a) Purines (bigger bases - 2 rings): Adenine (A) & Guanine (G) b) Pyrimidines (smaller - 1 ring): Thymine (T) & Cytosine (C) HINT: GA is a bigger state than CT - bigger state=bigger bases!

14 NUCLEOTIDE March 26, 2012

15 TYPES OF NUCLEOTIDES Purines (2 rings) Pyrimidines (1 ring)

16 DNA STRUCTURE & FUNCTION THE BUILDING BLOCKS OF DNA (cont.) 3. Nucleotides join together when covalent bonds form between the sugars and phosphates of the nucleotides. This forms the sugar-phosphate backbone of the DNA molecule. 4. The bases are bonded to the sugars in the nucleotides. 5. Bases of nucleotides are held to each other by weak hydrogen bonds.

17 DNA MOLECULE Nucleotide Hydrogen Bonds Sugar/Phosphate Backbone Adenine A Thymine T Cytosine C Guanine G

18 DNA STRUCTURE & FUNCTION DNA STRUCTURE 1. Evidence of DNA s Structure: a) (1950) Franklin & Wilkins: X-Ray Crystallography (Helical Shape) b) (1953) Watson & Crick: Double Helix Model & Complementary Base Pairing

19 Rosalind Franklin & X-Ray Crystallography March 26, 2012

20 Watson, Crick & the Double Helix

21 DNA STRUCTURE & FUNCTION DNA STRUCTURE (cont.) 2. DNA is a double helix (twisted ladder). There are 2 strands of DNA in each double helix. a) Each strand has a backbone of alternating sugars and phosphates. Backbones of sugar and phosphate are connected to each other at the bases by complementary base pairing.

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23 DNA STRUCTURE & FUNCTION DNA STRUCTURE (cont.) 3. Complementary base pairing is the specific attraction between certain bases. Purines (G and A) bond to pyrimidines (C and T). a) Adenine (A) always bonds to Thymine (T). b) Cytosine (C) always bonds to Guanine (G). CHARGAFF S RULE: the # of adenine = # of thymine # of cytosine = # of guanine 4. Therefore, the bases of one strand of DNA determine the bases of the other strand.

24 Hmmm If you have a DNA molecule with 120 bases, and 20 of those bases are adenine, how many thymine, guanine and cytosine are there?

25 COMPLEMENTARY BASE PAIRING IN DNA What is the matching strand? AATGCGATA

26 CHROMOSOMES AND DNA REPLICATION DNA and Chromosomes: Prokaryotic cells DNA molecules are located in the cytoplasm most have a single circular DNA molecule that contains nearly all of the cell s genetic info

27 CHROMOSOMES AND DNA REPLICATION DNA and Chromosomes: Eukaryotic Cells - DNA is in the nucleus in the form of chromosomes - Eukaryotic chromosomes contain DNA and protein, packed together to form chromatin - Chromatin consists of DNA tightly coiled around proteins called histones - DNA and histones together form nucleosomes Nucleosomes can fold huge lengths of DNA into the nucleus (the nucleus contains more than 1 meter of DNA!)

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30 CHROMOSOMES AND DNA REPLICATION DNA Replication: - Structure of DNA relates to its function - Each strand of DNA double helix has info needed to create the other half because of complimentary base pairing - Model of replication is semi-conservative because half of the parent molecule is maintained (conserved) in each daughter molecule

31 CHROMOSOMES AND DNA REPLICATION DNA Replication: - Eukaryotes - DNA replication occurs at hundreds of places and proceeds in both directions until each chromosome is replicated - Replication forks: sites where separation/replication of DNA occur - Prokaryotes - Replication begins at a single point and proceeds in two directions until entire chromosomes is replicated

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33 III. DNA REPLICATION Steps of DNA Replication: 1. Enzyme helicase unzips the strands of the double helix by breaking the hydrogen bonds that hold the bases together. 2. The separated strands of DNA serve as templates from which new copies can be made. 3. The now exposed bases are free to match up with their complementary bases to form another strand of DNA. 4. DNA polymerase adds new complementary DNA nucleotides to the template strand. - DNA strands have a 3 end and a 5 end - Primed numbers refer to the carbon atoms at the end - 3 end C is bonded to an OH and 5 end carbon is bonded to a phosphate group - DNA polymerase adds nucleotides to the 3 end ONLY 5. DNA ligase links new pieces together

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37 RNA RNA stands for Ribonucleic Acid 1. Monomers: RNA nucleotides. 2. Structural Differences between DNA and RNA: a) Sugar: ribose b) Bases: 1. Pyrimidines: uracil (U no T in RNA!),cytosine (C) 2. Purines: adenine(a), and guanine(g) c) Shape: single stranded.

38 DNA vs RNA Sugar Shape DNA Deoxyribose Double Helix RNA Ribose Single Strand Bases A, T, C and G A, U, C and G

39 Types of RNA: 1. Messenger RNA (mrna)-acts as a messenger between DNA and the ribosome. 2. Transfer RNA (trna)-carries amino acids to the ribosome that match up with the codons on mrna. 3. Ribosomal RNA (rrna a.k.a. ribosome)-site of protein synthesis - links amino acids together

40 TRANSCRIPTION 1. Definition: Transcription is the process by which a complementary mrna strand is made from DNA (DNA acts as a template). 2. Location: in cell nucleus. 3. Purpose: to transfer the instructions stored in DNA s bases into the bases of mrna. This is done so that mrna can leave the nucleus and take these instructions to the ribosome where it will be used to make proteins. (First step to making a protein) (TRANSCRIBE = to copy)

41 TRANSCRIPTION 4. Summary: a) The bases of DNA are grouped into 3 letter words. These words are called triplets. b) RNA polymerase (enzyme) attaches to DNA and separates the DNA strands. The RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mrna. RNA polymerase only binds to DNA in an area called the promoter region, which has a specific base sequence. The promoters are signals in DNA that tell the enzyme where to start making mrna. c) mrna bases are floating around in the nucleus and now can match up with their complementary DNA base: (A-U and C-G) with the help of RNA Polymerase. d) A strand of mrna is made which leaves the nucleus and heads to the ribosome carrying DNA s instructions.

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43 PROTEIN SYNTHESIS 1. Definiton: Protein Synthesis a.k.a. Translation is the decoding of a strand of mrna into a strand of amino acids (protein) 2. Location: on the ribosome in the cytoplasm of cells. 3. Purpose: to use the info (DNA s instructions) found in mrna s bases to link together amino acids to make proteins. (TRANSLATE = to decipher/decode or to interpret)

44 PROTEIN SYNTHESIS 4. Summary: a) The bases of mrna are grouped into 3 letter words too. These words are called codons. b) Each codon has a specific meaning, which is understood by the ribosome. Each codon represents an amino acid. (Codons code for amino acids) c) As each codon of the mrna moves through the ribosome, the ribosome decodes the codon s meaning and determines the amino acids that it represents. These amino acids are then brought to the ribosome by trna. d) trna matches up to the codons using an anticodon. Anticodons are 3 bases on trna anticodons match with codons e) These amino acids connect to one another through peptide bonds, forming a long chain called a polypeptide or a protein. Stop codons: codons on the mrna that signal the release of the polypeptide

45 Lysine TRANSLATION Messenger RNA is transcribed in the nucleus. Phenylalanine trna Lysine mrna Methionine mrna attaches to a ribosome and translation begins Anticodon Codon

46 TRANSLATION Growing polypeptide chain Amino Acid trna trna Ribosome mrna mrna Ribosome

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48 PROTEIN SYNTHESIS ANIMATIONS TRY IT YOURSELF!

49 TRANSCRIPTION AND TRANSLATION SUMMARY March 26, 2012

50 TYING IT ALL TOGETHER DNA codes for the AMINO ACIDS that make up a PROTEIN that determines a TRAIT!

51 MUTATIONS A mutation is any change (error) in the nucleotide sequence. It may involve a part of the chromosome, or only a single base pair. Mutations are caused by mutagens, physical or chemical agents that cause mutations. There are two types of mutations: Chromosomal Mutations Gene Mutations

52 Chromosomal mutations: changes in the number or structure of chromosomes There are four types of chromosomal mutations: - Deletions: involve the loss of all or part of a chromosome - Duplications: produce extra copies of parts of a chromosome - Inversions: reverse the direction of part of a chromosome - Translocations: when part of a chromosome breaks off and attaches to another

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54 Gene mutations affect the base sequence of mrna. There are two types of gene mutations: - Base Substitutions * Point Mutations * Silent Mutations - Base Insertions & Deletions * Frameshift Mutations

55 BASE SUBSTITUTIONS: Point Mutations-one base is replaced with another base that changes the mrna codon in a way that changes the amino acid. EX: DNA: AAT CGA Mutated DNA: AAT TGA mrna: UUA GCU mrna: UUA ACU Amino Acids: Leucine Alanine Amino Acids: Leucine Threonine DISEASES: CYSTIC FIBROSIS, HUNTINGTONS

56 BASE SUBSTITUTIONS (cont.): Silent Mutations-one base is replaced with another base that changes the mrna codon without changing the amino acid. EX: DNA: AAT CGA Mutated DNA: AAC CGA mrna: UUA GCU mrna: UUG GCU Amino Acids: Leucine Alanine Amino Acids: Leucine Alanine

57 BASE INSERTIONS AND DELETIONS: Frameshift Mutations-the inserting or deleting of one or more bases that shifts the groupings of bases for every codon following the mutation. EX: DNA: AAT CGA Mutated DNA: AAT TCG A mrna: UUA GCU mrna: UUA AGC U Amino Acids: Leucine Alanine Amino Acids: Leucine Serine DISEASES: SICKLE CELL ANEMIA

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