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Unit 1: Central Code and Genetic Material Paz Etcheverry NS 315 Topics to cover Cell structure DNA structure DNA replication RNA structure The Central Dogma of Biochemistry Transcription: DNA to mRNA Translation: mRNA to protein Codons and anticodons Cell structure Cytosol or cytoplasm The nucleus: contains 23 pairs of chromosomes. DNA is arranged in these chromosomes. Where replication and transcription occurs. The ribosome: where protein is synthesized (i.e. translation occurs) DNA structure The nucleus: contains 23 pairs of chromosomes. DNA is arranged in these chromosomes 23 pairs of chromosomes: http://ghr.nlm.nih.gov/handbook/basics/howmanychromosomes How many chromosomes does each human cell have? Each human cell contains 46 chromosomes: – 22 pairs of somatic (non sex) chromosomes – 2 sex chromosomes: Female sex chromosomes: 2 X Male sex chromosomes: 1 X and 1 Y A chromosome pair Centromere DNA Inside each of the 23 pairs of chromosome, there is DNA. DNA is tightly packed inside each of the chromosomes. Each chromosome is composed of two chromatids joined by a centromere. DNA (deoxyribonucleic acid) Double helix Double= 2 polynucleotide chains Helix= helical structure (like a spring) Each chain contains nucleotides (joined to each other) and a sugar/phosphate backbone http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif Nucleotides in DNA The nucleotides are – – – – Adenine (A) Thymine (T) Cytosine (C) Guanine (G) A binds to T C binds to G A and G= purine bases T and C= pyrimidine bases http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure%5b1%5d.gif Sugar backbone Sugar backbone Notice how the two sugar chains run opposite each other: The 5’ end (which has a phosphate group), faces the 3’ end (which has a hydroxyl (OH) group) and vice versa. Who discovered the structure of DNA? James Watson, a young American scientist and Francis Crick, a young English researcher. In 1953, Watson and Crick published a paper in which they proposed and described the structure of DNA. Rosalind Franklin (an English researcher) was within a couple days of coming to the same conclusion when their paper was published. Watson and Crick received the Nobel prize in 1962. Rosalind Franklin died in 1958 of ovarian cancer, probably due in large part to her work with x-rays. Since the Nobel prize is not awarded posthumously, people have often wondered if the Nobel committee would have included Franklin if she had still been alive. http://biology.clc.uc.edu/courses/bio104/dna.htm DNA replication What is DNA replication? DNA replication is a fundamental process occurring in all living organisms to copy their DNA. The point of DNA replication is to ensure that each of our cells contain the same copy of DNA when the cells divide. http://www.le.ac.uk/ge/genie/vgec/images/mitosis_meiosis.png Replication-Steps 1) The DNA unzips (helix opens up) 2) DNA polymerase (enzyme) starts bringing new nucleotides and building two DNA molecules 3) At the end of the replication procedure, there will be 2 DNA molecules each with a parent chain and a daughter (new) chain DNA replication is very important Replication ensures that when our cells divide, so does our genetic information (DNA) http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/ch10_DNA-rep.jpg RNA structure RNA (ribonucleic acid) The structure is like the DNA except that it is single stranded (1 strand as opposed to 2 strands/chains) It contains 1 polynucleotide chain and the nucleotides are: – – – – Adenine (A) Uracil (U) –no Thymine in RNA Guanine Cytosine http://en.wikivisual.com/images/0/04/NA-comparedto-DNA_thymineAndUracilCorrected.png Types of RNA Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA) The Central Dogma of Biochemistry The Central Dogma of Biochemistry • • Life depends upon the ability to change genetic information into functional proteins. This is referred to as the central dogma of biochemistry and consists of two processes: • transcription • translation The Central Dogma of Biochemistry transcription DNA in the nucleus translation RNA in the cytosol Protein The Central Dogma of Biochemistry transcription DNA in the nucleus translation RNA in the cytosol Protein Transcription: The synthesis of mRNA Transcription Occurs in the nucleus (in eukaryotes) It is the process whereby a copy of DNA (called mRNA) is made, via action of RNA polymerase RNA polymerase reads DNA from 5’ to 3’ end The residues are paired DNA RNA A U (remember no T in RNA) T A G C C G RNA polymerase 5’ 3’ http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html RNA polymerase 3’ 5’ DNA http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html Transcription Occurs in the nucleus (in eukaryotes) It is the process whereby a copy of DNA (called mRNA) is made, via action of RNA polymerase RNA polymerase reads DNA from 5’ to 3’ end The residues are paired DNA RNA A U (remember no T in RNA) T A G C C G Transcription (contd) When RNA polymerase binds to DNA to transcribe the DNA into mRNA, it binds to a part of DNA called the promoter region. Promoter region (where RNA polymerase binds) 5’ Response element DNA 3’ Area that will be ‘read’ by RNA polymerase to create mRNA Promoter region DNA 5’ 3’ RNA polymerase mRNA DNA 5’ 3’ RNA polymerase Notice how RNA polymerase reads DNA from the 5’ end to the 3’ end strand. mRNA DNA 5’ 3’ RNA polymerase RNA polymerase mRNA 5’ 3’ RNA polymerase dislodges from the DNA when it reads an unusual sequence of DNA Translation: The synthesis of proteins from mRNA The Central Dogma of Biochemistry transcription DNA in the nucleus translation RNA in the cytosol Protein Translation Once mRNA was synthesized (via transcription), it leaves the nucleus of the cell and goes to the cytoplasm (aka cytosol) In the cytoplasm, there is an organelle called the endoplasmic reticulum (ER) which contains ribosomes Ribosomes facilitate protein synthesis protein amino acid tRNA mRNA rRNA http://www.biologycorner.com/resources/translation_lettered.jpg Translation (contd) During translation, mRNA binds to rRNA (ribosomal RNA). tRNA (transfer RNA) holds one amino acid in the form of amino acyl-tRNA complex The mRNA guides the order (sequence) of amino acids forming the protein rRNA serves as an anvil, aligning both mRNA and tRNA so that a peptide or protein is formed Step 1 of Translation mRNA AUG CCA ACG AUA UCC AGG GAG UAG mRNA, produced in the nucleus through the process of transcription, is now in the cytoplasm of the cell. Step 2 of Translation mRNA AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) rRNA binds to the mRNA strand. It serves to hold the mRNA in place. Step 3 of Translation met tRNA mRNA UAC AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) A tRNA (transfer RNA) that matches the sequence in mRNA (AUG) arrives, carrying an amino acid. AUG codes (codon) for methionine (met) Step 4 of Translation pro mRNA met GGU AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) The first tRNA leaves the scene. Another tRNA that matches the sequence CCA in mRNA arrives, carrying the amino acid proline (pro). Step 5 of Translation thr met pro mRNA UGC AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) The second tRNA leaves the scene. Met and pro form a bond (peptide bond) Another tRNA that matches the sequence ACG arrives, carrying the amino acid threonine (thr). Step 6 of Translation tyr met pro thr mRNA UAU AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) The last tRNA leaves the scene. Pro and thr form a bond (peptide bond) Another tRNA that matches the sequence AUA arrives, carrying the amino acid tyrosine (tyr). Final Step of Translation Stop codon met pro thr tyr mRNA ser arg glu AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) UAG is a stop codon, which tells the tRNA that no more amino acids should be incorporated. When a stop codon is reached, rRNA dissociates from mRNA and a protein is formed. The protein that is synthesized via translation Can become enzymes (compounds that speed up a reaction): – Enzymes involved in digestion – Enzymes involved in metabolism Can become muscle proteins Can become transport proteins that allow entry of certain molecules inside the cell Can become hormones (insulin, cortisol, adrenaline, etc) Etc… Amino acids and protein Amino acids (there are 20 of them in nature) are the building units of protein. Amino acids include: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Proline, Serine, Threonine, Tryptophan, Tyrosine, Valine Codons and anticodons Translation tyr met pro thr UAU AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) mRNA More about translation… Three nucleotides (in a specific order) code for a specific amino acid The nucleotide sequence in the mRNA is called codon The corresponding nucleotide sequence in the tRNA is called the anticodon Translation tyr anticodon met pro thr UAU AUG CCA ACG AUA UCC AGG GAG UAG rRNA (ribosomal RNA) codon mRNA protein amino acid tRNA anticodon codon mRNA rRNA http://www.biologycorner.com/resources/translation_lettered.jpg Amino Acid DNA Base Triplets mRNA Codons tRNA Anticodons alanine CGA, CGG, CGT, CGC GCU, GCC, GCA, GCG CGA, CGG, CGU, CGC arginine GCA, GCG, GCT, GCC TCT, TCC CGU, CGC, CGA, CGG AGA, AGG GCA, GCG, GCU, GCC UCU, UCC asparagine TTA, TTG AAU, AAC UUA, UUG aspartate CTA, CTG GAU, GAC CUA, CUG cysteine ACA, ACG UGA, UGC ACA, ACG glutamate CTT, CTC GAA, GAG CUU, CUC glutamine GTT, GTC CAA, CAG GUU, GUC isoleucine TAA, TAG, TAT AUU, AUC, AUA UAA, UAG, UAU leucine AAT, AAC, GAA, GAG GAT, GAC UUA, UUG, CUU, CUC CUA, CUG AAU, AAC, GAA, GAG GAU, GAC lysine TTT, TTC AAA, AAG UUU, UUC methionine TAC AUG UAC phenylalanine AAA, AAG UUU, UUC AAA, AAG proline GGA, GGG, GGT, GGC CCU, CCC, CCA, CCG GGA, GGG, GGU, GGC serine AGA, AGG, AGT, AGC TCA, TCG UCU, UCC, UCA, UCG AGU, AGC AGA, AGG, AGU, AGC UCA, UCG stop ATG, ATT, ACT UAA, UAG, UGA AUG, AUU, ACU http://waynesword.palomar.edu/codons.htm The start and end codon The start codon is the one that makes the tRNA insert its first amino acid The start codon is usually AUG and codes for methionine So almost all proteins begin with methionine as its first amino acid The stop codon is the one that makes the tRNA stop inserting amino acids UAA, UAG, UGA are all stop codons Summary… Cytosol or cytoplasm The nucleus: contains 23 pairs of chromosomes. DNA is arranged in these chromosomes. Where DNA replication and transcription occurs. DNA replication: DNA copies itself, every time the cell divides. Transcription: A copy of DNA is made. This copy is called mRNA. The ribosome: where protein is synthesized (ie translation occurs). In translation, mRNA is converted into protein. replication transcription DNA in the nucleus translation RNA in the cytosol Protein Replication of DNA is important, since it ensures that every cell will have a Copy of DNA each time the cell undergoes division. Central Dogma of Biochemistry: Life depends upon the ability to change genetic information into functional proteins, via the processes known as transcription and translation.