DNA and RNA PDF

© Amy Brown Science DNA, RNA, and Protein Synthesis © Amy Brown Science The Chemistry of Heredity By the 1940's, there was no doubt of the existence of chromosomes and that genes were found on the chromosomes. But there were so many questions that needed to be answered: What are genes and what do th...

© Amy Brown Science DNA, RNA, and Protein Synthesis © Amy Brown Science The Chemistry of Heredity By the 1940's, there was no doubt of the existence of chromosomes and that genes were found on the chromosomes. But there were so many questions that needed to be answered: What are genes and what do they do? What are genes made of? How do genes work? How do genes determine the characteristics of an organism? Genes must be capable of three critical things: 1. Genes must carry information from one generation to the next. 2. Genes must be able to put the information that they carry to work to produce the traits of the organism. 3. There must be a mechanism of easily copying the gene because the information must be replicated every time a cell divides. Chemical analysis shows that a chromosome is composed of … … half nucleic acid and half protein. It was originally thought that the protein portion of the chromosome carried the genetic information. Very little was known in the early days about the nucleic acids. This hypothesis was wrong. In 1953, James Watson and Francis Crick shook the scientific world with their model for the structure of DNA. It then became obvious that Mendel's heritable factors and the genes on chromosomes are composed of DNA. DNA molecules consist of small units called __________. nucleotides Several million nucleotides make up ________________. one strand of DNA Nucleotides consist of: nitrogen base a) a phosphate group b) a 5-carbon sugar called deoxyribose c) a nitrogen base phosphate group deoxyribose Phosphate + sugar + nitrogen base = 1 nucleotide Nitrogen Base (Double-ringed) Phosphate Deoxyribose Sugar Nitrogen Base (Single-ringed) Phosphate Deoxyribose Sugar Deoxyribose (in DNA) Ribose (in RNA) The sugar is a _____________ 5-carbon sugar called ___________. deoxyribose The four nitrogen bases found in DNA are: a) Adenine – A b) Guanine – G c) Thymine – T d) Cytosine – C NOTE: The nitrogen base uracil is only found in RNA. We will discuss uracil later. Guanine Adenine Cytosine Thymine Uracil Purines Pyrimidines Purines are double ring structures. Guanine and adenine are purines. Pyrimidines are single ring structures. Cytosine, thymine, and uracil are pyrimidines. Nucleotides are joined together to form ____. DNA backbone of a DNA chain is formed by alternating The _________ sugar and phosphate groups _________________________. The nitrogen bases stick out sideways from the chain. The nucleotides can be joined together phosphate in any order. In the image to the right, label the alternating sugar and phosphate molecules. Label the nitrogen bases and indicate if each is a purine or a phosphate pyrimidine. In the late 1940’s and early 1950’s, it was not understood how this molecule could carry the phosphate genetic information and put this genetic information to work in a cell. Nitrogen base (Purine) sugar Nitrogen base (Pyrimidine) sugar Nitrogen base (Purine) sugar Erwin Chargaff In 1947, an American scientist named Erwin Chargaff discovered that … … the amount of guanine and cytosine bases are equal in any sample of DNA. The same is true for the other two nitrogen bases. The amount of adenine and thymine are equal in any sample of DNA. The observation that A=T ______and that C = G became ______ known as Chargaff’s rules _______________. At the time this observation was made, it was not clear why this fact was so important. The X-Ray Evidence by Rosalind Franklin © Amy Brown Science In the early 1950’s, a British scientist named Rosalind Franklin began to study DNA. She used a process called _____________. X-ray diffraction She took a large, purified sample of DNA, aimed a powerful x-ray beam at the sample, then recorded the scattering pattern of x-rays on film. Franklin’s X-Ray Diffraction By itself, these x-rays did not reveal the structure of the DNA molecule, but it did provide clues about the structure. The x-rays showed that the strands in DNA are … … twisted around each other in a shape known as a helix. two strands in The x-rays suggested that there were ___________ the structure. It appeared that the _____________ nitrogen bases were at the center of the molecule. ______ At the same time that Franklin was doing her research, two scientists named Francis Crick and James Watson, were trying to understand the structure of DNA by building models of it. They were getting nowhere. The Players … James Watson Francis Crick Maurice Wilkins Rosalind Franklin Early in 1953, Watson was shown a copy of Franklin’s x-ray patterns, and he immediately realized how the DNA molecule was arranged. Within weeks, Watson and Crick built a model of DNA. It showed the structure of DNA. It explained how DNA could carry information and how it could be copied. Watson and Crick described the DNA double helix molecule as a ___________ or spiral consisting of two strands wound ___________ around each other. Timeline 1953 – Watson and Crick solve the structure of DNA 1958 – Rosalind Franklin dies of ovarian cancer at age 37 1962 – Watson, Crick, and Wilkins win the Nobel Prize The Watson and Crick Model of DNA A double helix looks like a ____________. twisted ladder The sides of the ladder are formed from alternating sugar and phosphate groups. The rungs of the ladder are formed by … … two nitrogen bases that pair together across the center of the helix. Alternating sugar and phosphate groups Two nitrogen bases paired across the center of the helix. The Watson and Crick Model of DNA hydrogen bonds. The two strands are joined by weak _________ Hydrogen bonds These hydrogen bonds form only between certain base pairs. Adenine is always thymine bonded to ________ and guanine is always bonded to ________. cytosine Hydrogen bonds The Watson and Crick Model of DNA This is called the “base pairing rules” and it explains Chargaff’s rules. There is a reason why A = T and G = C. Every adenine _______ in the DNA molecule is bonded to a thymine _______. Every ________ cytosine in the DNA molecule is bonded to a guanine _______. These are called complementary base pairs. hydrogen bond phosphate phosphate sugar phosphate sugar phosphate sugar sugar Covalent bond The two sides of the ladder are made up of alternating sugar _____ and phosphate _________ molecules. nitrogen bases nitrogen bases bases The rungs of the ladder are formed by the nitrogenous ________________. bases form each rung. Two ______ The bases are _________ covalently bonded to a _______________ sugar-phosphate unit. The paired bases meet across the helix and are joined together by ________ hydrogen bonds. Adenine always pairs _______ with _______. thymine Two ____ hydrogen bonds form between them. Two hydrogen bonds Three hydrogen bonds Guanine always ________ pairs with cytosine _______. _____ hydrogen Three bonds form between them. DNA as a Carrier of Information A necessary property of genetic material is that it be able to carry information. The DNA molecule is able to do this. The information is carried in the sequence of nitrogen bases and ________________________ any sequence of bases is possible. © Amy Brown Science DNA as a Carrier of Information Since the number of paired bases ranges from about 5,000 for the simplest virus to 6 billion in human chromosomes, the variations are infinite. If the DNA from a single human cell were stretched out, it would reach about 6 feet. It would carry information equivalent to 1,200 books as thick as your textbook! And yet all of this information can be copied in just a few hours with very few errors. How can all of this DNA fit inside a cell? The structure of the chromosome allows the DNA to be packed __________ very tightly inside the cell. DNA and proteins A chromosome is composed of_________________. The DNA is wrapped tightly around proteins called ________. histones DNA histones nucleosome Together, the DNA and histone molecules form a beadlike structure nucleosome called a ___________. chromosome How can all of this DNA fit inside a cell? DNA Nucleosomes pack with one another to form a thick fiber, which is shortened by a nucleosome system of loops and coils. histones chromosome Nucleosomes seem to be able to fold enormous lengths of DNA into the tiny space available in the cell nucleus. Replication of DNA – An Overview The structure of DNA allows it to be easily copied or replicated. Each strand of the double helix has all the information needed to construct the other half by the mechanism of base pairing. Because each strand can be used to make the other strand, the strands are said to be complementary. Replication of DNA – An Overview The strands will be _________, separated and the rules of base pairing will allow ___________ new strands to be constructed. Replication: The process by which a cell copies or duplicates its DNA. Replication of DNA – An Overview During DNA replication, the molecules separate into two strands. Each strand serves as a template for producing a new strand. Two new complementary strands are produced according to the base paring rules. Steps in Replication two complementary strands of DNA. 1. The parent molecule has ________________________ Each base is paired to its specific partner by _______________. hydrogen bonding Adenine always pairs with thymine _______. guanine Cytosine always pairs with _______. Steps in Replication 2. The first step is the _________ separation of the two DNA strands. The ______________ hydrogen bonds are broken between the bases. Each parental strand now serves as a ________. template Steps in Replication 3. New __________ nucleotides are inserted along both sides (both templates). nitrogen base pairs with its As the molecule “unzips”, each ____________ new strand just like the old one. complement to form a __________ One at a time, nucleotides line up along the template strand according to the ________________. base-pairing rules Steps in Replication 4. The nucleotides are connected to form the sugar-phosphate backbones of the new strands. Covalent bonds are formed between the sugars and the phosphates to join the nucleotides together. Hydrogen bonds are formed to link the two complementary bases together. Where there was one double-stranded DNA molecule at the beginning of the process, there are now two. Each is an exact replica of the parent molecule. The Mechanisms of Replication – A Detailed View The replication of an enormous amount of genetic information is achieved with very few errors. There is only one error per 10 billion nucleotides. The replication is a speedy and accurate process. 2. In large eukaryotic chromosomes, DNA replication occurs at hundreds of points along the molecule. Replication then proceeds in both directions until the entire DNA molecule has been replicated. This allows very long DNA molecules to be replicated very quickly. 3. The site where the DNA molecule separates and replication occurs is called a replication fork. 4. More than a dozen enzymes and proteins participate in DNA replication. Replication begins at special sites called "origins of replication." Origin of Replication Origin of Replication Origin of Replication DNA Origins of Replication are short stretches of DNA that have a specific sequence of nucleotides. Origin of Replication Origin of Replication Origin of Replication DNA Replication Fork Replication Bubble Proteins that initiate DNA replication recognize this sequence and attach to the DNA at these sites, separating the two strands and opening up a “replication bubble." Origin of Replication Origin of Replication Origin of Replication DNA Replication Fork Replication Bubble Replicating DNA DNA DNA Replication then proceeds in both directions, until the entire molecule is copied. The DNA in a eukaryotic cell may have hundreds of replication origins, speeding up the copying of the very long DNA molecules. Replication fork: A "Y" shaped region at the end of each replication bubble where the new strands of DNA are elongating. Replicating the DNA Replication: The process by which a cell copies or duplicates its DNA. During DNA replication, the … …two strands separate, and two replication forks are formed. New _____ bases are added according to the base pairing rules. For example: If there is _______ adenine on the template strand, then a nucleotide with ________ thymine is added to the newly forming strand. Original Template DNA Strand New nucleotides are added in this way until the entire molecule has been ______. copied Replication Fork Free Nucleotides Original Template DNA Strand Each side of the double helix of DNA serves as a ________ template for a __________. new strand Question: If the template strand has the bases ACTGCA, what new complementary strand would be produced? Answer: TGACGT The end result of replication is the production of … … two DNA molecules identical to each other. Each DNA molecule has one _______ original strand and one new strand. ____ How Replication Occurs There are many enzymes involved in the replication of DNA. HELICASES a) This group of enzymes Replication Fork breaks the hydrogen bonds between complementary base pairs. b) This “unzips” the DNA Helicase molecule, forming two replication forks. c) When the hydrogen bonds are broken, the two strands of the DNA molecule unwind allowing each strand to serve as a template for the attachment of the new nucleotides. d) Helicases are enzymes that untwist the double helix at the replication forks, separating the two parental strands and making them available as template strands. How Replication Occurs DNA POLYMERASES DNA Polymerase Replication Fork a) DNA polymerase is a major enzyme involved in DNA replication. b) These enzymes add the new nucleotides to DNA Polymerase the existing chain. c) The rate of elongation is about 50 nucleotides per second in human cells. d) DNA polymerase also proofreads each new DNA strand to ensure that an exact copy has been made. e) Eleven different DNA polymerases have been discovered so far. Enzymes Proofread DNA As DNA polymerase adds nucleotides to the growing DNA strand, there is an error rate of about 1 in 100,000 base pairs. DNA polymerases proofread as nucleotides are added. If a mistake is found, the DNA polymerase removes the nucleotide and resumes synthesis. A good analogy is hitting the delete key when you make a typing error. Errors in the completed DNA strand amount to only 1 in 10 billion nucleotides since many of the errors are corrected before replication is completed. © Amy Brown Science Accidental changes can occur in existing DNA after replication. damaged The DNA can become _________ from exposure to chemicals, radioactivity, X-rays, ultraviolet light, and molecules in cigarette smoke. Each cell continuously monitors and repairs its genetic material. About 130 DNA repair enzymes have been identified so far. Repairing the Damage Step A: A damaged section of DNA is detected. Step B: The damaged segment of DNA is cut out by enzymes called nucleases. Step C: The resulting gap is filled in with new nucleotides by DNA polymerases. Step D: Other enzymes ( ligases ) seal the free ends of the new DNA to the old DNA, making the strand complete. You now know that the DNA molecule carries the instructions for the structure and functioning of the cell and passes these instructions on to new cells. How are the instructions carried out? How do genes work? The Genetic Code The DNA molecule, with its four code for nitrogenous bases, is the _____ proteins that are made in a cell. all ________ DNA Genes are made of _____. A gene is the coded DNA instructions that controls the proteins production of specific ________, such as enzymes, structural proteins, oxygen-carrying proteins, etc. The DNA inherited by an organism dictates the synthesis of certain proteins. Proteins are the link between genotype and phenotype. The proteins that are made will determine what traits show up in the offspring. Gene expression: The process by which DNA directs the synthesis of proteins. The expression of genes includes two stages: Transcription and translation. The Code Is A Triplet 1. Proteins are made of building blocks called amino acids. 2. There are ___ 20 different amino acids and ____ four different nucleotides (since there are four different nitrogenous bases). 3. It was discovered that three nucleotides in sequence must specify each amino acid __________. This would provide 64 possible for ___ combinations of amino acids. triplet of nucleotides is called a ______. codon 4. Each ______ 5. Each codon calls for a specific __________. amino acid When many amino acids are linked together a ______ protein is made. ___________ 6. A few codons do not call for any amino acids. start codon. One codon acts as a ”_____" sequence of nucleotides A start codon is a specific ______________________ that indicates where the protein-building instructions begin ________________. stop codons and act as Three other codons are “____” end of a protein chain signals for the ___________________. 7. A _____ gene on a chromosome is many, codons long. many _______ Each gene is the code for a protein particular _______. 8. Genes provide the ___________ instructions for making specific proteins but a gene does not build a protein directly. ________, bridge between DNA and protein synthesis is RNA The ______ _____. RNA – Ribonucleic Acid Differences Between DNA and RNA 1. RNA is a single strand. DNA is a double strand. RNA – Ribonucleic Acid Differences Between DNA and RNA 2. The sugar in RNA is ribose. The sugar in DNA is deoxyribose. Double strand Single strand Deoxyribose Ribose RNA – Ribonucleic Acid Differences Between DNA and RNA 3. In RNA, uracil pairs with adenine. In DNA, thymine pairs with adenine. U Function of RNA Proteins are made by the ribosomes _________ in the cytoplasm. DNA determines which proteins need to be made. Function of RNA gene on the DNA A _____ copied molecule is ______. RNA This copy is called ____. The copy of the instructions is then sent out to the ribosomes in the cytoplasm. _________ message RNA carries the ________ from the DNA (in the nucleus to the ribosomes _______) cytoplasm (in the _________). RNA tells the ribosomes … … which proteins to make and how to make them. Three Types of RNA In the drawing to the right, label the three different types of RNA. Ribosomal RNA (rRNA) Messenger RNA (mRNA) Transfer RNA (tRNA) Messenger RNA (mRNA) 1. Messenger RNA travels from the nucleus to the cytoplasm (ribosomes) with the instructions for making proteins. messenger between the 2. Messenger RNA (mRNA) is the “__________” DNA in the nucleus and the ribosomes in the cytoplasm. Messenger RNA (mRNA) 3. The instructions are carried in the form of codons. The first codon is called the “start” codon. This is the point at which mRNA will attach to the ribosome. This tells the ribosome where the protein-building instructions begin. 4. The rest of the molecule is a _____________________ sequence of nucleotides that amino acids for the particular dictates the sequence of ___________ protein that is being made. _______ stop ” codon. 5. The last codon is called the “____ This tells the ribosome to _________________ stop the production of the protein. Transfer RNA (tRNA) anticodon transfer RNA has an 1. Each ___________ _________ anticodon at one end and an binding site at the amino acid __________ other end. transfer RNA amino acid The bases composing the complementary anticodon are _____________ to mRNA codons. 2. Transfer RNA reads the message carried by mRNA and gathers the amino acids for making the protein. Transfer RNA (tRNA) 3. Transfer RNA transfers amino acids from the cytoplasmic pool of amino acids to a ribosome. 4. A cell keeps its cytoplasm stocked with all 20 amino acids. 5. One end of the tRNA attaches to one amino acid and carries it to the ribosome. Ribosomal RNA - rRNA transfer RNA ribosomal RNA messenger RNA ribosomal RNA Ribosomal RNA is found in the ribosome. These are used to bind the mRNA and the tRNA to the ribosome. This allows all components required for the synthesis of the proteins to be held together. Transcription of RNA – An Overview 1. Transcription is the process of… … forming a strand of RNA from a strand of DNA. 2. This process occurs in the nucleus. 3. The cell must make RNA to cytoplasm to tell send to the _________ the ribosomes _________ how and which proteins _______ to make. 4. The RNA molecule is a faithful copy of a gene’s protein building instructions. This type of RNA is called messenger RNA (mRNA). Transcription of RNA – An Overview 5. An enzyme called RNA polymerase catalyzes this reaction. 6. The purpose of transcription is to copy one gene from the DNA molecule. 7. Where does one gene end and the next gene begin? a) Promoter: A DNA sequence where RNA polymerase attaches and initiates transcription. b) Terminator: The DNA sequence that signals the end of transcription. Steps of Transcription RNA polymerase binds to a site on _______________ the DNA molecule called the promoter _________. RNA polymerase Inactive DNA strand Template strand of DNA RNA polymerase … … separates the DNA strands. One strand of DNA is used as a template ________. New nucleotides are inserted according to the base pairing rules. When transcribing RNA, adenine pairs with uracil _____. guanine Cytosine pairs with ________. Steps of Transcription This continues until the __________ terminator is reached. RNA polymerase Inactive DNA strand Template strand of DNA mRNA transcript As the RNA polymerase moves along the DNA hydrogen molecule, ________ bonds between the two strands of DNA are reformed ________. A singled stranded RNA molecule has been transcribed. Remember: The purpose of transcription is not to copy the entire length of the DNA molecule, but to copy only a single gene. The mRNA transcript will be sent to the ribosome as the instructions for protein synthesis. RNA Processing and Editing The RNA is not yet ready to be sent out to the cytoplasm. modified before it is It must be ________ ready to serve its purpose. The mRNA is a copy of a small section of DNA. The mRNA contains sections introns and other called ______ exons sections called _____. RNA Processing and Editing Introns are sequences of nitrogen bases that are ___________ not involved in the making of the ______. protein These need to be cut out of the RNA before the RNA goes to the ribosomes. Exons are the sequences of are involved nitrogen bases that ___________ in the making of the protein. RNA Processing and Editing Promoter: Transcription Start Site exon intron Terminator: Transcription End Site Transcription Pre-mRNA exon RNA Editing intron Introns are cut out and removed. When mRNA is formed, both the introns and exons are copied from the DNA. introns are _______ However, the _______ cut out of the RNA while the RNA is still inside the nucleus. RNA Processing and Editing Promoter: Transcription Start Site exon Terminator: Transcription End Site intron Transcription Pre-mRNA exon RNA Editing intron Splicing Introns are cut out and removed. Remaining exons are spliced together to form mRNA. Edited mRNA is sent to ribosomes after the additional of a cap and tail. spliced back together to form The remaining exons _____ are ___________________ the final RNA. RNA Processing and Editing TAIL CAP cap and tail are added to form the final RNA molecule. Finally, a ___________ front end ” of the RNA from The cap and tail help to identify the “ ________ back end ”. the “ ________ The cap and tail help the ribosome to identify the _____ start of the instructions and the ____ end of the instructions. If introns are not needed and will be cut out of the RNA, why are they there in the first place? When introns are present in genes, it allows a single gene to code for more than one type of protein, depending on which segments are treated as introns and which are treated as exons. When particular segments are cut out, one type of protein might result. If different segments are cut out, a different type of protein would result. The Genetic Code Proteins are made by joining together … … long chains of amino acids. The _____ order in which the amino acids are joined type of protein that is made. determines the _____________ The “language” of mRNA instructions is called the genetic code. The genetic code is read three nitrogen bases at a time. Each group of three nitrogen bases is called a codon _____. A codon is a group of three nitrogen bases that specifies ______________. one amino acid Consider the following mRNA sequence, for example: AGA CUG GCA mRNA A G A C U G G C A The sequence would be read three bases at a time: AGA - CUG - GCA These three codons represent three different ___________. amino acids From your chart of amino acids, determine the three amino acids coded for by these codons: Arginine Leucine Alanine CCA UCA GGA Since there are four different bases read in three groups of _____, there are ___ 64 possible codons. ACG ACU GAU CCC GCU AUG UUU CUU AGC UAC GCA UCG UGA CAA AAC CUC GUC A U G S TA RT There is one codon, ____, AUG which specifies the amino methionine acid, __________. This codon serves as the “start” codon for protein synthesis. This codon is found at the beginning of every set of mRNA instructions. This codon “tells” the ribosome where the instructions will start. There are three “_____” stop codons. These do not code for any amino acid. U G A STOP U A A STOP U A G STOP Stop codons act like the period at the end of the sentence. Stop codons signify ___________________. the end of the protein Protein Synthesis – Translation The synthesis of proteins is called translation __________. The cell must translate the base sequence of an mRNA molecule into the amino acid sequence of a protein. Protein Synthesis – Translation Linking of amino acids tRNA Large ribosomal subunit mRNA Small ribosomal subunit The site of translation _________, or protein synthesis, occurs in the ribosome ________. The ribosome facilitates the orderly linking of amino acids into proteins. During translation, the cell uses information from mRNA to produce proteins. Steps in Protein Synthesis 1. In the nucleus, DNA transcribes RNA. 2. The RNA is sent to the cytoplasm in the form of mRNA. 3. The mRNA attaches to a ribosome. codon of the 4. As each ______ mRNA molecule moves ______________ through the ribosome, the proper __________ amino acid is brought into the ribosome tRNA by _____. The amino acids are lined up in the right order on the ribosome. Steps in Protein Synthesis 5. The ribosome hitches the amino acids together with peptide bonds and _____________ polypeptides are made. ___________ Remember, a polypeptide is a long chain of amino acids but is not a functioning protein. Polypeptides are sent to the endoplasmic reticulum and the Golgi apparatus where they are modified and 6. See your handout for a list of all shaped into functioning codons and their amino acids. proteins. Transfer RNA transfer amino acids from the The function of tRNA is to __________________ ribosome cytoplasm’s amino acid pool to a _________. 20 amino acids. A cell keeps its cytoplasm stocked with all ___ tRNA to The ribosome adds each amino acid brought to it by _____ polypeptide chain. the growing end of a ___________ Transfer RNA molecules are not all the same. Each type of tRNA molecule links a mRNA codon particular ____________ with a particular amino acid __________. Transfer RNA anticodon As a tRNA arrives at a ribosome, it carries a specific __________ amino acid at one end. tRNA amino acid At the other end is a _______________ nucleotide triplet anticodon called an _________. mRNA codons For example: If an mRNA codon is ____, GAC this would translate as the amino acid aspartic acid (Asp) _________________. The tRNA that delivers the amino acid aspartic acid has as its anticodon ____. CUG aspartic acid It carries ___________ at its other end. tRNA anticodon Each tRNA is used repeatedly to locate a amino acid particular __________ amino acid and deposit it at the ribosome ________. It then leaves the ribosome to go and find another amino acid. The codons must be read correctly and in the correct order. Consider the statement: The red dog ate the cat. What happens if the reading of the code starts at the wrong place? Consider the same sentence. Read the letters in groups of three, but omit the “T” at the beginning of the sentence her edd oga tet hec at. © Amy Brown Science The codons must be read correctly and in the correct order. Consider the statement: The red dog ate the cat. her edd oga tet hec at. gibberish The result will be _________. A polypeptide will be made by putting the wrong amino acids in order. It is unlikely that this protein function will be able to ________. Putting It All together! If the sequence on the DNA molecule calls for a protein with the following DNA codons: (1) What would be the sequence of the mRNA codons? (2) What would be the sequence of the tRNA anticodons? (3) What would be the amino acid sequence of the protein being made? DNA sequence TAC TTA CAA ACC ATA ATT mRNA codons AUG AAU GUU UGG UAU UAA tRNA anticodons UAC UUA CAA ACC AUA AUU Valine Tryptophan Tyrosine STOP Amino acids Methionine Asparagine (Start) A More Detailed Look at Translation Large ribosomal subunit Small ribosomal subunit A ribosome is made up of two ___________. subunits They are called the ____________ large subunit and the ____________. small subunit The subunits are constructed of ________ proteins and RNA molecules named ribosomal ___________________. RNA (rRNA) A More Detailed Look at Translation Large ribosomal subunit mRNA Small ribosomal subunit These subunits are made in the _________ nucleolus and are exported to the _________. cytoplasm Large and small subunits join to form a __________________ functional ribosome mRNA molecule. only when they attach to an ______ A More Detailed Look at Translation amino acid tRNA tRNA anticodon Large ribosomal subunit mRNA Small ribosomal subunit mRNA codon anticodon whose bases are Each transfer-RNA has an _________ complementary to a ______ codon on the mRNA strand. ______________ amino acid Each tRNA arrives at the ribosome carrying a specific __________. Ribosomal Binding Sites growing polypeptide P E site site A site Each ribosome has a binding site for ______ mRNA and three binding sites for tRNA _____. The three tRNA binding sites are called the … … E site, the P site, and the A site. mRNA The P site holds … …the tRNA carrying the growing polypeptide chain. Ribosomal Binding Sites growing polypeptide tRNA exits the ribosome from the E site P E site site A site The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. Next amino acid to be added to polypeptide. mRNA Discharged tRNA’s leave the ribosome from the E site. STEPS OF TRANSLATION Translation: The process of translating the base sequence of an mRNA molecule into the amino acid sequence of a protein. The ____________ mRNA arrives from the nucleus and attaches to the ribosome. As each ______ codon of mRNA moves through the _________, ribosome the proper __________ amino acid is brought into the ribosome by _____. tRNA Translation begins with the start codon, AUG. AUG is the codon calling for the amino acid methionine. This signals the start of translation. Each tRNA has an _________ anticodon that is complementary to a codon _____ on the mRNA strand. For the mRNA start codon AUG, the anticodon on tRNA is ____. UAC A tRNA with the anticodon UAC arrives at the ribosome carrying the amino methionine acid __________. As each mRNA codon is “read”, the proper amino acid is delivered and attached to the growing polypeptide chain. © Amy Brown Science Note the 4 images in the diagram of protein synthesis. Let’s examine what is happening in each of the four images used in the cycle. Growing polypeptide tRNA enters the A site carrying an amino acid Image 1: An incoming _____ tRNA binds to the mRNA A site codon in the _____. A tRNA holding the growing polypeptide chain sits at the P site. Note the 4 images in the diagram of protein synthesis. Let’s examine what is happening in each of the four images used in the cycle. Growing polypeptide tRNA enters the A site carrying amino acid Peptide bond Image 2: peptide bond is formed A ____________ between the amino acid in the P _____ site with the newly arrived amino acid at the ______. A site Note the 4 images in the diagram of protein synthesis. Let’s examine what is happening in each of the four images used in the cycle. Growing polypeptide Image 3: To form this peptide bond, the existing polypeptide chain at the P site is shifted to the A site to join the newly arriving amino acid. tRNA enters the A site carrying amino acid Peptide bond Polypeptide shifted to A site Note the 4 images in the diagram of protein synthesis. Let’s examine what is happening in each of the four images used in the cycle. Growing polypeptide Polypeptide shifts to P site. “Empty” tRNA moves to E site, and is released from ribosome Image 4: The ribosome now moves the tRNA in the A site, with its attached polypeptide chain, to the P site. As it moves, the mRNA moves along with it. The tRNA that was in the P site moves to the E site and is released from the ribosome. tRNA enters the A site carrying amino acid Peptide bond Polypeptide shifted to A site The polypeptide continues to grow until the ribosome reaches the STOP codon on the mRNA. When the STOP codon is reached, the newly formed polypeptide and the mRNA molecule are released from the ribosome. The Relationship Between Genes and Proteins Genes are nothing more than… … instructions for building proteins. What do proteins have to do with the color of a flower, a human blood type, or dimples? The answer is – EVERYTHING! The traits of any organism are the result of the proteins being built within the cells. On occasion cells make __________________________. mistakes in copying their DNA incorrect nitrogen base may be inserted, or a base An ____________________ may be skipped altogether. These mistakes are called mutations _________. Mutations are changes in the genetic material of a cell. gene mutations or Mutations may be either _____ chromosome mutations. ____________ Gene mutations produce a change single gene within a __________. Chromosome mutations produce changes in the _____ whole chromosome. Point Mutations Point mutations are changes in just … … one base pair of a gene. These are called point ______________ mutations because they occur at a single __________ point in the DNA sequence. There are Two Types of Point Mutations Base Pair Substitutions: One nitrogen base is changed to another. Note the point mutation at base 2 in the above sequences. What happens when the “G” at the second base is substituted with a “T”? There are Two Types of Point Mutations Base Pair Insertions or Deletions: A nitrogen base is inserted or removed from the DNA sequence. Note the point mutation at base 2 in the above sequences. What happens when there is a deletion at the second base? How will the ribosome “read” the mRNA? Base Pair Substitutions 1. A base pair substitution is the replacement of one nitrogen base with another. 2. It would affect just the one amino acid coded for by that codon. 3. If the substitution is in the 3rd position, it may not have any effect on the organism since there is some redundancy of codons. Base Pair Substitutions: An Example The codons for alanine are GCU, GCC, GCA, and GCG. A point mutation at the third position would have no effect whatsoever. The codon would still call for the amino acid alanine. These are called silent mutations. Base Pair Substitutions 4. If the substitution were in the ____________________, first or second position it would have a greater ______ effect. amino acid would The wrong ________________ be called for and inserted chain into the polypeptide _______________ that is being manufactured. Only that one amino acid would be affected. may or may not have any effect on 5. A switched amino acid ______________ the proper functioning of that protein. area such as If the alteration of a single protein is in a crucial __________, the active site on an enzyme, the protein will not function properly. Practice Problem Questions: What amino acid would be called for by the codon AAG? Answer: Lysine What would happen if an “A” was substituted at the third position in this codon? Answer: The codon AAA would still call for the amino acid lysine. There would be no effect on the protein being made. What would happen if a “C” was substituted at the third position in this codon? Answer: The codon AAC would call for the amino acid asparagine. The protein being made would be altered. What would happen if there was a substitution at the 1st or 2nd position in this codon? Answer: The wrong amino acid will be called for. The protein being made would be altered. Insertions and Deletions 1. If a nitrogen base is inserted or removed from the DNA sequence, the code is still read in three-base codons, but now those three-base groupings are shifted for every codon that follows. 2. These mutations have a disastrous effect on the resulting protein. Insertions and Deletions 3. For example, consider this codon sequence: AUG AAU GUU UGG UAU UAA If the “G” is deleted in the first codon, the codons would be read as follows: AUA AUG UUU GGU AUU AA The codons are still read in groups of three nitrogen bases. All of the nucleotides that are downstream of the deletion or addition will be improperly grouped into codons. The addition or deletion of a base would alter the reading of the entire rest of the mRNA. frameshift mutations. 4. These are called __________ 5. Frameshift mutations can alter a protein so much that … … it is unable to perform its normal functions. The Importance of Mutations 1. Most gene mutations are neutral _______. They have … … little or no effect. 2. Some mutations cause such dramatic changes that normal cell functions are disrupted and may result in a genetic disorder. 3. Mutations that occurs in the _________ body cells of an organism affect only that organism ________. For example, mutations in some body cells may lead cancer to ______. not passed to future offspring These mutations are __________________________. Mutations that occur during gamete production can be passed to future offspring and may lead to new variations of phenotypes within a population. If these mutations create a favorable change in the offspring, the offspring may be better suited for the environment. Those organisms that are better suited are more likely to survive, reproduce, and pass these favorable traits on to their offspring. This is the mechanism of Natural Selection. Created by Amy Brown Copyright © Amy Brown Science All rights reserved by author. This document for s your Teisrm Te ofclassroom Use use only. This document may be electronically distributed OneDrive™ or educational apps wherenot the How to Copy/Paste Our Credit Graphic graphics are moveable pieces that can be from site, a PDF except for permitted oreasily posted todigital a resources public lifted. 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