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Transcript of DNA / RNA
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DNA / RNA
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DNA
• Deoxyribonucleic acid (DNA) is a nucleic acid that contains the blueprint for making the proteins the cell needs.
• DNA contains genes.
• Genes are specific messages instructing the cell on how to construct a protein.
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DNA
• DNA is the chemical used to pass genetic information on to the next generation of organisms.
• DNA controls the synthesis of proteins, which helps determine the characteristics of the organism and regulate the cell’s metabolism.
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DNA
• DNA contains the genetic instructions used in the development of all known living organisms and some viruses.
• DNA molecules are used for long term storage of information.
• DNA carries the instructions necessary to create RNA and proteins; therefore, it is often compared to a blueprint.
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DNA Structure
• DNA is a nucleic acid.
• Nucleic acids are large polymers of nucleotides.
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DNA Structure
• DNA consists of two long polymers of simple units known as nucleotides.
• These two strands run in opposite directions to each other and are therefore known as anti-parallel.
• The strands have backbones made of sugars with phosphate groups attached.
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DNA Structure
• Attached to each sugar is one of four types of molecules called bases.
• Information is encoded in the sequence of these four bases along the backbone.
• The information is read using the genetic code.
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DNA Structure
• The genetic code specifies the sequence of amino acids within proteins.
• The code is read by copying stretches of DNA into RNA (A process known as transcription).
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DNA Structure
• A nucleotide consists of a sugar molecule, a phosphate group, and a nitrogenous base.
• There are four different nitrogenous bases in DNA:
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DNA Structure
• Adenine (A), guanine (G), cytosine (C), and thymine (T).
• The DNA nucleotides can combine into a long linear DNA molecule that can pair with another linear DNA molecule.
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DNA Structure
• The two paired strands of DNA form a double helix with sugars and phosphates on the outside and the nitrogenous bases on the inside.
• The nucleotides form hydrogen bonds with one another, which helps to stabilize the helical structure.
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DNA Structure
• Adenine pairs with Thymine (A-T).
• Guanine pairs with Cytosine (G-C).
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Nitrogenous Bases
• The nucleotide bases are nitrogenous bases that are involved in pairing in DNA and RNA. This is known as base pairing.
• In genetics they are simply called bases.
• Adenine, Guanine, Cytosine, and Thymine are DNA bases.
• Adenine, Guanine, Cytosine, and Uracil are RNA bases.
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Adenine
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Guanine
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Thymine
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Cytosine
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Uracil
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Chromosomes
• Within cells, DNA is organized into structures called chromosomes.
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Chromosomes
• The chromosomes are duplicated before the cell divides, a process known as DNA replication.
• Within the chromosomes, chromatin proteins such as histones compact and organize DNA. The chromatins help determine which parts of the DNA are transcribed.
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Eukaryotes Vs. Prokaryotes
• Eukaryotic organisms (animals, plants, fungi, and protists) store their DNA inside the cell nucleus.
• Prokaryotic organisms (bacteria and archae) have no nucleus; therefore, the DNA is found in the cytoplasm.
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DNA Replication
• When a cell grows and divides, two new cells result.
• DNA replication is the process by which a cell makes another copy of its DNA.
• Base pairing rules and many enzymes make replication possible.
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DNA Replication
• DNA replication is the process of copying a double-stranded DNA molecule to form two double-stranded molecules.
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DNA Replication
• Each DNA strand holds the same genetic information; therefore, both strands can serve as a template for the reproduction of the complementary strand.
• The template strand is conserved in its entirety and the new strand is assembled from nucleotides. This is known as semiconservative replication.
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DNA Replication
• The resulting double-stranded DNA molecules are identical.
• DNA replication must happen before cell division can occur.
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DNA Replication
• Helicases are enzymes that bind to the DNA and separate the two strands of DNA.
• DNA polymerase incorporates DNA nucleotides into the new DNA strand. The nucleotides enter according to the base pairing rules.
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DNA Replication
• In prokaryotic cells, this replication process starts at only one place along the DNA molecule (origin of replication).
• In eukaryotic cells, the replication starts at the same time along several different places of the DNA molecule.
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DNA Replication
• Two new identical, double-stranded DNA molecules are formed.
• The new strands of DNA form on each side of the old DNA strands.
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DNA Replication
• The exposed nitrogenous bases of the original DNA serve as the pattern on which the new DNA is formed.
• Two double helices are formed with identical nucleotide sequences.
• A portion of the DNA polymerase molecule edits the newly created DNA molecule and makes corrections if needed.
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DNA Replication
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Repair of Genetic Information
• If an error or damage occurs to the DNA helix on one strand, the pairing arrangement of nitrogenous bases on the other undamaged strand can be read.
• This information is used to repair the damaged strand.
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DNA Code
• DNA stores information.
• The order of the nitrogenous bases is the genetic information that codes for proteins.
• The nucleotides are read in sets of three.
• Each sequence of three nucleotides is a codeword for a single amino acid.
• The information to code one protein can be thousands of nucleotides long.
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RNA Structure And Function
• Ribonucleic Acid (RNA) is important in protein production.
• RNA’s nucleotides contain a ribose sugar whereas DNA’s nucleotides contain a deoxyribose sugar.• Ribose has an –OH group and
deoxyribose has an –H group on the second carbon atom.
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RNA Structure And Function
• RNA contains the nitrogenous bases Uracil (U), guanine (G), cytosine (C), and adenine (A).
• DNA is found in the cell’s nucleus, while RNA is made in the nucleus and then moves out into the cytoplasm of the cell.
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RNA Structure And Function
• DNA directs protein synthesis by using RNA.
• RNA is made by enzymes that read the protein coding information in DNA.
• RNA nucleotides pair with DNA nucleotides.• RNA contains Uracil instead of Thymine
so adenine in DNA pairs with Uracil in RNA.
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Nucleic Acid Base Pairing Rules
DNA pairs with DNA
DNA pairs with RNA
RNA pairs with RNA
A pairs with T A pairs with U A pairs with U
T pairs with A T pairs with A U pairs with A
G pairs with C G pairs with C G pairs with C
C pairs with G C pairs with G C pairs with G
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Transcription
• Transcription is the process of using DNA as a template to synthesize RNA.
• The RNA polymerase enzyme reads the sequence of DNA nucleotides and follows the base pairing rules between DNA and RNA to build the new RNA molecule.
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Transcription
• The two strands of the double stranded DNA molecule are separated to expose the nitrogenous bases.
• The DNA’s nitrogenous bases are read and paired with the RNA nucleotides.
• Only one strand of the DNA molecule is read (the coding strand). The other strand is referred to as the non-coding strand.
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Transcription
• Promoter sequences are specific sequences of DNA nucleotides that RNA polymerase uses to find a protein-coding region of DNA and to find out which strand of DNA is the coding strand.
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Transcription
• Termination sequences are DNA nucleotide sequences that indicate when RNA polymerase should finish making an RNA molecule.
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3 Types of RNA
• Messenger RNA (mRNA) – carries the blueprint for making the necessary protein.
• Transfer RNA (tRNA) – reads mRNA and brings in the necessary amino acids.
• Ribosomal RNA (rRNA) – reads the mRNA and brings in the necessary amino acids.
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Translation
• Translation is the process of using information in RNA to direct protein synthesis.
• mRNA is read in sets of three nucleotides called codons.
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Translation
• A codon is a set of three nucleotides that codes for a specific amino acid.
• The ribosome is made up of proteins and ribosomal RNA (rRNA).
• The ribsome holds the mRNA in place and reads it’s codons.
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3 Phases of Translation
• Initiation
• Elongation
• Termination
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Initiation
• The small ribosomal subunit binds to the mRNA and moves along until it reaches an AUG codon to signal the beginning of translation.
• Transfer RNA (tRNA) carries amino acids to the mRNA complex.
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Initiation
• The anticodon portion of the tRNA interacts with the mRNA to match the correct amino acid to the codon in the mRNA nucleotide sequence.
• The tRNA that binds to the AUG codon that signals the beginning of translation carries the amino acid methionine; therefore, every protein begins with this amino acid.
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Elongation
• The ribosome functions as an assembly line.
• New amino acids are carried by tRNA to the corresponding mRNA segment.
• The anticodon on tRNA matches with the codon on mRNA.
• The amino acid is then attached to the end of the chain and the protein becomes elongated.
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Termination
• The ribosome will continue to add new amino acids until a stop signal is reached on the mRNA molecule.
• The stop codon can be either UAA, UAG, or UGA.
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Termination
• When these codons are encountered, a release factor enters the ribosome. The ribosomal subunits release mRNA.
• The mRNA can then either be reused or broken down to stop protein production.
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Translation
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Nearly Universal Genetic Code
• The code for making protein from DNA is the same for nearly all cells.
• Bacteria, protists, plants, fungi, and animals all use DNA to store their genetic information.
• They all transcribe information in DNA to RNA.
• They all translate the RNA to synthesize protein using a ribosome.
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Nearly Universal Genetic Code
• Almost all use the same three nucleotide codons to code for the same amino acid.
• In eukaryotic cells, transcription always occurs in the nucleu, and translation always occurs in the cytoplasm.
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Nearly Universal Genetic Code
• These similarities make it possible to use bacteria to synthesize human proteins (i.e. insulin).
• Some viruses use RNA to store their genetic information (retroviruses). HIV is an example of this. Retroviruses use RNA to make DNA, which is then used to make proteins.
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Gene Expression
• Gene expression occurs when a cell transcribes and translates a gene.
• Cells control which genes are used to make proteins.
• The different cell types in the human body are due to which proteins the cell is producing.
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Controlling Protein Quantity
• An enzymes activity can be regulated by controlling how much of that enzyme is made.
• The cell controls how much mRNA is available for translation, which in turn determines the quantity of the protein produced.
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Controlling Protein Quantity
• Enhancer and silencer sequences affect the ability of RNA polymerase to transcribe a specific protein.
• Enhancer sequences increase protein synthesis by increasing transcription.
• Silencer sequences decrease protein production by decreasing transcription.
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RNA Degradation
• Cells regulate gene expression by limiting the length of time that mRNA is available for translation.
• Enzymes in the cell break down mRNA.
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Mutations
• A mutation is any change in the DNA sequence of an organism.
• Errors during DNA replication can cause mutation.
• External factors can cause mutation:
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Mutations
• Radiation, carcinogens, drugs, viruses.
• Not all mutations cause a change in the organism.
• If the mutation occurs away from the protein-coding sequence of the DNA, it is unlikely to be harmful to the organism.
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Silent Mutation
• A silent mutation is a change that does not change the amino acids used to build a protein.
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Nonsense Mutation
• A nonsense mutation causes a ribosome to stop protein synthesis by introducing a stop codon too early.
• This prevents the formation of functional proteins.
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Missense Mutation
• A missense mutation causes the wrong amino acid to be used in making a protein.
• This will change the shape of the protein and affect its active sites.
• This can cause an abnormally functioning protein.
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Insertions And Deletions
• Some mutations involve larger spans of DNA than a change in a single nucleotide.
• An insertion mutation adds one or more nucleotides to the normals DNA sequence.
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Insertions And Deletions
• This can add amino acids to the protein and change its function.
• A deletion mutation removes one or more nucleotides.• This can delete amino acids from the
protein and change its function.