dna, rna and protein synthesis
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DNA, RNA and Protein Synthesis. TAKS Review. Structure of DNA. DNA is deoxyribonucleic acid DNA is a large molecule that has subunits called nucleotides . The nucleotides come together to make the DNA molecule in the shape of a double helix (looks like a twisted ladder). Nucleotides. - PowerPoint PPT PresentationTRANSCRIPT
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DNA, RNA and Protein Synthesis
TAKS Review
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Structure of DNA
• DNA is deoxyribonucleic acid
• DNA is a large molecule that has subunits called nucleotides.
• The nucleotides come together to make the DNA molecule in the shape of a double helix (looks like a twisted ladder).
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Nucleotides
• Nucleotides are the subunits that make up DNA and they have 3 major parts:
1. A sugar molecule (deoxyribose sugar)
2. A phosphate group 3. A nitrogen base
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Nitrogen bases
There are 4 kinds of nitrogen bases:
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
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DNA Structure
• DNA is a double helix (twisted ladder)
• The handrails of the ladder are made of phosphate and sugar
• The rungs of the ladder are made of nitrogen bases.
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Bonding
• Sugar and phosphate bond using covalent bonds (strong) and nitrogen bases bond using hydrogen bonds (weak)
• Nitrogen bases are specific: Adenine (A) always attaches to Thymine (T); and Cytosine (C) always attaches to Guanine (G)
• (Think apples in trees, cars in garages)
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DNA Replication
A review:
A cell will make an exact copy of itself during a process called mitosis
Before the cell can copy itself it must copy all of it’s DNA so that both daughter cells have the same number of chromosomes.
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DNA replication takes place in 3 steps
• 1. DNA unwinds at the hydrogen bonds
• 2. nucleotides are added to the exposed nitrogen bases. It follows base pairing rules. (A –T and C-G)
• 3. The DNA winds back up producing 2 new strands.
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What’s the complementary strand?
• If one side is CAG, what is the complementary strand?
• Answer: GTC
• If one side is AAC, what is the complementary strand?
• Answer: TTG
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RNA vs DNA
Characteristic RNA DNA
Strands 1 2
Sugar molecule Ribose Deoxyribose
Bases A, U, C, G A, T, C, G
Found Nucleus and cytoplasm
Nucleus only
Building block Nucleotide Nucleotide
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Kinds of RNA
• There is only one kind of DNA, but there are 3 kinds of RNA.
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
– Ribosomal RNA (rRNA)
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http://onlinetc.its.brooklyn.cuny.edu/Core81/chap5.html#jump2
Gene Expression
DNA (double-stranded)
RNA (single-stranded)
Protein (amino acid chain)
Transcription Translation
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Central Dogma of Molecular Biology
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http://www.wappingersschools.org/RCK/staff/teacherhp/johnson/visualvocab/mRNA.gif
Transcription= taking DNA and making an RNA copy of it. Uses complementary
nucleotides. C=G, G=C, T=A, A=U
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The Genetic Code
• Remember that messenger RNA – mRNA- is a copy of the DNA. It carries instructions for making a protein.
• The instructions (nucleotides) have to be translated into proteins (amino acids).
• A sequence of three nucleotides is called a codon, and it corresponds to an amino acid.
• We use a codon chart for translation
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•
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Genetic Mutations
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Mutation• A mutation is any change in a genetic code (DNA).• It may not change the resulting amino acid chain
and is called a silent mutation• EXAMPLE: Notice how the resulting a.a. sequence is
the same in spite of the change:– Original DNA: CAA CCC AAA– Resulting mRNA: GUU GGG UUU– Resulting amino acid: Val – Gly - Phe– Mutated DNA: CAA CCC AAG– Resulting mRNA GUU GGG UUC– Resulting amino acid: Val – Gly – Phe
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Point Mutation or Substitution Mutation• A point mutation is a change in one nucleotide. It
can be silent or it can cause a change in one amino acid
• Can be devestating if the resulting amino acid has a STOP codon inserted as a result– Original DNA: ATG CCC AAA– Resulting mRNA: UAC GGG UUU– Resulting amino acid: Tyr – Gly - Phe– Mutated DNA: ATG ACC AAA– Resulting mRNA UAC UGG UUU– Resulting amino acid: Tyr – Trp – Phe– Mutated DNA: ATT CCC AAA– Resulting mRNA: UAA GGG UUU– Resulting amino acid: Stop
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Insertion and Deletion Mutations• Insertion – addition of one or more nucleotides• Deletion – deletion of one or more nucleotides• Insertion and deletion mutations are almost
always devastating because it will cause a frame-shift to occur.
• Imagine if a sentence of 3-letter words lost a letter?
• Original sentence: The cat and dog are fat.• A mutation occurs that deletes the c in cat.• Mutated sentence: Thc ata ndd oga ref at.• The same things happen to DNA when it mutates
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Frame Shift Mutation
• Original DNA: CAT AGC TAG GAT• Resulting mRNA: GUA UCG AUC CUA • Resulting amino acid: Val–Ser-Ile-Leu • Mutated DNA: CAA GCT AGG AT• Resulting mRNA: GUU CGA UCC UA
• Resulting amino acid: Val-Arg-Ser-?
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Mendel’s Theory and Studying Heredity
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The Flower
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Mendelian Theory of Heredity
• 2 sets of chromosomes = 2 copies of each gene
• Alleles—alternative forms of a gene– Purple vs. white flowers
• Dominant allele—trait that is expressed or seen.
• Recessive allele—trait that is not seen. To be seen, must be present in 2 copies.
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Terms and Notations
• Dominant alleles = capital letters
• Recessive alleles = lower case letters
• Dominant allele is always written first
• Homozygous individual—alleles are the same (EX: PP or pp)
• Heterozygous individual—alleles are different (EX: Pp)
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Terms and Notations Continued
• Genotype—set of alleles, or genes.
• Phenotype—physical appearance of a trait.
Genotype PhenotypePP purple flowers, homozygous
dominant
Pp purple flowers, heterozygous
pp white flowers, homozygous recessive
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Punnett Squares
• Diagram that predicts the outcome of a genetic cross
• Top represents one parent, side the other
• Letters in the box indicate the possible genotypes of the offspring.
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Example Punnett Square
Y y
Y
y
Yy—heterozygote
Yy—heterozygote
YY Yy
Yy yy
¼=YY homozygous dominant
2/4=Yy heterozygous
¼=yy homozygous recessive
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Inheritance of Traits
• Pedigree—family history that shows how a trait is inherited over several generations.
• Helps identify carriers of genetic disorders
• Carriers—individuals who are heterozygous for a genetic disorder but do not show symptoms—can pass the mutant allele to their offspring
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Example Pedigree
Male
Female
Male with disorder
Female with disorder