chapter 12 : dna and rna what does dna look like? what are the elements that makeup dna?
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Chapter 12 : DNA and RNA
What does DNA look like?
What are the elements that makeup DNA?
What is DNA?
What is DNA?Discovered by Watson & Crick in 1953A long molecule made up of units, called nucleotidesGenes are made of DNADescribed as a twisted ladder, or a double helix
Made up of nucleotides Each nucleotide has 3 parts
* a sugar called deoxyribose* a phosphate group* a nitrogen base
There are 4 nitrogen bases:purines - adenine, guaninepyrimidines - cytosine, thymine
* Every purine pairs with a pyrimidine in order to make a DNA chain
DNA Structure
Purines Pyrimidines
Adenine Guanine Cytosine Thymine
Phosphate group Deoxyribose
Figure 12–5 DNA Nucleotides
•Twisted double helix made of two strands
•Each strand of the helix is a chain of nucleotides
•Held together by hydrogen bonds
Always Together….Great Couple
A & T G & C
•Every nucleotide is paired with a another from the opposite strand.
•Each pair is specific (Chargaff’s Rule).
•Adenine and Thymine pair together
•Guanine and Cytosine pair together
Base Pairing of Nucleotides
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Figure 12–7 Structure of DNA
How is DNA organized in a chromosome?
• A nucleus of ONE human cell has more than 1 meter of DNA!!!
•Chromatin: a substance consisting of DNA tightly coiled around proteins called histones.
•The DNA and histones together are called nucleosomes (bead-like structure)
Figure 12-10 Chromosome Structure of Eukaryotes
Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
Chromosome
E. coli bacterium
Bases on the chromosome
Prokaryotic Chromosome Structure
Section 12-2
How can DNA use its double-stranded structure to its advantage for replication???
DNA Replication (Refer to Figure 12-11)When does this occur in the cell cycle?
1) Enzymes un-twist and unzip the molecule (break H bonds between base pairs).
2) Each strand serves as a template
3) Free nitrogen bases form bonds and make complementary strands which follow the base pairing rules.
Template
Figure 12–11 DNA Replication
Growth
Growth
Replication fork
DNA polymerase
New strand
Original strand DNA
polymerase
Nitrogenous bases
Replication fork
Original strand
New strand
DNA vs. RNA
RNA – also a long chain of nucleotides (5-carbon sugar, phosphate group, nitrogenous base)
Differences:
1. RNA sugar = ribose, instead of deoxyribose
2. RNA – usually single-stranded
3. RNA does not have thymine. 1. Uracil instead.
2. Adenine and Uracil pair
RNA is in charge of assembling Amino Acids into Proteins
Transcription: a sequence of DNA is copied into an RNA strand Transcribe the DNA molecule below:
TAATAGCGCATTACGATTATCG
AUUAUCGCGUAAUGCUAAUAGC
•RNA will only start and stop at specific regions of the DNA called promoters.
•We need codons for Protein Synthesis.
•They are directions to make proteins
•Every set of directions tells you where to START and where to STOP (start and stop codons)
•AUG: START UAA, UAG, UGA: STOP
•Proteins are made by joining amino acids into long chains (POLYPEPTIDES)
•Each polypeptide consists of a combo of any or all 20 amino acids.
•Amino acids contain 3 nucleotides. The 3 nucleotides are read as a code called a codon.
•A CODON specifies a single AA that is added to the polypeptide.
Translation Explained
tRNA UAC mRNA AUGCGCAUAACGCAU
Start Codon
Anticodon
methionine
Figure 12–17 The Genetic Code
Translation Practice
Make a polypeptide (chain of amino acids) chain from the mRNA molecule
AUGAUCGCGUAUUGCUACUAG - mRNA
methionine-isoleucine-alanine-tyrosine-cysteine-tyrosine STOP
Mutations - changes in the DNA sequence Gene mutation- changes in a single gene Chromosomal mutation changes in the
entire chromosome (containing many genes)1) Point Mutations - substitution of one nucleotide for
another
2) Frame Shift Mutations - shifting of the genetic code due to insertion or deletion of nucleotide
Mutation AnalogyTHE FAT CAT ATE THE RAT
substitution THE FAT CAT ATE THE CAT *The letter “C” was substituted for the “R”
insertion THE FAT CAT ATE THE RAT THC EFA TCA TAT ETH ERA T
*Because the “C” was added, all other letters shifted down, thereby changing the amino acids that are made.
C
Deletion THE F T CAT ATE THE RAT
THE FTC ATA TET HER AT*Again, the amino acids will change b/c the “F” was removed
A
Mutation Practice
What will the new amino acid be if the 5th nucleotide is substituted with an adenine?
AUGA CGCGUAUUGCUACUAG - mRNAU
What will the new amino acid sequence be if a guanine is inserted between the 9th and 10th nucleotide ?
ASPARAGINE
G
GUA = VALINE
Putting it all together
What is the amino acid sequence that forms from the following DNA molecule? (DNA synthesis)
TACTACACCGTATAACAGGGCCTAGCAACT
Template
ATGATGTGGCATATTGTCCCGGATCGTTGA
(Transcription)DNA - TACTACACCGTATAACAGGGCCTAGCAACT
mRNA - AUGAUGUGGCAUAUUGUCCCGGAUCGUUGA
(Translation)
amino acid sequence
methionine-methionine-tryptophan-histidine-isoleucine-valine-proline-aspartic acid-arginine-stop
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