Date post: | 03-Jan-2016 |
Category: |
Documents |
Upload: | valentine-burris |
View: | 88 times |
Download: | 8 times |
DNA and RNA
What does DNA look like?
What are the elements that makeup DNA?
DNA Structure= String of nucleotides (sugar, phosphate, base)
*Adenine*Thymine*Guanine*Cytosine
•purines - adenine, guanine
•pyrimidines - cytosine, thymine
Purines Pyrimidines
Adenine Guanine Cytosine Thymine
Phosphate group Deoxyribose
Figure 12–5 DNA Nucleotides
Francis Crick and James Watson (1953)
Twisted Double Helix
Hydrogen Bonds are the “glue” that keeps
the two strands together
Each strand of the helix is a chain of nucleotides
What holds the strands together?
Always Together….Great CoupleD
E
N
I
N
E
H
Y
M
I
N
E
U
A
N
I
N
E
Y
T
O
S
I
N
E
A & T G & C
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?
Remember Chromatin??
DNA tightly coiled around proteins forming Chromatin which pack together to form thick fibers.
What exactly is chromatin?
ONE nucleus of ONE human cell = more than 1 meter of DNA!!!
Chromosome
E. coli bacterium
Bases on the chromosome
Prokaryotic Chromosome Structure
Section 12-2
Chromosome Structure of Eukaryotes
Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
How can DNA use its double-stranded structure to its advantage for replication???
“Something Old…Something New”
DNA Replication 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 (something “OLD”)
3) Free nitrogen bases form bonds and make complementary strands (Something “NEW”)
Template
4) DNA Polymerase bonds the nucleotides and proofreads the molecule
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 deoxyribose2. RNA – usually single-stranded3. RNA has uracil to replace thymine (so U
binds with A)
“Always United & Great Couple”
RNA is in charge of assembling Amino Acids into Proteins
From DNA(Gene) to Protein
rRNA - ribosomal RNA - location of protein synthesis uses tRNA to make proteins
The players:
DNA - sequences of nitrogen bases forms the genetic code
mRNA - messenger RNA - makes a copy of the DNA in the nucleus and brings it to the rRNA
tRNA - transfer RNA - reads the mRNA and brings specific amino acids to the rRNA
Step 1: Transcription = recording the message Occurs in nucleus New mRNA strand forms from one of DNA
strands (creating the message) Let’s Practice…
Transcription Practice
Transcribe the DNA molecule below:
ATTATCGCGTAATGCTAATAGC
TAATAGCGCATTACGATTATCG
Template
AUUAUCGCGUAAUGCUAAUAGC
mRNA
transcript
RNADNA
RNApolymerase
Figure 12–14 Transcription
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
Step 2: Editing of mRNA
Introns are removed – non coding regions of the DNA molecule
Exons remain – sequences that will be expressed
Step 3: Translation = Protein Synthesis Occurs at ribosome tRNA reads mRNA which has message from
genetic code (DNA) Genetic code is read 3 letters at a time, so
each word is 3 bases long
Every 3 letters is a CODON
Each codon codes for a specific amino acid.
What does an Amino Acid do again? Helps make proteins!
•We need codons for Protein Synthesis (Translation)
•They are like directions to make proteins
•Every set of directions tells you where to START and where to STOP
•We too have these, we call them the “start and stop codons”
Codons to remember…
START is always: AUG
STOP is always: UAA UAG UGA
Translation Explained
tRNA UAC mRNA AUGCGCAUAACGCAU
Start Codon
methionine
Alternate sequence:
There are 20 different amino acids to be coded for.
There are 64 possible codons.
Start codon
Stop codon
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
Figure 12–18 TranslationSection 12-3
Figure 12–18 Translation (continued)
Section 12-3
Mutations - changes in the DNA sequence Gene mutation- changes in a single gene
• Point Mutations - substitution of one nucleotide for another
• Frame Shift Mutations - shifting of the genetic code due to insertion or deletion of nucleotide
Chromosomal mutation changes in the entire chromosome (containing many genes)
Deletion
Duplication
Inversion
Translocation
Figure 12–20 Chromosomal Mutations
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
When a mutation occurs…
If the amino acid sequence is stopped early (a STOP codon is reached) = Nonsense
If the amino acid sequence continues but the wrong amino acids are coded for = Missense
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