Chapter 12: DNA , RNA, and Proteins
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Transcript of Chapter 12: DNA , RNA, and Proteins
A. DNA— deoxyribonucleic acid; determines an organism’s traits by controlling when proteins in the body are made
1. Proteins and enzymes —control most aspects of cellular function in an organism
B. Structure of DNA1. Made of long chains of nucleotides
a. 3 parts of a nucleotide: - phosphate group - simple sugar
(deoxyribose) - nitrogen base
b. 4 types of nitrogen bases: - adenine (A)
- guanine (G) - cytosine (C)
- thymine (T)
Adenine (A)Guanine (G) Thymine (T)Cytosine (C)
Adenine (A)Guanine (G) Thymine (T)Cytosine (C)
d. Nucleotides join together in long chains to form nucleic acids.
c. Complementary base pairs: - A pairs with T - G pairs with C
2. All organisms are made up of the same nucleotides, just in
different ordera. Example: All words are made
up of the same letters, just in different order
A. Discovered by James Watson and Francis Crick in 1953.
1. Double Helix — double stranded, twisted ladder shape of DNA
2. If DNA is a ladder:a. Sugar and phosphate groups form the backbone or the sides of the ladderb. Nitrogen bases form the rungs of the ladder.
James Watson and Francis Crick
3. Individual nucleotides are joined by covalent bonds.
4. Nitrogen bases in the middle of the
helix are joined by hydrogen bonds.
B. How does DNA fit in the cell?1. Think about it! The DNA strand can be
incredibly LONG! Human DNA molecules contain up to 4,639,221,000 base pairs. That means there is about 1-2 meters of DNA in each cell. How can it be kept in such a small area?
2. The solution:a. Chromatin is made of DNA
packed around histone proteins.b. During interphase, these are
dispersed and uncoiled. When cells enter prophase, they pack tightly to form chromosomes.
A. DNA Replication - Whenever a cell divides, the DNA must be copied before it splits
1. DNA helicase, an enzyme, unzips the double helix (breaks the hydrogen bonds) to
form two single strands still joined at the replication forks.
Replication Fork Replication Fork
DNA helicaseDNA helicase
2. DNA polymerase, an enzyme, adds new nucleotides to each single strand according to their complementary base pairs
a. DNA polymerase also “proofreads” for errors
Replication Fork Replication Fork
DNA helicaseDNA helicase
DNA polymerase
3. DNA Ligase, an enzyme, reseals the gaps remaining in the sugar/phosphate backbone
to finish.
Replication Fork Replication Fork
DNA helicaseDNA helicase
DNA polymeraseDNA ligase
4. END RESULT: 2 new and identical molecules of DNA are formed
a. 1 strand made of “old” DNAb. 1 strand made of “new” DNA
Original DNA
Original DNA Strand
Original DNA Strand
Free NucleotidesNew DNA molecule
New DNA Strand
New DNA molecule
Replication
ReplicationDNA
5. Example Complementary Base Pairing a. (Find each complementary base pair for the strand of DNA)A—C—T—A—G—A—C—C—T—A—G—T | | | | | | | | | | | |
T G A T C T G G A T C A
6. Example of DNA Replication a. (Unzip the following molecule of DNA, and write the two new strands of DNA that would result from the replication)b. Original DNA Molecule
C—G—T—C—A—T—C—G—C—A—A—T—G | | | | | | | | | | | | |G—C—A—G—T—A—G—C—G—T—T—A—C
Molecule #1
C—G—T—C—A—T—C—G—C—A—A—T—G | | | | | | | | | | | | |G—C—A—G—T—A—G—C—G—T—T—A—C
Molecule #2
| | | | | | | | | | | | |G—C—A—G—T—A—G—C—G—T—T—A—C
C—G—T—C—A—T—C—G—C—A—A—T—G
A. DNA- Double stranded nucleic acid that is stored in the nucleus of the cell.
1. Gene- piece of DNA that controls a specific trait
B. RNA - a single stranded nucleic acid found all over the cell (nucleus, cytoplasm, and ribosome)
1. Made of long chains of nucleotides:
a. 3 parts of a nucleotide—
-phosphate group
- simple sugar (ribose)
- nitrogen base
b. 5 types of Nitrogen Bases- adenine (A)- guanine (G)- cytosine (C) - thymine (T)- Uracil (U)
c. Complementary base pairs - A pairs with U - T pairs with A - G pairs with C
d. Nucleotides join together in long chains to form nucleic acids.
2. Three Types of RNA
a. Messenger RNA (mRNA)- carries the information from the DNA in the
nucleus to the rest of the cell
Codon
b. Transfer RNA (tRNA)- helps build proteins by carrying amino acids to ribosomes, following instructions coded for in the mRNA.
Each tRNA carries only ONE type of amino acid
The code of the tRNA is complementary to the mRNA.
Amino acid
Chain of RNA nucleotides
Transfer RNA molecule
Anticodon
c. Ribosomal RNA (rRNA)- the site of protein synthesis; makes up the ribosome
Molecule DNA RNA
Sugar Deoxyribose Ribose
Structure Double strand Single strand
Nucleotides A, T, G, C
Adenine - thymine
A, U, T, G, C
Adenine - uracil
Thymine - Adenine)
Location in cell
Stays in the nucleus
Leaves nucleus to ribosomes
C. DNA/RNA Comparison
DNAtranscription
RNA Proteintranslation
D. Protein Synthesis - Using genetic information in DNA to make proteins
E. Steps of Protein Synthesis1. Transcription - Process of
making mRNA from DNA a. Why? DNA can’t leave
nucleus but RNA can
b. Steps of Transcription
1. RNA polymerase, an enzyme, unzips the double helix of DNA inside the nucleus and uses it as a template to create a complementary mRNA strand
2. RNA editing occurs Introns - sections of the DNA that don’t code
for proteins are cut from the mRNA Exons - sections of the DNA that code for
proteins are left on the mRNA
3. DNA rezips and mRNA leaves nucleus and goes to the cytoplasm to find a ribosome for protein synthesis
c. Example: Transcribe the DNA into mRNA.
A C C A T G A C C T G A C T T A C U G G U A C U G G A C U G A A U G
2. Translation: Making chains of amino acids (proteins) by reading/translating mRNA codons (a group of 3 nucleotides) in the ribosome
a. The amino acid sequence determines the structure and function of proteins
codon
b. Steps of Translation
1. mRNA travels to ribosome with a message from the DNA and attaches to the rRNA.
1.
2.
2. 3.
2. As each mRNA codon moves over the ribosome, it is matched with its
complementary tRNA anticodon, which is carrying amino acids.
1.
2.
2. 3.
3. Inside the ribosome, peptidase, an enzyme, helps form peptide bonds joining amino acids to make proteins and tRNA is released to go find another amino acid
1.
2.
2.
3.
c. Example: Translate the mRNA into proteins (USE CODON CHART!)
mRNA = A U G C A U G G A A G C U G A amino acid chain =
d. There are 20 amino acids created from a combination of the 4 nitrogen bases
- Each mRNA codon specifies a different tRNA anticodon to
bring amino acids to join to the protein
- Every different combination of amino acids forms new proteins
AlanineMethionine
Peptide bond
Special Codons - some codons signal start or stop
AUG (methoinine) = start building protein
UAA, UAG, and UGA = stop building protein
Stop codon
Process Transcription Translation
Location In Nucleus At the ribosome
Purpose Turn DNA into RNA
Turn RNA into proteins
Molecules involved
DNA, mRNA mRNA, tRNA, rRNA
3. Transcription/Translation Comparison
A. Mutation - Mistake or change in DNA sequence
1. The change in the DNA is HUGE since the codon is changed
a. If the codons are affected, the amino acids and proteins for the cell are also affected.
B. Types of Mutations1. Point Mutation - change in a
SINGLE base pair in DNAa. Substitution Mutation - one
nitrogen base is replaced with another
- Example: ACTAGGCAC to ACTAGTCAC
- Results in a change of one codon
Point mutation
mRNA
Protein
NormalmRNA
Protein
b. Frameshift Mutation - ONE base is added or deleted from DNA, and it shifts the reading of codons
- Example: Addition Mutation: ACTAGGCAC to
ACTAGGGCAC
Deletion Mutation: ACTAGGCAC to ACTAGCAC
- Results in EVERY codon after the mutation to change.
- Original Protein: Meth-Lys-Phenyl-Gly-Ala- Leu
- Mutated protein: Meth-Lys-Leu-Ala-Hist- Cys
Deletion of U
Without mutation
Frameshift mutation
mRNA
Protein
Addition(Frameshift)
Deletion(Frameshift)
Substitution (Point)
Normal
2. Which type of mutation is more serious? a. Frameshift - it affects EVERY amino acid/protein after the mutation
Deletion of U
Frameshift mutation
mRNA
Protein
3. Chromosomal mutations - Structural changes in chromosomes
a. Are especially common in plants.
4. Four Types of Chromosomal Mutations
a. Deletion -part of a chromosome left out (usually deadly)
A B C D E F G H
Deletion
A B C E F G H
b. Duplication/Insertion: chromosome part breaks off and reattaches to its sister chromatid
A B C D E F G H A B C B C D E F G H
Insertion
*Genes B and C were inserted into
the chromosome*
Insertion
c. Inversion - chromosome part breaks off and reattaches backwards
Inversion
A B C D E F G H A D C B E F G H
d. Translocation - chromosome part breaks off and adds to a different chromosome
Translocation
Inversion
InsertionDeletion
Translocation
C. Causes of Mutations
1. Spontaneous/Random mutations– ◦Some mutations just happen, ( amistake during
DNA replication, transcription, mitosis, meiosis). a. These lead to evolution.
2. Mutagen - Any agent that causes a change in DNA
a. Include radiation (uv or nuclear radiation) and chemicals (asbestos or formaldehyde)
B. Environmental agents