Download - Protein Synthesis & Mutations
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Protein Synthesis &
Mutations
Chapter 13
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The Central Dogma of Biology:
Protein Synthesis
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RNA Structure:1. It is a nucleic acid.2. It is made of monomers called nucleotides3. There are two differences between a DNA
& an RNA nucleotide:- RNA has ribose instead of
deoxyribose- RNA has the base Uracil
instead of Thymine- Adenine will pair with Uracil
(Uracil is a pyrimidine)
Protein Synthesis
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Types of RNA:1. Messenger RNA (mRNA)
- carries the info from DNA to the ribosome - contains “codons” that code for individual amino acids
2. Ribosomal RNA (rRNA)- a component of the ribosome
3. Transfer RNA (tRNA)- “Transfers” the info on the mRNA to
an amino acid sequence (protein).- contains “anticodons” that
complement the codons on mRNA.
Protein Synthesis
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What is transcription?It is the process of making an RNA copy from a DNA template.
- All forms of RNA are made using this process.
- The process is similar to replication.
Protein Synthesis
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The Steps of Transcription:1. Initiation:
RNA polymerase binds to a location on the DNA called a promoter.
- Promoters signal the beginning of a gene.
- RNA polymerase has the ability to unzip the DNA.
Protein Synthesis
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The Steps of Transcription:2. Elongation:
RNA polymerase makes a complementary RNA strand from one of the exposed DNA strands.
- This DNA strand is called the “template strand.” (sense strand)
Protein Synthesis
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The Steps of Replication:
3. Termination:
RNA polymerase comes across a DNA sequence called a “terminator” and stops the transcription process.
Protein Synthesis
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Eukaryotic mRNA Transcripts must be edited.
1. The original mRNA contains sequences known as introns & exons.Introns = sequences that do not code for anything. Exons = sequences that actually code for a protein.
2. The introns are cut out and the exons are spliced together.
3. A cap sequence & a tail sequence are added and the mRNA is ready to go.
Protein Synthesis
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The Genetic Code:1. The sequence of the DNA bases “codes” for the
individual amino acids in a protein.2. This code is copied on to an mRNA strand.3. The mRNA code:
- 3 mRNA bases in a row are called a codon & each codes for a particular amino acid.
4. Because there are 4 RNA bases, there are 64 different
3-base combinations (104 = 64).- One combination is known as the “start codon” (AUG). This marks the beginning of the protein.- Three of them are “stop codons” (UAA, UAG, UGA). These codons do not code for any amino acids, thus signaling the end of the protein.
Protein Synthesis
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What is the amino acid sequence from the following mRNA sequence?
AUGGUCGAUAAACCACGCCUGUGAMet-Val-Asp-Lys-Pro-Arg-Leu
Protein Synthesis
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What is Translation?Process in which a ribosome reads the mRNA & makes a protein (polypeptide).
Ribosome Structure:1. Has two subunits: small & large2. Large subunit has two sites:
p site (polypeptide site) a site (amino acid site)
Protein Synthesis
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Translation Animation
Protein Synthesis
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What is a mutation?Any kind of change to the base sequence of either DNA or RNA.
- Mutations cause the amino acid sequence to be incorrect.
- An incorrect amino acid sequence usually causes the protein to be nonfunctional or it gives the protein new functions.
Mutations
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1. Gene Mutations (a.k.a. point mutations)These affect a particular gene only.A. Substitution – replace one base with another. - affects only one amino acid in the protein. - May not even cause a problem (silent mutation). B. Insertion – a new base is placed in the sequence; this alters the reading frame & every amino acid after the mutation is altered.C. Deletion – a base is removed & every amino acid after this mutation is altered.
Insertions & deletions are called frameshift mutations.
Types of Mutations
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2. Chromosomal Mutations – affect whole chromosomesA. Deletion – part of the chromosome disappearsB. Duplication – part of the chromosome is copied.C. Inversion – the sequence of genes on the chromosome is partially flipped.D. Insertion – part of one chromosome is removed an placed onto a different chromosomeE. Translocation – parts of two chromosomes are clipped off and they switch places.
Types of Mutations