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DNA AND PROTEIN SYSNTHESIS
DNA PROTEIN
What structures are found in the nucleus?
What is a gene? • Gene: a portion of DNA that contains
the codes (instructions) for one protein.
GENE
• A gene is a sequence of nucleotides that has the code (instructions) for making a specific protein
• The average gene is 3000 bases
• Total number of genes is 30,000 to 35,000
Protein Synthesis
The building of proteins from amino acids
• Why are proteins important?
–Make up important structures like muscles and cell membranes.
– Substances like enzymes, antibodies and hormones are made of proteins
– Traits like hair and eye color are the results of proteins
RIBOSOME
Where is DNA?
Where are proteins made? ribosome
• Where are proteins synthesized ?
By the ribosomes
In the cytoplasm.
• What are proteins made of?
–Proteins are long chains of amino acids
– There are 20 different amino acids
• The instructions for making proteins
(the order of the amino acids in a particular protein)
are encoded in the DNA
(the code)
CODON • Codon – a set of
three nitrogenous bases that represents an amino acid
Codon
• The bases are arranged in threes called codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C
Protein Synthesis takes
place in 2 stages
transcription
translation
RNA • RNA
– Ribonucleic acid
– RNA is similar to DNA but is single stranded
– RNA contains the sugar ribose (not deoxyribose)
– The nitrogen base uracil replaces thymine
Three Types of RNA • Messenger RNA
(mRNA)
– Is formed in the nucleus
–Carries the instructions from the DNA in the nucleus to the ribosomes in the cytoplasm
–“The Messenger”
CODON • Order of nitrogen
bases in mRNA that determines the type and order of amino acids in a protein
• mRNA has the CODON!
• There are 64 possible codons, but only 20 amino acids to code for
TRANSFER RNA • Transfer RNA (tRNA)
– Carries amino acids from the cytoplasm to the ribosome.
–Has the anticodon
– “The Worker”
RIBOSOMAL RNA (rRNA)
– The ribosome is made of rRNA.
Transcription
• During the production of proteins the “blueprints” (instructions) are located in the nucleus, in a code in the DNA
• DNA acts as a template for making messenger RNA
Complementary base pairing
DNA Base Complementary RNA
Base
G
C
A
T
C
G
U
A
Transcription
• mRna picks up the triplet code from the DNA
• m RNA leaves the nucleus.
• A ribosome attaches to the mRNA.
• The instructions carried by the mRNA will be used to assemble the amino acids in the proper order
•The instructions (codon) are
then carried to the cytoplasm
Translation
• The amino acids are brought to the ribosomes by the tRNA molecules to be assembled into a protein (translation)
• The order of the amino acids is determined by the codon on the mRNA
Protein Synthesis • The tRNA
anticodon pairs with the mRNA codon
• The tRNA releases the amino acid which bonds to the other AA ‘s forming a chain = protein
MUTATIONS
Mutations • If DNA is not copied exactly, proteins
made from its instructions could be made INCORRECTLY
• Mutation: any permanent change in the DNA sequence in a gene or chromosome.
• Factors that cause mutations: X rays, sunlight, and some chemicals
Results of a Mutation
• Genes control the traits you inherit.
• Without correctly coded proteins, an organism can’t grow, repair, or maintain itself.
• A change in a gene or chromosome can change the traits of an organism.
Results of a Mutation
• If the mutation occurs in a body cell, it might not be life threatening to the organism.
• If a mutation occurs in a sex cell, then all the cells that are formed from that sex cell will have that mutation.
Results of a Mutation
• Many mutations are harmful to organisms, often causing their death.
• Some mutations do not have any effect on the organism.
•Some mutations can be helpful and
give the organism a better chance of
surviving.
DNA and Mutations –
Lets looks at different mutations
THE DOG BIT THE CAT
Mutations - Substitution
THE DOG BIT THE CAT
• Substitution - Replace just one letter:
THE DOG BIT THE CAR
Deletion
THE DOG BIT THE CAT
• Deletion: Delete just one letter (T):
THE DOG BIT HEC AT
Insertions
THE DOG BIT THE CAT
• Insertion - Add just one letter (E):
THE DOE GBI TTH ECA T
Cells have “proof reading” proteins that
constantly check the DNA and fix errors, so most
are corrected
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