Key Concepts: What forms the genetic code? How does a cell produce proteins? How can mutations affect an organism? Key Terms: Messenger RNA Transfer RNA
Key Concepts:
What forms the genetic code?
How does a cell produce proteins?
How can mutations affect an organism?
Key Terms:
Messenger RNA
Transfer RNA
Main function of genes is to control the production of proteins
Genes and DNA: Chromosomes are made of DNA.
Genes are sections of a DNA molecule that codes for one specific protein. May contain several hundred to a million or more base pairs (Ex. AGGTCACGAATTTTCCGG)
• The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.
• Proteins are made of amino acids – A group of 3 base pairs codes for a specific amino acid
• Ex. CGT = alanine (an amino acid)• The order of the 3 base code units determines
the order of the amino acids and makes the different proteins
The Role of RNA• Protein synthesis takes place on ribosome in
cytoplasm• RNA acts as a messenger to take the DNA’s
information in the chromosomes to the ribosomes in the cytoplasm
• RNA similar to DNA, yet different in some key ways:– single strand– ribose sugar– Bases – same - adenine, guanine and cytosine– different – uracil instead of thymine
Messenger RNA – copies code from DNA in the nucleus and carries message to ribosomes in the cytoplasm
Transfer RNA – carries amino acids to ribosome and adds them to the growing protein molecule
First Step:1. DNA molecule unzips between base pairs2. DNA directs the production of a strand of messenger RNA3. To form the RNA strand – RNA bases pair with DNA bases. Guanine with Cytosine, but uracil pairs with adenine instead of Thymine
Second step:1. Messenger RNA leaves nucleus and attaches to a ribosome in the cytoplasm2. Messenger RNA provides the code to make the protein molecule3. The ribosome moves along the messenger RNA strand
Third Step1. Molecules of transfer RNA attach to messenger RNA2. Bases of transfer RNA read the message by pairing up 3-letter codes to bases of messenger RNA3. Molecules of transfer RNA carry specific amino acids that link in a chain4. Order of amino acids is determined by order of 3-letter code on messenger RNA
Fourth Step1. Protein molecule grows longer as each transfer RNA adds an amino acid2. When done the transfer RNA is released into the cytoplasm and can pick up another amino acid3. Each transfer amino acid picks up the same type of amino acid
A mutation is any change in a gene or chromosome
Mutations can cause a cell to produce an incorrect protein during protein synthesis.
As a result of a mutation, the organism’s trait or phenotype, may be different from what it normally would have been
If a mutation is in a body cell, it will not be passed on to the offspring. If it is a sex cell, it can be passed on and can affect the offspring’s phenotype
Substitution Insertion
Deletion
Some mutations happen during DNA Replication:A single base may be substituted for anotherOne or more bases may be removed from a
section of DNA or new bases insertedSome mutations happen during Meiosis:Chromosomes don’t separate correctlyCell can end up with too many or too few
chromosomesCell could end up with fragments of
chromosomes
Mutations introduce change in an organism and so are a source of genetic variety
Some mutations are harmful, some are helpful, and some don’t affect the organism
Whether a mutation is harmful or not depends partly on the environment A mutation causing an albino
animal in the wild would be harmful, but if the animal lived in the zoo, it would not matter
Helpful mutations improve an organism’s chances for survival and reproductionEx. Bacteria that have mutations that have
given them resistance to antibiotics are more likely to survive and reproduce
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