Chapter 11DNA and Genes

•Proteins

•Form structures and control chemical reactions in cells.•Polymers of amino acids.•Coded for by specific sequences of nucleotides in DNA.

•Exons

•Regions of genes that contain information.

•Introns

•Long noncoding nucleotide sequences located in genes.

•RNA

•Nucleic acid.•Single stranded.• Formed from a phosphate group, the sugar ribose, and four nitrogenous bases (adenine, guanine, cytosine, and uracil).

•Transcription

•Process where enzymes make an RNA copy of a portion of a DNA strand.

•RNA and Protein Synthesis

•RNA uses the instructions provided by DNA to assemble proteins, amino acid by amino acid.

•Translation

•Takes place at the ribosomes.•The process of converting the information in mRNA into a sequence of amino acids in a protein.

•Three Types of RNA

1. Messenger RNA2. Ribosomal RNA3. Transfer RNA

•mRNA

•Brings instructions from DNA in the nucleus to ribosomes located in the cytoplasm where protein synthesis occurs.

•mRNA

•Uses a combination of three nitrogenous bases, called a codon, to code for one of 20 common amino acids.• There are 64 codons possible.• Some codons code for instructions such as start (AUG) and stop (UAA).• The same amino acid can have more than one codon.

•mRNA

•During transcription, both introns and exons are copied. •However, the introns must be removed from the mRNA by enzymes and the resulting exon pieces pasted back together before it the mRNA can move out of the nucleus and function to make a protein.

•rRNA

•When mRNA reaches the ribosome, rRNA binds to the mRNA and uses the instructions provided to assemble the amino acids in the correct order.

•tRNA

•Delivers amino acids to the ribosome where they are assembled into proteins.•Each tRNA molecule attaches to only one type of amino acid.

•tRNA

•A sequence of three nucleotides, called an anticodon, is located on the side of the tRNA opposite the amino acid attachment site.•The anticodon of the tRNA binds to the correlating codon on the mRNA, insuring correct translation of the mRNA message.

•Steps in Translation

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•Steps in Translation

1. A tRNA molecule brings the first amino acid to the mRNA strand which is attached to a ribosome.

2. The anticodon of the tRNA forms a base pair with the corresponding codon of the mRNA.

3. The ribosome slides down the mRNA chain to the next codon.

•Steps in Translation

4. A new tRNA molecule carrying a second amino acid pairs with the new codon.

5. The two amino acids that are now adjacent to each other form a bond.

6. The first tRNA releases its amino acid and detached forms the mRNA, in order to bring another amino acid to the chain.

•Steps in Translation

7. The ribosome slides down to the next codon and the previous steps are repeated.

8. This process continues, forming a chain of amino acids, until a stop codon is reached, where translation ends and the amino acid chain is released form the ribosome.

•Steps in Translation

9. Amino acid chains become proteins when they are freed from the ribosome and twist and curl into complex 3-D shapes.• Each protein chain forms the same

shape every time it is produced.