Notes: Chapter 13: RNA & Protein Synthesis

1. Notes: Chapter 13: RNA & Protein Synthesis • 2 steps: • Transcription (DNA is made into mRNA in the nucleus) • Translation (mRNA is made into proteins by ribosomes in the cytoplasm or ER)

2. RNA Structure • Similar to DNA, but with some important differences: • Single strand (DNA double) • Ribose is the sugar (not deoxyribose like DNA) • Uracilmatches adenine (instead of thymine like DNA) • Shorter than DNA

3. RNA Functions • Three different types of RNA: • mRNA (messenger) used as template to make proteins • rRNA(ribosomal) makes up ribosomes • tRNA(transfer) matches amino acids to mRNA to help make proteins

4. Transcription • transcribe(to copy) • happens in the nucleus • DNA’s code is copied onto RNA • 1. RNA polymerase binds to beginning of a gene (promoter) and unwinds DNA • 2. Complementary bases copied from 1 sideof DNA • 3. Termination (end) signal reached, mRNA and DNA free • http://www.youtube.com/watch?v=ztPkv7wc3yU

5. Translation • RNA’s “language” is translated into amino acids (which will become a protein) • RNA’s language is set of three nucleotides called a codon…3 nitrogen bases in a row • Codonsmatch with specific amino acids to make polypeptide chain (which will be modified to make a protein) • 20 amino acids all together • More than 20 codons, so some amino acids have more than one codon. There is also 1 start codon and 3 stop codons.

6. Translation

7. Translation 1. ribosome attaches to mRNA 2. tRNA with amino acid matches mRNA codon(area on tRNA that matches called an anticodon). This process is called initiation. 2 tRNAs can fit at one time. 3. ribosome moves down and matches next codon. 4. Amino acids form peptide bond and protein continues to grow, 1 amino acid at a time. This process is called elongation. 5. ribosome reaches stop codon, mRNA, tRNAs, protein and ribosome released. This process is called termination. The product is called a polypeptide. Modified in ER or Golgi to make a protein.

8. Translation • Each mRNA can be used more than once, by more than 1 ribosome at a time, so many proteins can be translated from 1 transcribed piece mRNA. • http://www.youtube.com/watch?v=-zb6r1MMTkc

9. Gene expression • The whole process of going from DNA to RNA to a protein that runs a cell process is called gene expression

10. Gene expression • After the polypeptide chain is made, it is often modified in the ER or Golgi Apparatus • The finished product is a protein and it has a three dimensional shape that decides its function

11. Mutations • Certain things can cause changes to the DNA/RNA code. They are called mutagensand cause mutations. • e.g. UV light, smoking, X rays, exposure to chemicals • Not all are bad…some allow for adaptation and evolution

12. Point mutations • Occur to one base or a small number of bases on DNA or RNA • Most are harmless, as many codons often code for the same amino acid. • 3 kinds: • Substitution: one base is used instead of another • Insertion*: one base is added • Deletion*: one base is left out • * lead to a frameshift mutation, where everything is “off by one” base.

13. Point mutations

14. Chromosomal mutations • Change to a gene, series of genes or an entire chromosome • These are often helpful in plants, e.g. polyploidy…chromosomes do not separate during meiosis. Leads to seedless fruit that are bigger • In animals, they are often harmful or even lethal. You might be researching one disorder in the next unit on genetics…

15. Chromosomal mutations • Deletion: one or more genes is/are left out when copied • Duplication: one or more genes is/are copied more than once • Inversion: one or more genes is/are copied backwards • Translocation: one or more genes is/are moved from 1 chromosome to another • Nondisjunction (not shown): homologs fail to separate during meiosis

17. Transcription