Tuesday Novermber 29, 2011

This is the process of DNA becoming tRNA.

1. DNA Replication- Before a cell divides, it must first duplicate its DNA- replication


2. Transcription- A molecule of DNA is copied into a complementary strand of mRNA


3. Translation- tRNA anticodons (3 nucleotides) complement the mRNA and bring in the corresponding amino acids


4. Protein Synthesis- Amino acid are bonded together to form a polypeptide

RNA has-

1. ribose sugar



2. 1 strand



3. Uracil instead of Thymine



4. smaller size than DNA- can go inside/outside nucleus



5. 3 types- messenger- mRNA, transfer- tRNA, ribosomal- rRNA(its the one that form ribosomes)

Steps of Transcription

1. Initiation- RNA polmerase attaches to the DNA promoter nucleotide sequence on DNA. RNA is synthesized

2. RNA elongation- RNA grows longer, peels away from DNA, DNA strands come back together (uses DNA as a template)

3. Termination- RNA polymerase reaches the terminator- end of the gene. polymerase molecule detaches from RNA molecule and the gene

Processing RNA

in prokaryotes, RNA is ready(mRNA)

in eukaryotes, it needs to process it, add extra nucleotides

• cap and tail protect RNA from enzymes and help ribosomes recognize it as mRNA



• introns-non coding regions (useless junk)



• exons-are the coding regions

introns are removed before RNA leaves the nucleus=RNA splicing

• mRNA is now ready

Steps of Translation

1. initiation-

• a mRNA binds to small ribosomal subunit. tRNA with attached amino acid (Met) (UAC) binds to start codon, AUG on mRNA



• large ribosomal subunit binds to small one, creating a functional ribosome

2. elongation- amino acids are added one by one to the first amino acid

3. a stop codon (UGA, UAG, UAA) does not code for an amino acid. tells translation to stop. Polypeptide is freed ( several hundred amino acid) ribosome splits into its subunits

Review

DNA->RNA->Protein. genes determine the protein, which makes your appearance and your cell capabilities

1. Mutations

• change in nucleotide sequence of DNA-a. base substitution- replacement of one base for another. no change, or critical, bad or good~b. base insertion or deletions- adding or subtracting nucleotides. often disastrous results- can disrupt entire sequences of triple pairing (insertions are always bad)



• mutagens- physical and chemical agents, such as UV light, x-rays, chemicals, carcinogens. can cause mutations. Can also lead to diversity. DNA errors are also due to unknown causes.

next scribe Dana