DNA - What is it? • It’s the molecule that makes- up the genetic code. • Polymer of double-stranded nucleotides
Chromosome structure: (P. 297) • DNA + histones = chromatin • histones + chromatin = nucleosome • nucleosome allow lots of DNA to fit into a tiny space!! • Like a tape measure!
Made of: • 1) deoxyribose sugar • 2) phosphate group • 3) Nitrogen base – which are • A)purines • Adenine & Guanine & • B)pyrimidines • Cytosine & Thymine
The bases bond in a special arrangement. • A bonds with T • G bonds with C • These bonds are called complimentary bases. (At The Girl’s Club!!)
Major functions of DNA: • Replication – “makin’ copies” & • Protein Synthesis – “tellin’ the cell what to do!”
II. A. Replication • Process to make a copy of the DNA. Both strands of DNA act as a pattern for the new DNA strands.
B. Steps: (inside the nucleus) • 1. Bonds between bases weakened & strands “unzip”.
2. The exposed bases bond with their complimentary bases found “floating” in the nucleus.
3. Sugar-phosphate bonds link. • This links the nucleotides together.
III. A. How does this info (inside the nucleus) get outside to “boss” the cell around?” • By using….mRNA – messenger RNA • It takes the message outside to the ribosomes.
B. What is RNA? • RibonucleicAcid • There are 3 types of RNA. • It controls the synthesis of proteins. • Polymer of single-stranded nucleotides
C. Made of: 1) ribose (5 - C sugar) 2) the nitrogen base Uracil (replaces Thymine) 3) phosphate group
D. Transcription – “Cross writing” • uses mRNA to write a message so the ribosomes understand “what to do”
E. STEPS IN MAKING mRNA: 1) Enzymes separate DNA strands 2) Complimentary bases attach to exposed ends. “Uracil replaces Thymine”
3) Enzymes bond sugar- phosphates molecules • 4) Bonding continues until the end.
Nucleotides are “read” as a set of three called a codon. • Codons “carry” specific amino acids. • Certain codons mean start & others mean stop.
For example… mRNA is UCGCACGGU codons are UCG – CAC – GGU P. 303 Fig. 12-17 – be able to identify the amino acids Amino acids are Serine – Histidine - Glycine
QUICK LAB - P. 303 • RIGHT MARGIN • WRITE ANSWER IN ON A SEPARATE PAGE! • ANSWER #1 THRU #4 • A & C #1 ONLY
IV. Translation – Interpreting the message to make proteins • Uses tRNA that float around in the cytoplasm.
A. Made of: • An anticodon on one end - 3 nitrogen bases that bond to the codon, • And its specific amino acid on the other end.
B. Steps in translation: • 1) mRNA connects to a ribosome at the start codon (AUG) • 2) ribosome “reads” the codon & identifies the anticodon. • (EX. codon AUG is with anticodon UAC)
3) rRNA (inside the ribosome) bonds the tRNA to its mRNA • 4) tRNA attaches its amino acid synthesizing specific proteins.
5) Peptide bonds unite the amino acids. • 6) This process continues until it reaches a stop codon
The order of amino acids is very specific for proteins. • Enzymes, specific biomolecules…
SO… • DNA has the “message” that is replicated for all new cells. • The message is sent out into the cells by transcription. • Proteins are assembled by translating the message.
V. Mutations…. • … are “errors” in the messages • They could be harmful/lethal/ no affect
Point mutations occur at one point in the DNA sequence. (P. 307) • Could be substitution, insertion or deletion of a nucleotide. • This is a frameshift mutation
Chromosome mutations affect the entire chromosome • Could be deletion, inversion, duplication, or translocation
More mutations: • Somatic cells mutations may affect only the individual • Sex cell mutations may affect offspring/children
Figure Questions – P. 307 • 1. Describe what happened in the 1st box. • 2. What is the effect on the amino acid sequence? • 3. What happened in box 2? • 4. And the effect on the amino acid sequence?
P. 308 Fig. 12-20 • What happened in: • Deletion… • Duplication… • Inversion… • Translocation…