Chap. 12DNA & RNA

I. 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?

•Ribonucleic Acid•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.

•5) mRNA leaves the nucleus thru nuclear pores and enters cytoplasm.

•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 UCGCACGGUcodons 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 themessages

•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. 12-205. What happened in:

1. Deletion…2. Duplication…3. Inversion…4. Translocation…