DNA + Genes

Ch5.3 – p174-181

I. Structure of DNA

A.) Chromosomes are made of proteins and DNA

i. Genes are sections of chromosome

ii. Genes are parts of DNA

iii. DNA in a chromosome is tightly coiled

B.) DNA is a macromolecule.

i. Scientists Franklin and Wilkins made and studied X-rays of DNA

i. Watson and Crick built the final model.

a.) The model showed how the smaller molecules bonded to form the double helix

Failed Models

C.) DNA is made of 4 nucleotides (A, T, G, C)

i. A nucleotide has 3 partsa.) nitrogen base

b.) sugar

c.) phosphate group

ii. The sugar and phosphate group form the sides of DNA, or “backbone”

iii. The nitrogen bases stick inwards like teeth on a zipper

iv. The nitrogen bases are:a.) Adenine (A)b.) Thymine (T)c.) Cytosine (C)d.) Guanine (G)

v. The nitrogen bases pair and form bondsa.) A – Tb.) C – G

II. DNA Replicates

A. During mitosis all chromosomes must be copied.

i. A strand of DNA will separate or “unzip”

ii. New nucleotides will bond with the exposed nitrogen bases

iii. 2 identical strands of DNA are produced

B. During replication…

* What is a code?

Codes use numbers, letters, or symbols to represent other information

III. Making Proteins

A. DNA codes for proteinsi. Most DNA is not part of any geneii. 97% of genes are non-coding or “junk DNA”iii. Junk DNA has functions other than protein buildingiv. DNA contains the information for all proteins in every

cellv. However, DNA cannot leave the nucleus

B. RNA is a nucleic acid that carries the code for making proteins from the nucleus to

the cytoplasm i. DNA cannot leave the nucleus

so RNA carries the messageii. RNA has a different sugar

group the DNAiii. In RNA the nucleotide uracil

(U) replaces thymine (T)a.) A – Ub.) C – G

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C. RNA’s role in the cell

i. There are 3 types of RNA:a. mRNA – transports messages from the

nucleus to the cytoplasm

b. tRNA – transports amino acids throughout the cell

c. rRNA – make up part of the ribosome

D. Making Proteins Step 1: Transcription

i. RNA is made from DNA

a.) process is similar to DNA replication

ii. RNA leaves the nucleus

E. Making Proteins Step 2: Translation

i. Occurs at the ribosome (free or rough ER)

ii. mRNA attaches to the ribosome

iii. tRNA which has an amino acid on its tail move to the ribosome

iv. rRNA connects the amino acids and the tRNA leaves

v. Repeats

Transcription

F. Codes

i. Proteins are made of amino acidsii. 3 bases on a tRNA codes for one

amino acidiii. A group of 3 nitrogen bases is

called a codoniv. 60 codons make 20 amino acidsv. Some codons do not add amino

acids but are start and stop signals.

IV. Most mutations occur during replication

i. Mutations can be triggered by x-rays, UV light, and chemicals

IV. Mutations

B. 3 Types of Mutations

i. Substitution a.) a base is replaced

ii. Insertion

b.) base pairs has been added

iii. Deletion

c.) base pairs has been removed

C. Results of Mutations

i. Some mutations are not negative (silent)a.) Don’t cause a change in the protein

ii. Some mutations change the protein and as a result change the trait