Chapter 12.1 – DNA Structure

I. DNA (Deoxyribonucleic Acid) – a 2-chain polymer of nucleotides that we inherit A. Nucleotides have 3 parts:

1. Sugar – deoxyribose2. Phosphate group – 1 P with 4

O’s3. Nitrogen base (4 kinds)

Phosphate group

Sugar (deoxyribose)

Nitrogenous base

B. Nitrogen Bases:

C. Arrangement of Nucleotides:1. Phosphate groups and

Deoxyribose sugar molecules form the backbone of the DNA “ladder,” by alternating

2. Nitrogenous bases face inward, like the rungs of a ladder

Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

II. The Structure of DNA A. Nitrogen bases hold the “rungs” of

the DNA ladder together, forming the shape called a double helix

1. A & T pair, with 2 hydrogen bonds

2. G & C pair, using 3 hydrogen bonds

Thus, the 2 strands of DNA are complimentary

B. Each strand has a 5’ and 3’ end, but they run in opposite directions (antiparallel)

C. Nucleotide sequences are important!

1. All living organisms have deoxyribose sugars,

phosphate groups, and nitrogen bases like A, G, C, and T in their DNA

It is the sequence of the bases that make us all different from each other

2. Sequences can be used to determine:

if 2 organisms that look alike from different continents are related

if 2 people are related body identification at crime

scenes

DNA rap

III. RNA (Ribonucleic Acid – 3 types) – a 1-chain polymer of nucleotides made from 2-chained DNA that helps to make proteins

A. Nucleotides have 3 parts:1. Sugar – ribose →2. Phosphate group – 1 P with 4

O’s3. Nitrogen base (4 kinds: A, C,

G, U)

Uracil Adenine

Chapter 12.3 – DNA, RNA, & Protein

I. The Central Dogma: DNA codes for RNA,RNA guides the synthesis of

proteins A. Types of RNA

1. Messenger RNA (mRNA) – long strand of RNA nucleotides

that are formed complimentary to one strand of DNA

2. Ribosomal RNA (rRNA) – associates with proteins to form ribosomes in the cytoplasm

3. Transfer RNA (tRNA) – smaller segments of RNA that

transfer amino acids to the ribosome

B. Transcription – synthesis of mRNA from DNA

During this process, the DNA code is transferred to mRNA in the nucleus.

The mRNA can then take the code into the

cytoplasm for protein synthesis.

1. Double-stranded DNA is “unzipped” in the nucleus

2. An enzyme, RNA polymerase, binds to a specific section of DNA where mRNA will be made3. RNA polymerase starts making mRNA from one strand of DNA, known as the template strand

DNA is read in the 3’ to 5’ direction The mRNA strand is complimentary to

the DNA template strand, and is made 5’ to 3’

Uracil (U) is used instead of Thymine (T)4. Eventually, mRNA is released. It will move from the nucleus, through nuclear pores, to the cytoplasm

III. Translation – codons form a “3 base” code to translate mRNA into a protein

A. mRNA arrives in the cytoplasm, at a ribosome

B. tRNA molecules act as interpreters of the mRNA codon sequence

tRNA forms a cloverleaf shape and contains an anti-codon

C. mRNA begins translation with an AUG “start” codon. tRNA brings the amino acid Methionine to begin the proteinD. Translation continues by adding and

linking amino acids in the sequence determined by the mRNA, until a

“stop” codon is reached (UAA, UAG, or UGA)