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)