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 – deoxyribose
2.
Phosphate group – 1 P with 4 O’s
3.
Nitrogen base (4 kinds)
Nitrogenous
base
Phosphate
group
Sugar (deoxyribose)
B.
Adenine (A)
C.
Nitrogen Bases:
Guanine (G)
Cytosine (C)
Thymine (T)
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
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.
DNA rap
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
III.
RNA (Ribonucleic Acid – 3 types) – a 1-chain
polymer of nucleotides made from 2-chained
DNA that helps to make proteins
Uracil
A.
Adenine
Nucleotides have 3 parts:
1.
Sugar – ribose →
2.
Phosphate group – 1 P with 4 O’s
3.
Nitrogen base (4 kinds: A, C, G, U)
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.
2.
3.
4.
Double-stranded DNA is “unzipped” in the
nucleus
An enzyme, RNA polymerase, binds to a specific
section of DNA where mRNA will be made
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)
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.
D.
mRNA begins translation with an AUG
“start” codon. tRNA brings the amino acid
Methionine to begin the protein
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)