DNA Notes DAY 2
Replication, overview of transcription,
overview of translation
• WARM UP
• What is the base pairing rule?
• Who created it?
How DNA is Copied
• DNA is double stranded – base pairing allows
for easy copying; one strand serves as a
template for a new strand
• Replication – the process of making a new DNA
strand
• DNA double helix is unwound by an enzyme
called a helicase. Helicase breaks hydrogen
bonds linking the nitrogen bases
• The point where the helix separates is called the
replication fork.
• At the fork; enzymes called DNA polymerase moves
along the strands, reading the nitrogen base of each
nucleotide, and adds the complementary nucleotide to
the new strand
• DNA polymerase will proofread – it will only add a new
nucleotide if the previous one was added correctly
following the base pair rules
• Replication occurs in many places within the strand. It
does not start at one end and end at the other; but
occurs in segments
Steps for Replication
1. DNA helicase unzips the DNA by breaking the
hydrogen bonds holding the bases together
2. The two strands unwind creating a replication fork.
3. Each strand serves as a template so the correct pair
can come in and bind to the strands
4. DNA polymerase joins the nucleotides together and
proofreads the new strand. Proofreading improves the
odds of not having mistakes in the DNA
5. Two identical DNA molecules are made
The Path of Genetic Information
• Cells turn the information found within the genes on
DNA into a set of instructions for use in building
proteins.
• This set of instructions of the gene is called ribonucleic
acid or RNA.
• RNA is a single strand of nucleotides; DNA is double
stranded
• The sugar in RNA is a 5 Carbon sugar called ribose;
DNA’s sugar is deoxyribose
• RNA does not contain Thymine, but has replaced
Thymine with the base Uracil
DNA compared to RNA
How many
strands?
Nucleotide
subunit
Phosphate
Group
DNA
RNA
2
1
Deoxyribose
Sugar
Nitro
-gen
Base
phate
Nitro
-gen
Base
Ribose
Sugar
Group
Deoxyribose sugar
Bases
Phos-
Thymine (T)
Adenine (A)
Guanine (G)
Cytosine (C)
T–A
G–C
Ribose sugar
Uracil (U)
Adenine (A)
Guanine (G)
Cytosine (C)
U–A
G–C
There are 3 forms of RNA
1.
2.
3.
•
mRNA = messenger RNA
tRNA = transfer RNA
rRNA = ribosomal RNA
All 3 RNA’s are responsible for processing the
information in a gene into protein, this process is
GENE EXPRESSION
•
Gene expression occurs in 2 stages.
1. Transcription (RNA is made)
2. Translation (protein is made)
Transcription: Making RNA
• Transcription takes place inside the
nucleus
• RNA is made in the form of mRNA.
• It has a U (uracil) instead of T (thymine)
– A now pairs with U
• DNA: GAG AAC TAG TAC
• RNA: CUC UUG AUC AUG
Three Types of RNA
• mRNA – used as a blueprint or template
for a protein; carries DNA’s information to
site of translation
• tRNA – decodes mRNA into amino acid
sequences
• rRNA – RNA part of a ribosomes
structure.
The Genetic Code
• Instructions on mRNA are written as a
series of three nucleotide sequences
called a codon.
• Each codon (every three nucleotides)
corresponds to a certain amino acid or a
stop signal
• 64 possible codon combinations
Translation: Making Proteins
• Takes place in the cytoplasm
• mRNA carries the code so that proteins can be
made.
• tRNA tranlates that code and turns it into protein.
Genes and Proteins
• Genes contain nothing more than the
instructions for assembling proteins
• Proteins are the keys to almost everything that
living cells do
• Many proteins are enzymes which catalyze and
regulate chemical reactions
Examples of enzymes determining
characteristics
• An enzyme produces the
pigment that makes a flower
red
• An enzyme produces an
antigen on your red blood
cells determining your blood
type
• Enzymes control the growth,
shape, and size of your cells
Human Genome clip