Transcript Chapter 12 DNA - Mr. Tate's Biology Site

Cells Lecture IV
DNA and Protein Synthesis
Biology Standards Covered
• 1d ~ students know the central dogma
of molecular biology outlines the flow of
information from transcription of
ribonucleic acid (RNA) in the nucleus to
translation of proteins on ribosomes in
the cytoplasm
The Structure of DNA
• DNA is a long
molecule made
up of nucleotides
• Each nucleotide is
made up of three
parts:
– 5-carbon sugar
called
deoxyribose
– Phosphate group
– Nitrogen Base
The Nucleotides
Nitrogen Bases
A- adenine
G- guanine
Adenine Guanine
Cytosine Thymine C- cytosine
T- thymine
Phosphate group
(Deoxyribose)
5-Carbon Sugar
Chargaff’s Rules
• According to Erwin Chargaff:
– Adenine always pairs with Thymine
– Cytosine always pairs with Guanine
The Double Helix
Nucleotide
Hydrogen
bonds
Sugarphosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine(C)
Guanine (G)
• base pairing- hydrogen bonds forming only
between certain “base pairs”
DNA Arranged in a
Chromosome
Central Dogma
• The term central dogma is used in science
to describe the “making of proteins” from
instructions coded in the DNA
• An equation to remember for Central
Dogma would be:
DNA
mRNA
Amino Acid Chain
Transcription
Translation
Transcription inside the Nucleus
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
DNA
Transcription
• Promoters – specific sites where the
enzyme-protein RNA Polymerase
binds to the strand of DNA to begin
transcription
Central Dogma
• Proteins are assembled into polypeptides
– These are long chains of amino acids
– There are 20 different types of amino
acids
– The properties of proteins are
determined by which order these
amino acids are joined
Central Dogma
• Each of these amino acids that mRNA “codes”
for recognizes the three base pair sequence
• A codon consists of “three nucleotides in a
row” that code for a single amino acid
– AUG codes for the amino acid Methionine
The (20) Amino Acids
Methionine is the
universal “start
codon” for all
proteins
Central Dogma
•Along with the twenty amino acids there
are “special” base pair sequences that
“code for” start and stop codons
•Stop codons are like the “period at the
end of a sentence”.
– They signify the end of a polypeptide
(amino acid chain)
The (20)
Amino
Acids
Translation
• The term central dogma is used in science
to describe the “making of proteins” from
instructions coded in the DNA
• An equation to remember for Central
Dogma would be:
DNA
mRNA
Amino Acid Chain
Transcription
Translation
Translation
Nucleus
Phenylalanine
Methionine
Lysine
tRNA
mRNA
Transfer RNA
Ribosome
mRNA
Start codon
Translation
• Each strand of mRNA is separated into three
base pairs called codons
• AUG —- UUC --- AAA (mRNA)
• This is where transfer RNA comes in (tRNA)
Translation
• tRNA is responsible for getting the right
anticodon with each of the mRNA codons
• An amino acid is attached to each
anticodon
Lysine (Amino Acid)
tRNA
Ribosome
mRNA
Translation
The Polypeptide “Assembly
Line” The ribosome joins the
two amino acids & breaks the
bond between the tRNA & it’s
amino acid
Lysine
Growing polypeptide
chain
Ribosome
tRNA
tRNA
mRNA
mRNA
Ribosome
Translation
direction
Completing the
Polypeptide
The process continues until the
ribosome reaches one of the three
stop codons. The result is a
growing polypeptide chain.