Download DNA_2007

DNA
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DNA
Deoxyribonucleic
Acid
It
is the main component of your
chromosomes
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DNA is a Double Helix
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Helix = Spiral
DNA is a
Twisted Ladder
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Nucleic Acids (sides of the ladder)
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Alternates sugars (deoxyribose) and Acids
(phosphate group)
The bases (steps in the ladder) attach to
the sugars
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DNA facts
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Watson and Crick discovered the double
helix model
The only differences in DNA of living
things is the length and order of the bases
The 4 Nitrogen Bases
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A=Adenine
T=Thymine
C=Cytosine
G=Guanine
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Base Pairs
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The bases join together in Complementary
Base pairs
They are the rungs of the ladder
Complementary Base Pairs:
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A connects to T
C connects to G
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Base Pairs
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What is the complementary side to this
sequence of base pairs?
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ATAACGGCA
TATTGCCGT
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DNA structure
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How DNA works
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We use 26 different letters and short sentences to
“code” the English language
DNA uses 4 different bases and “sentences” that
are thousands of bases long to “code” genetic
messages
The order of the bases determine the coded
message
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How DNA works
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If chromosomes are the instruction books,
Genes are the chapters,
DNA strands are the sentences
Codons (3 bases) are the words,
Nitrogen Bases (A, T, C, G) are the letters
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How the DNA makes proteins
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Ribosomes make proteins; found in
cytoplasm
DNA never leaves the nucleus
DNA has a helper molecule: RNA
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Ribonucleic acid
RNA is a chemical that acts as a
messenger for DNA to carry messages to
the ribosomes
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4/18/08 Transcription &
Translation Notes
RNA
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Only has 1 side of the ladder
The sugar is Ribose (not Deoxyribose)
No T (thymine). Has U (uracil) instead
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UAAGCGUA
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3 types of RNA
1. rRNA=Ribosomal RNA
2. mRNA=Messenger RNA
3. tRNA=Transfer RNA
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rRNA
construction worker – builds the protein

The main component of ribosomes
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mRNA
Messenger – brings copies of information from
DNA (stored in nucleus) to the ribosomes
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tRNA
Transfer – delivers building material (amino acids)
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The main coding component is 3 RNA bases
deliver specific materials depending on the
order of the bases
Carries specific amino acids to the
ribosomes depending on what 3 bases they
have
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(amino acids are building blocks of proteins)
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the path from genes to proteins
has two steps
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TRANSCRIPTION
TRANSLATION
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Transcription:
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DNA partially ‘unzips’
mRNA recodes part of the message into
Complementary RNA language (Uses Uracil
instead of Thymines)
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DNA: ATAACGGCA
RNA: UAUUGCCGU
DNA rezips while mRNA moves into the cytoplasm
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http://bcs.whfreeman.com/thelifewire/content/chp12/1
202001.html
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Translation:
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mRNA finds ribosome
mRNA is “read” 3 bases at a time (codon)
Complementary tRNA molecules transport
Amino Acids to the ribosomes where they
are put together in the coded order to
form proteins
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Translation/Protein Synthesis:
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START codon (mRNA): AUG
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tRNA UAC carries Methionine (Met) to start
every protein
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STOP codons (mRNA): UAA, UAG, etc.
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http://bcs.whfreeman.com/thelifewire/content/chp12/1202003.html
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DNA Synthesis
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Chromosomes copy (replicates)
themselves before mitosis & meiosis
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During S-Phase
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Steps in DNA Replication
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DNA separates in the middle of the ladder
Loose bases without a pair will join the
complimentary base to make pairs
After they join, you have 2 DNA molecules
(2 ladders)
The 2 DNA are exactly alike
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Quick Quiz
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What are the 4 base pairs?
What does DNA stand for?
What does RNA stand for?
What does RNA do in the making of
proteins?
What makes the proteins?
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