Download DNA = DEOXYRIBONUCLEIC ACID

DNA = DEOXYRIBONUCLEIC ACID
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blueprint of life (has the instructions for making an organism)
established by James Watson and Francis Crick
codes for your genes
shape of a double helix
made of repeating subunits called nucleotides
Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye
color..etc), a gene is a stretch of DNA.
Nucleotide - consists of a sugar, phosphate and a base
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Nucleotides (also called Bases): Adenine, Thymine, Guanine, Cytosine or A, T, G, C
Nucleotides pair in a specific way - called the Base-Pair Rule:
Adenine pairs to Thymine
Guainine pairs to Cytosine
*The rungs of the ladder can occur in any order (as long as the base-pair rule is followed)
How the code works
For instance, a stretch of DNA could be AATGACCAT - which would code for a different gene than a
stretch that read: GGGCCATAG. Those 4 bases have endless combinations just like the letters of
the alphabet can combine to make different words.
DNA REPLICATION
Replication is the process where DNA makes a copy of itself. Why does DNA need to copy? Simple:
Cells divide for an organism to grow or reproduce, every new cell needs a copy of the DNA or
instructions to know how to be a cell. DNA replicates right before a cell divides.
DNA replication is semi-conservative. That means that when it makes a copy, one half of the old
strand is always kept in the new strand. This helps reduce the number of copy errors.
RNA = Ribonucleic Acid
DNA remains in the nucleus, but in order for it to get its instructions translated into proteins, it must
send its message to the ribosomes, where proteins are made. The chemical used to carry this
message is Messenger RNA (mRNA).
RNA is similar to DNA except:
1. has on strand instead of two strands.
2. has uracil instead of thymine
3. has ribose instead of deoxyribose
mRNA has the job of taking the message from the DNA to the nucleus to the ribosomes.
Transcription - RNA is made from DNA
Translation - Proteins are made from the message on the RNA
Gene Expression
Three Important Points to Remember
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Chromosomes are made of DNA
Segments of DNA code for a protein
Protein in turn, relates to a trait (eye color, enzymes, hormones, etc)
How are Proteins Synthesized from DNA
1. DNA is transcribed into mRNA (messenger RNA)
2. mRNA leaves the nucleus and travels to the cytoplasm
3. Ribosomes in the cytoplasm use the code on mRNA to translate it into amino acids
4. Amino acids form a chain - a protein
Sounds simple, huh? Well, you're not getting off that easy, now we will break down each step of the
process.
Transcription
Animation of Transcription: http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
RNA is very similar to DNA with the following exceptions:
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it is single stranded
it has uracil instead of thymine
it has the sugar ribose, instead of deoxyribose
The base-pair rule is followed during transcription, except, instead of pairing thymine with adenine,
when creating an RNA strand, uracil is used
DNA Strand: T G C A T C A G A
RNA Strand: A C G U A G U C U
Transcription begins on the area of DNA that contains the gene. Each gene has three regions:
1. Promotor - turns the gene on or off
2. Coding region - has the information on how to construct the protein
3. Termination sequence - signals the end of the gene
RNA Polymerase is responsible for reading the gene, and building the mRNA strand. It reads only
the 3' to 5' strand.
Still confused: Check on these animations:
http://www.ncc.gmu.edu/dna/mRNAanim.htm
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
Translation
Animation of translation: http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html
1. The mRNA travels to the cytoplasm
2. Amino acids exist freely in the cytoplasm, many of them
you acquire from your diet
3. Each 3 bases (codon) translates to a single amino acid.
4. The ribosome looks for the "start" codon - AUG, this is
where the chain begins
5. Transfer RNA (tRNA), has an anticodon at one end and
an amino acid at the other, it binds to a complementary
codon.
6. Another tRNA reads the next codon, the amino acid
attached to it binds with the amino acid on the previous
tRNA using a peptide bond. The first tRNA falls off.
7. This process continues until the "stop" codon is
reached.
8. The amino acid chain folds into a 3 dimensional
structure, now a protein.
9. That protein can be an enzyme, a hormone, or any other
structure in the body that gives it traits and functionality.
Still confused?
Check out other animations:
http://www.cat.cc.md.us/biotutorials/protsyn/translat.html
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf
Test for Understanding
A DNA sequence has the following bases: T A C - A G A - T T A - G G G - A T T
What amino acids does it code for?