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Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
Date: October 29, 2007
Drill
Where do Transcription and Translation occur?
Nucleus DNARNA
What are Transcription and Translation doing?
Ribosome RNAAmino Acids
1. Transcription
1. Occurs in the nucleus
2. Using DNA to make mRNA
Transcription: production of mRNA copy of the DNA gene.
Gene: Section of DNA within a chromosome that codes for the synthesis of one protein. There are roughly 20-30,000 genes on the 23 pairs of
human chromosomes.
Only 1 side of DNA in a gene gets transcribed:
A. Sense Strand: Strand of DNA in a gene which has the same nucleotide sequence as the m-RNA (except with T instead of U).
Translation: synthesis of protein by ribosomes
Anticodon: the 3 nucleotide sequence on t-RNA which the ribosome must fit against m-RNA to ensure that the correct amino acid is placed in
the growing protein during translation.
Initiation: Initiates translation. rRNA polymerase of ribosome binds to mRNA strand. 1st tRNA is bonded to mRNA.
Elongation: Ribosome reads mRNA chain in three nucleotide groups (codon) & inserts 2nd tRNA.
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
tRNA anti-codon (with amino acid) binds to mRNA codon
Translocation: 5' to 3' sequence continues building amino acid polymers (protein), one codon at a time.
Termination: tRNA recognizes release factors of nonsense codon. Newly completed polypeptide is released from ribosome
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/transcription.gif
In translation, the mRNA strand created in transcription is read and translated into a protein. The mRNA
binds to a ribosome, a large organelle found in the cytoplasm. The strand of mRNA is pulled through the
ribosome three bases at a time. Each of these triplets on the mRNA strand is called a codon. Another
type of RNA, transfer RNA (tRNA), reads the strand of mRNA and translates it into a strand of amino
acids. A molecule of tRNA has at one end a set of three bases that will complement the RNA strand; this
is called the anticodon. At the other end is a specific amino acid (see Figure 2.3). In this way, each set
of three nitrogenous bases on the mRNA strand codes for a specific amino acid. As each codon is read,
the tRNA brings in a new amino acid and the polypeptide chain grows.
http://www.uweb.ucsb.edu/~trevorc/techgt.html
Transcription
Translation
Cells use the two-step process of transcription and translation to read each gene and
produce the string of amino acids that makes up a protein. The basic rules for
translating a gene into a protein are laid out in the Universal Genetic Code.
RNA types
1. Ribosomal RNA (rRNA): make up ribosomes
2. Transfer RNA (tRNA): transport amino acids to ribosomes
3. Messenger RNA (mRNA): copied from DNA, conveys information from chromosomes to ribosomes
Transcription: production of mRNA copy of the DNA gene.
Gene: Section of DNA within a chromosome that codes for the synthesis of one protein. There are roughly 20-30,000 genes on the
23 pairs of human chromosomes.
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
Only 1 side of DNA in a gene gets transcribed:
http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/TT/TscriptD.html
A. Sense Strand: Strand of DNA in a gene which has the same nucleotide sequence as the m-RNA (except with T instead of U).
B. Antisense Strand: Name of strand of DNA that is transcribed to create m-RNA. It is the template used for making m-RNA.
RNA polymerase: enzyme that initiates transcription by binding to promoter (TAC code on DNA) at the 3' end of DNA
Promoter site: sequences in the DNA strand which accept RNA polymerase and initiate transcription
Elongation: mRNA bonds with DNA in small units, transcription bubble, adding bases Adenine to Uracil & Guanine to cytosine,
etc.. in the 5' to 3' direction (on the new m-RNA).
Termination: stop signal disengages RNA polymerase
]
Codon: sequence of 3 nucleotides on m-RNA that codes for one amino acid. Each amino acid has one to several different codons.
A Site with a good beginning Animation of Transcription (Needs Shockwave)
Much of DNA is non-coding base sequences, not genes
Intron: part of gene (DNA or mRNA) that does not code for polypeptide. It must be removed before translation.
Exon: coding part of DNA (or mRNA). The exon is translated during protein synthesis.
Translation: synthesis of protein by ribosomes
Anticodon: the 3 nucleotide sequence on t-RNA which the ribosome must fit against m-RNA to ensure that the correct amino acid is
placed in the growing protein during translation.
Initiation: Initiates translation. rRNA polymerase of ribosome binds to mRNA strand. 1st tRNA is bonded to mRNA.
Elongation: Ribosome reads mRNA chain in three nucleotide groups (codon) & inserts 2nd tRNA.
tRNA anti-codon (with amino acid) binds to mRNA codon
Ribosomes ...
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
are where translation occurs. Each ribosome is a complex of proteins and special RNA
called ribosomal RNA (rRNA). In both prokaryotes and eukaryotes, active ribosomes are
composed of two subunits called the large and small subunit. Bacterial ribosomes
(prokaryotic) are smaller than eukaryotic ribosomes.
Translocation: 5' to 3' sequence continues building amino acid polymers (protein), one codon at a time.
Termination: tRNA recognizes release factors of nonsense codon. Newly completed polypeptide is released from ribosome
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nucleic/chpt15/chpt15.htm

Sequence of nucleotides in DNA of a gene is transcribed into mRNA. Ribosomes
move along mRNA (5' to 3' direction) and read nucleotide sequence of mRNA one codon at a time.
A codon is translated into an amino acid by a tRNA with complementary sequence


basis for specificity between codon and amino acid lies in structure of tRNA.
structure of tRNA (Fig 3.21):
o
two dimensional shape like cloverleaf: 4 double-helical stems, plus 3 single stranded loops.
Biology 3rd Block Room 128
o
o
o
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
middle loop contains anticodon, which binds with a specific codon in mRNA by complementary base pairing.
3'-end of tRNA carries an amino acid. Each tRNA specific for a only one amino acid.
amino acids attached to 3'-end of tRNA (Fig 14.10)by enzymes called aminoacyl-tRNA synthetases. Each amino
acid has a specific synthetase (Fig 14.9). tRNAs with attached amino acid are said to be charged.
Ribosomes are protein factories

Each codon stands for a specific amino acid. There are
64 possible codons (triplet code) (Fig 14.5 ).
http://www.langara.bc.ca/biology/mario/Biol2430notes/biol2430chap14.html
http://www.langara.bc.ca/biology/mario/Assets/Geneticode.jpg
o Using mRNA to make proteins at the ribosomes
o mRNA , ribosomes,
1) mRNA tRNA
(page 187 in the book)
Biology 3rd Block Room 128
Mr. R. Bair Biology Teacher
Mrs. MV Smith Resource Teacher
When translation begins mRNA is bound to a complete ribosome so that the start codon is positioned
in the P site, ready for the first amino acid of the protein chain.
When both sites on the ribosomes are piled, a peptide bon can form and link the amino acids
After the peptide bond is formed, mRNA shirts on the ribosome so that a new codon is present in the
A site.
The sequence of amino acids in a gene determines the primary structure of a protein, it begins to fold
into a molecule with secondary and tertiary structures.
Stop codon UAA, UAG, AA do not code for amino acids but instead signal translation to stop.