chapter 10.1
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From Genes to Proteins
Grade 10 BiologySpring 2011
Complete this table as we take a journey learning about RNA:Property DNA RNA
Bases
Backbone
Number of strands
Base Pairing
Full name
Sugar
Function
Compare the structure of RNA with that of DNA
Summarize the process of transcription Relate the role of codons to the
sequence of amino acids that results after translation
Outline the major steps of translation Discuss the evolutionary significance of
the genetic code
http://www.youtube.com/watch?v=983lhh20rGY
Traits are determined by proteins that are built according to instructions coded in DNAEx. Eye colour
Proteins are not built directly from DNARibonucleic acid is involved (RNA)
RNA: nucleic acid, molecule made of nucleotides linked together
RNA differs from DNA in 3 ways:1. Single strand of nucleotides2. Contain 5-Carbon sugar Ribose3. Has bases A, G, C and U
URACIL A = U; G = C
Transcription: process where instructions for making a protein are transferred from a gene (DNA) to an RNA molecule
Translation: cells use two different types of RNA (rRNA and tRNA) to read the instructions made on mRNA and put together the amino acid that makes up the protein
Gene expression: entire process by which proteins are made based on information encoded in DNAAka: protein synthesis
RNA polymerase: enzyme that adds and links complementary RNA nucleotides during transcription
Steps of TRANSCRIPTION:1. RNA polymerase binds to the genes
promoter Promoter: specific sequence of DNA that acts
as a “start” signal for transcription
Steps of TRANSCRIPTION:2. RNA polymerase then unwinds and
separates the two strands of the double helix, exposing the DNA nucleotides on each strand
Steps of TRANSCRIPTION:3. RNA polymerase adds and then links
complementary RNA nucleotides as it “reads” the gene. RNA moves along the nucleotides of the DNA strand that has the gene (only one of the strands). Follows base pairing rules. A = U, G = C
RNA polymerase eventually reaches “stop” signal in DNA
“Stop” is sequence of bases that marks the end of the gene
RNA nucleotides linked by covalent bonds
Behind RNA, DNA strands close (zip) back up
Transcription uses DNA nucleotides as a template
Only part of one strand (the gene) of DNA serves as the template
Prokaryotes:Transcription occurs in cytoplasm…why?
No nucleus
Eukaryotes:Transcription occurs in nucleus
During transcription many copies of RNA are made simultaneously from a single gene
http://www.youtube.com/watch?v=ztPkv7wc3yU
http://www.youtube.com/watch?v=5bLEDd-PSTQ
Messenger RNA (mRNA) is made when a cell needs a particular protein
mRNA: form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation
Translation: information translated from the language of RNA (nucleotides) to the language of proteins (amino acids)
Codons: RNA instructions are written as a series of 3-nucleotide sequences on the mRNA
Each codon along mRNA strand corresponds to an amino acid or signifies a start or stop signal for translation
Genetic Code: the amino acids and start and stop signals that are coded for by each of the possible 64 mRNA codons
1. Find the first base of the mRNA codon along the left side of the table
2. Follow that row to the right until you are beneath the second base of the codon
3. Move up or down in that section until you are even, on the right side of the chart, with the third base of the codon
Translate this mRNA sequence into amino acids:
Translation takes place in the cytoplasm Transfer RNA (tRNA): single strands
of RNA that temporarly carry a specific amino acid on one end Each has an Anticodon: a three nucleotide
sequence on a tRNA that is complementary to an mRNA codon
Transfer this mRNA sequence into its tRNA anticodon and its amino acid
tRNA anticodons: •CAA•UGG•CUA•GUC
Ribosomes: composed of both proteins and ribosomal RNA Each ribosome temporarily holds one mRNA
and two tRNA molecules rRNA: RNA molecules that are part of
the structure of ribosomes
Lets make a small poster that summarizes the 7 steps of translation!
Step 1:Translation begins when mRNA leaves
nucleus and enters cytoplasm mRNA, two ribosomal subunits, and tRNA
carrying the amino acid methionine form a functional ribosome
mRNA “start” codon AUG, signals beginning of protein chain, is oriented in ribosome in the P site
tRNA molecule carrying methione can bind to the start codon
Step 2:Codon in the area of the ribosome called
the A site is ready to receive the next tRNA tRNA with complementary anticodon arrives
and binds to the codon in the A site tRNA is carrying its specific amino acid
Step 3:Both A and P site have tRNA molecules,
each carrying an amino acidEnzymes help form a peptide bond between
adjacent amino acids
Step #4: tRNA in P site detachesLeaves behind its amino acid, and moves
away from the ribosome
Step #5: tRNA (with its protein chain) in A site,
moves to P site Because anticodon remains attached to
codon, tRNA molecule and mRNA molecule move as a unit
Result: new codon is present in A site, ready to receive the next tRNA molecule and its amino acid
Amino acid is carried to A site by a tRNA and then bonded by a peptide bond to the growing protein chain
Step #6: tRNA in the P site detaches and leaves its
amino acid
Step #7:Steps 2 through 6 are repeated until a stop
codon is reachedStop codon is one of three codons
UAG, UAA, UGA No tRNA molecule with a complementary
anticodon Because there is no tRNA molecule to fit
into the empty A site, protein synthesis stops
Newly made protein is released into the cell
Many copies of the same protein are made from a single mRNA molecule
Once ribosome has moved past the start signal another ribosome can come in and start translating
Genetic code is nearly universal With few exceptions the genetic code is
the same in all organisms Evidence for common ancestor
The gene is part of the DNA, The gene is TRANSCRIBED by the mRNA, The mRNA goes to the ribosome, rRNA is part of the ribosome, TRANSLATION occurs on the ribosome, tRNA has an anticodon, The anticodon matches to the mRNA codon, The tRNA brings in the amino acid, First to the P then the A site, The amino acids are connected by a peptide
bond, And that’s how we make a protein!
Lets watch a video of transcription and translation for review!
http://www.youtube.com/watch?v=bpMhgAGybe4&feature=related
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