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