DRM Biology Y11 1 TRANSCRIPTION AND TRANSLATION From DNA to protein

A segment of DNA that codes for the synthesis of a protein is called a gene. The synthesis of protein in eukaryotic cells happens outside the nucleus in eukaryotic cells. But the DNA with the instructions to make a protein is inside the nucleus, so we need a “link”. RNA carries the information from the DNA in the nucleus to the ribosomes in the cytoplasm.

T R A N S C R I P T I O N Information in the DNA is copied into a new nucleic acid molecules called the messenger RNA. Only the section of DNA that codes for the selected gene is copied. Only one strand of the DNA is copied at one time. This strand is called the DNA template. TRANSCRIPTION takes place inside the nucleus in eukaryotes and in the cytoplasm in prokaryotes.

The RNA Polymerase unwinds and unzips DNA. The RNA Polymerase unwinds and unzips DNA. Next, the RNA Polymerase begins transcribing the template DNA at a specific point (promoter region). Next, the RNA Polymerase begins transcribing the template DNA at a specific point (promoter region). Complementary triphosphate nucleotides are added to template DNA strand from 5’ to 3’. Complementary triphosphate nucleotides are added to template DNA strand from 5’ to 3’. The RNA strand is identical to the non-coded DNA, but remember that T is replaced by U in the RNA. The RNA strand is identical to the non-coded DNA, but remember that T is replaced by U in the RNA.

DRM Biology Y115 The RNA polymerase adds NTPs, triphosphate nucleotides to form a new molecules of RNA. Two phosphate groups break providing energy for the reaction that adds the complementary nucleotide according to the sequence in the DNA template.

DRM Biology Y116 Transcription in bacteria, fungal cells, protists, animal cells and plant cells is the same, EXCEPT THAT in eukaryotes, the newly made mRNA must first be processed before leaving the nucleus. This is done to prevent damage to the mRNA from cytoplasmic enzymes and to remove junk info. Transcription in bacteria, fungal cells, protists, animal cells and plant cells is the same, EXCEPT THAT in eukaryotes, the newly made mRNA must first be processed before leaving the nucleus. This is done to prevent damage to the mRNA from cytoplasmic enzymes and to remove junk info. REMEMBER! the mRNA has the instructions from the DNA to make a protein. REMEMBER! the mRNA has the instructions from the DNA to make a protein.

T R A N S L A T I O N From mRNA to protein. From mRNA to protein. This takes place in the cytoplasm, in special structures called ribosomes. This takes place in the cytoplasm, in special structures called ribosomes. The instructions are read using the genetic code: a triplet of nucleotides codes for one amino acid. The instructions are read using the genetic code: a triplet of nucleotides codes for one amino acid.

3 RNAs are involved in translation mRNA: is the message to be read and interpreted. It has the instructions from the DNA. The mRNA has the message in triplets called CODONS. mRNA: is the message to be read and interpreted. It has the instructions from the DNA. The mRNA has the message in triplets called CODONS. rRNA: forms the ribosome, the platform on which amino acids a re joined to make a protein. rRNA: forms the ribosome, the platform on which amino acids a re joined to make a protein. tRNA: transfers a given amino acid from the cytoplasm to the ribosome, according to the sequence in the mRNA. The tRNA has the ANTICODONS complementary to the mRNA codons. tRNA: transfers a given amino acid from the cytoplasm to the ribosome, according to the sequence in the mRNA. The tRNA has the ANTICODONS complementary to the mRNA codons.

DRM Biology Y119

10 Comparing transcription and translation in prokaryotes and eukaryotes.

DRM Biology Y1111 The genetic code Universal Universal Redundant Redundant(degenerate)

DRM Biology Y1112 Translation in steps - I 1) First the small subunit of the ribosome binds to the mRNA. 2) Next, the large subunit now binds to create the peptidyl (or P) site and the aminoacyl (or A) site. The first tRNA, carrying the first amino acid, occupies the P site. This first tRNA has an anticodon complementary to the first codon in the mRNA. 3) The second tRNA enters the A-site as its anticodon is complementary to the second codon. Now there are 2 tRNA side by side, each with an amino acid. 4) Next, an enzyme joins both amino acids forming a peptide bond. 5) The first amino acid is transferred to the A-site, the first tRNA exits, the ribosome moves along the mRNA, and the next tRNA enters as it reads another codon.

DRM Biology Y1113 Translation in steps - II 6) As elongation continues, the growing peptide is continually transferred to the A- site tRNA, the ribosome moves along the mRNA, and new, complementary tRNAs enter. 7) When a stop codon is encountered in the A-site, a release factor enters the A-site and translation is terminated. When termination is reached, the ribosome dissociates, and the newly formed protein is released.

DRM Biology Y1114Summary

DRM Biology Y short animations transcriptiontranslation

DRM Biology Y1116 More animations to understand this mess! Y&feature=related (narrated) Y&feature=related (narrated) Y&feature=related Y&feature=related g&feature=related (with text) g&feature=related (with text) g&feature=related g&feature=related g&feature=related g&feature=related g&feature=related g&feature=related