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RNA & Protein Synthesis
RNA and Protein Synthesis
• Genes are coded DNA instructions that control the production of proteins within the cell
• DNA codes for PROTEINS• Must copy part of the nucleotide sequence from
DNA into RNA (ribonucleic acid) which then helps make proteins– Proteins are made in ribosomes – need RNA to go to
ribosomes as the DNA cannot leave the nucleus
Structure of RNA
• Long chain of nucleotides– A 5-carbon sugar (ribose)– A phosphate group– And nitrogenous bases
• Differences between RNA and DNA:– Ribose (RNA) vs. deoxyribose (DNA)– RNA is single-stranded, DNA is double-stranded– RNA has Uracil (U) in place of Thymine (T)– In RNA, A bonds with U, and C bonds with G
• RNA is a disposable copy of DNA – it is a working copy of a single gene
RNA Base-Pairing Rule
A = U
G = C
Types of RNA
• Protein synthesis – assembly of amino acids into proteins controlled by RNA
• Three types of RNA– Messenger RNA (mRNA) – carry copies
of instructions for making amino acids– Ribosomal RNA (rRNA) – proteins
assembled on ribosomes– Transfer RNA (tRNA) – transfers each
amino acid to ribosome
mRNAtRNA
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RNA
Messenger RNA Ribosomal RNA Transfer RNA
mRNA Carry instructions rRNACombine
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DNA Ribosome Ribosomes
Types of RNA
Transcription: DNA RNA
• Occurs in NUCLEUS• Transcription is taking DNA and making mRNA• mRNA produced by re-writing the nucleotide sequence
of DNA into a complementary sequence in mRNA = transcription
• During transcription, RNA polymerase (similar to DNA polymerase) binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA
RNADNA
RNApolymerase
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
Transcription
Transcription
Translation & The Genetic Code:mRNA Proteins
• Occurs in RIBOSOMES• Translation is taking mRNA and making proteins• Proteins code for traits!• Proteins are made by joining amino acids into long
chains called polypeptides• There are 20 different amino acids – the order of amino
acids determine what proteins will be made• “Language” of mRNA instructions is the genetic code –
codes for proteins• RNA contains four bases A, U, C, and G – where A and
U can bond together and C and G can bond together
The Genetic Code (continued)
Genetic code is read THREE letters at a time, so that each “word” of coded message is 3 bases long. Each 3 letter “word” in mRNA is called a codon which identifies a single amino acid used in a protein
Example: mRNA sequence – UCGCACGGU
Read 3 bases at a time –
UCG – CAC – GGU
Codons represent different amino acids UCG – CAC – GGU
Serine – Histadine – Glycine
What is the DNA sequence that coded for this mRNA sequence?
AGCGTGCCA
The Genetic Code (continued)
• Some amino acids can be specified by more than one codon (because there are only 20 amino acids, and 64 possible codons, some codons will overlap)
• 3 “stop” codons – signal the end of a protein• Codon AUG specifies methionine – a “start”
codon for the beginning of the protein• A chart is used to decode the codons into their
respective amino acids
The Genetic CodemRNA Sequence:
UCG
CAC
GGU
mRNA Sequence:
UCG
CAC
GGU