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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
mRNA
– 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
tRNA
Types of RNA
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
tRNA
Bring
amino acids to
ribosome
Transcription: DNA
RNA
• Occurs in NUCLEUS
• mRNA produced by copying part of 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
• RNA polymerase binds to specific regions of DNA in
order to start making mRNA
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Transcription
The Genetic Code & Intro to
Translation
• 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
What is the DNA sequence that coded
for this mRNA sequence?
AGCGTGCCA
Read 3 bases at a time –
UCG – CAC – GGU
Codons represent different amino acids
UCG – CAC – GGU
Serine – Histadine – Glycine
The Genetic Code
mRNA Sequence:
UCG
CAC
GGU
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
mRNA Sequence:
UCG
CAC
GGU