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• Genes are coded DNA instructions that control
the production of proteins in the cell
Transcription
DNA
Translation
RNA
Proteins
A Molecular Definition of Genes
• Ribonucleic acid
• Like DNA
(deoxyribonucleic acid)
EXCEPT:
• 1) 5-carbon sugar is ribose
• 2) Single-stranded
• 3) Contains URACIL (U)
instead of thymine (T)
What is RNA?
• Messenger RNA (mRNA)
• Serves as “messengers” from DNA to the rest of the
cell
• Ribosomal RNA (rRNA)
• Makes up ribosomes, along with protein
• Transfer RNA (tRNA)
• Transfer amino acids to the ribosome
Types of RNA
• TRANSCRIPTION is the copying of a sequence of
DNA into a complementary sequence of mRNA
• Requires enzyme, RNA polymerase
• Binds to and separates DNA strands
• Uses strand of DNA as template to assemble
mRNA
• RNA polymerase binds to promoters, sequences of
DNA that signal where to begin transcription
Transcription
• How would we transcribe this sequence of DNA into
mRNA?
DNA sequence:
mRNA sequence:
GTAAGCTC
CAUUCGAG
• DNA of eukaryotic genes contains sequences
called introns, which are NOT involved in
coding for proteins
• Exons are sequences that code for proteins
RNA Editing
• Amino acid = smallest
part of a polypeptide
• Polypeptide = a chain
of amino acids.
• Protein = a complex
structure made of
polypeptides
Things Found in a Cell
• The genetic code is responsible for building all the
proteins in the body using 20 different amino acids.
• mRNA is the genetic code
• 4 RNA bases: U, A, G, C
• Each coded “message” is 3 bases long
• How many 3 letter words can you make from the
letters A,T,G and C?
• 4 x 4 x 4 = 64
The Genetic Code
• Codons are three letter “words” that specify an amino acid
• There are 64 possible codons
Example mRNA sequence:
UCGCACGGU
We would read this as:
UCG – CAC – GGU
Corresponding amino acids:
Serine – Histidine – Glycine
Some amino acids are specified by more than one codon, and
some codons are “START” and “STOP” signals
Codons
2 different types of amino acid charts…
• Which amino acid does
AUG stand for?
• MET = methionine
• Which amino acid
does CUC stand
for?
• LEU = leucine
Which amino acid
does UGA Stand for?
• UGA = Stop
• TRANSLATION is the
process of decoding the
information from mRNA to
produce proteins
• mRNA = instructions
• Ribosomes join the
amino acids together as
directed by the tRNA
• Starts with codon-AUG
• Ends with a stop codon
Translation
• mRNA that has
been
transcribed
from DNA in
the nucleus is
released to the
cytoplasm
• mRNA attaches to the
ribosome
• As codons move
through the ribosomes,
tRNA transfers the
correct amino acid to
the growing
polypeptide chain
• Transfers the correct amino acid
to the chain
• At one end an amino acid is
attached
• At the other end there is an
anticodon that pairs with the
mRNA
• Occurs at the ribosome
tRNA
• Anticodons are complementary to the mRNA
sequence
• Which anticodon would be on the tRNA that
would pair with UCG on the mRNA?
• AGC
• Ribosome forms a
bond between the
amino acids and
releases the used tRNA
• Protein grows until the
STOP codon is reached
• Ribosome then releases
the protein and the
mRNA
• Genes contain instructions for making proteins
• Many proteins are enzymes that catalyze and regulate
chemical reactions
• These proteins can determine an organism’s traits
• For example:
• Enzymes can determine pigment color of a flower or
human blood type
Genes &
Proteins
• Put your answers at the bottom of
your notes (they will be returned
to you after they are graded)
• Open textbook to pg. 303
Quiz Time
1. Which nitrogenous base replaces thymine (T) in
RNA?
2. How many strands are in RNA?
3. How many letters or bases, make up a codon?
4. What gets made during Translation?
5. Which amino acid gets made from the codons
U-U-C? Use pg 303 in book.
QUIZ