Protein Synthesis
5.1 I can explain the steps in the process of transcription, along with
where they take place (this includes the role of DNA and mRNA)
5.2 I can explain the steps in the process of translation, along with where
they take place (this includes the role of mRNA, tRNA, ribosomes (rRNA),
and amino acids)
5.3 I can list the three different types of RNA and describe the function of
each.
5.4 I can describe at least three differences between DNA and RNA.
5.5 I can label the following items in pictures of transcription and
translation:
DNA sense strand, DNA nonsense strand, RNA polymerase, mRNA
strand, ribosome, start codon, stop codon, amino acid,
polypeptide chain (protein), tRNA, anti-codon, peptide bond
5.6 I can describe at least three different types of mutations in DNA, and
their possible effects on the organism.
I can explain the steps in the process of
transcription, along with where they take place
(this includes the role of DNA and mRNA)
Every cell faces a
fundamental problem
when making proteins.
 The instructions for
making the proteins
are in the nucleus on
the DNA.
BUT…
 The location for
making proteins is
outside the nucleus at
the ribosomes.
 The
first part of the
solution is a
process called…
…TRANSCRIPTION
 First, an
enzyme called RNA polymerase
attaches to DNA at the beginning of a gene.
 The enzyme “unzips” the double helix strand
and begins to “read” the instructions, coded in
the sequence of the letters A, T, C, and G.
 As
the enzyme reads the DNA code, it copies it
by attaching complementary RNA nucleotides.
 The result is a strand of mRNA (messenger
RNA) which carries the instructions for making
a protein.
RNA polymerase
Growing
mRNA strand
RNA nucleotide
 Well, we’re
making a copy of the DNA,
and the DNA can be found where?
• In the nucleus.
 The
DNA can’t leave the nucleus for two
reasons:
• It’s too large to get through the pores, and it’s too
precious to send it out into the cytoplasm where
digestive enzymes could break off pieces of it.
 …it
leaves the nucleus to go take the
DNA’s message to a ribosome where the
protein will be made.
 So
mRNA solves the problem of getting
the information from the nucleus to the
cytoplasm.
 Now
to make the protein!!
I can explain the steps in the process of translation,
along with where they take place (this includes
the role of mRNA, tRNA, ribosomes (rRNA), and
amino acids)
 The
cell has another problem. It has to
take the “language” of nucleic acids
(DNA/RNA) and turn it into the language
of amino acids (protein).
 So it needs a translator…
…otherwise known as the ribosome!
 First, the
mRNA threads into the
ribosome, until the “start codon” – AUG,
reaches the P site in the ribosome.
 Next, the
ribosome brings in a tRNA (transfer
RNA).
 On one end of the tRNA is an anti-codon that is
complementary to the codon on the mRNA.
 On the other end of the tRNA is an amino acid.
A
tRNA also binds at the A site. A peptide bond
forms between the two amino acids, connecting
them together.
 Then the tRNA in the P site leaves (leaving
behind its amino acid), and the ribosome
moves to the next codon. The process continues
this way until it reaches a stop codon.
 Once
the ribosome reaches a stop codon,
everything detaches.
 The protein finishes its production by folding a
certain way so that it can do its job.
 The ribosome will make another protein.
 The mRNA gets recycled by digestive enzymes in
the cytoplasm.
 The tRNA will pick up more of their amino acids
to help build another protein.
I can list the three different types of RNA
and describe the function of each.
1.
2.
3.
mRNA (messenger RNA) – carries the
message of the DNA from the nucleus to
the ribosome; created during
transcription.
tRNA (transfer RNA) – transfers amino
acids to the growing chain of amino acids
in the ribosome during translation.
rRNA (ribosomal RNA) – what ribosomes
are made of.
I can describe at least three differences
between DNA and RNA.
DNA:
RNA:
• Double-stranded
• Single-stranded
• Deoxyribose is the sugar
• Ribose is the sugar
• G, C, A, and T are the
bases
• G, C, A, and U are the
bases
• Very long
• Much smaller (one gene)
I can label the following items in pictures of
transcription and translation:
DNA sense strand, DNA nonsense strand, RNA
polymerase, mRNA strand, ribosome, start
codon, stop codon, amino acid, polypeptide
chain (protein), tRNA, anti-codon, peptide
bond
DNA nonsense
strand
DNA sense
strand
mRNA strand
RNA
polymerase
Peptide
bond
tRNA
Polypeptide
chain
Amino acid
ribosome
anticodon
Start
codon
Stop codon
mRNA
strand
I can describe at least three different
types of mutations in DNA, and their
possible effects on the organism.
 There
are two main categories of
mutations that we discuss:
 Chromosomal mutations, which involve
changes in whole genes on a
chromosome (we will look at these next
unit)
 Gene mutations, which involve changes
in parts of genes.
 There
are two main types of gene
mutations: point mutations, and
frameshift mutations.
 A point mutation is when one base is
switched out for another base. It only
affects that one amino acid in the
sequence.
 A frameshift mutation is when one base
is deleted or added, which shifts all the
bases after it, affecting all of the amino
acids in the sequence after the mutation.
 Let’s
say the following sentence is a gene,
and each word in the sentence is a codon
(even though the words have more than
three letters):
Biology students are really nice
people.
 For
a point mutation, one base is
switched for another base.
Biology students ate really nice people.
 We
changed the “r” in are to a “t.”
 As you can see, only one word was
affected.
 However, the whole meaning of the
sentence has changed.
 Look
at your codon chart. Is every amino
acid coded for by one codon?
 No! There are repeats, right?
 So if we changed the last base of the codon,
sometimes it would still code for the same
amino acid.
 If this is the case, is there any change in the
protein?
 No – we call it a silent mutation because
there was no effect on the organism.
 In
an addition mutation, one base is
repeated. So we will add one letter twice.
Biology students sar enic epeopl e.
 We
put in an additional “s” after
students.
 Now, every word (or codon) after the
addition is affected because every base
afterward is shifted down one.
 In
a deletion mutation, one base is
deleted from the sequence.
Biology studenta ren icep eople.
 We
deleted the “s” at the end of students.
 Now, it shifts all the bases afterward up
one.
 Effects
of mutations can be minor, or
severe. They can be beneficial, harmful,
or as we’ve seen, neutral.
 It’s hard to discuss which type is “worse”
than others, because while frameshifts
render the entire protein useless and
may appear worse at a glance, point
mutations can be equally devastating.
 Let’s take a look at one such case.