Transcription and Translation
S. HS. 3.2.1
DNA
• DNA (DeoxyriboNucleic Acid) is the information
for life; it is made of repeating nucleotides and
appears as a twisted ladder shape (double
helix). Watson and Crick are responsible for
developing a model of this structure.
– Nuleotides of DNA consist of:
1.)deoxyribose-5 carbon sugar
2.)phosphate
3.)1 nitrogen base-adenine, guanine, cytosine, or thymine
DNA
• The nitrogen bases form the steps on the ladder
or rungs of the ladder; they do this by pairing
with their compliment
– A pairs with T
– C pairs with G
●A nucleotide is named according to the base it
contains
♦phosphate and sugar form the backbone(sides) of ladder
♦nitrogen bases stick out like teeth on a zipper
(picture)
DNA
• Before a cell can divide, DNA must make a
copy of itself (DNA Replication)
• Without this process, new cells only have
half the DNA of their parents
• With this, the genetic makeup of an
organism can be passed to new cells
during mitosis or to new generations
through meiosis followed by sexual
reproduction.
DNA to Protein
• The sequence of nucleotides in an organism is the
genetic code of an organism and can be converted to a
sequence of amino acids in proteins.
• RNA like DNA is a nucleic acid, like DNA. It too is made
up of nucleotides
►3 major differences:
1.)RNA is single stranded-DNA is double
2.)RNA has ribose-DNA has deoxyribose
3.)RNA has uracil-DNA has thymine
(picture)
Transcription
• DNA
→
mRNA
(in nucleus) (leaves nucleus, goes to ribosome)
◊Transcription (rewriting the code) takes place in
the cell’s nucleus where enzymes make an
RNA copy of a DNA strand; mRNA is made.
◊This process is similar to DNA replication
except that the result is one single stranded
RNA molecule.
Transcription
◊ DNA unzips first, then free floating RNA
nucleotides pair with their complimentary
DNA nucleotides on one DNA strand
◊ When pairing is complete, mRNA breaks
away and leaves the nucleus
Translation
• mRNA
→
protein
(nucleotides)
(amino acids)
■ Translation is the process of converting the info in
mRNA into an amino acid sequence
■ Translation takes place at the ribosomes in the
cytoplasm.
■ All organisms use the same amino acids, making the
genetic code universal.
Transcription and Translation
•
If one DNA strand has the base sequence G C T A A T G C A, the other
strand is
_ _ _ _ _ _ _ _ _ (its compliment)
• Once you have found the compliment, the mRNA strand must be completed.
• After the mRNA is complete, the codons can be underlined.
• The codons can then code for an amino acid.
For instance, using the above strand, the process would appear as this:
DNA
G C TAAT G C A
CS
C GATTAC GT
mRNA C G A U U A C G U
A.A.
Arg
Leu
Arg
Mutations
•
Mutations are changes in DNA; these are natural processes that produce
genetic diversity in organisms
•
There are different types of mutations
– Point or Substitution Mutation= a single nucleotide is replaced by another of the
three nucleotides
DNA
TAG G CA
(m)DNA T A C G C A *Notice two amino acids will still be coded
– Frameshift Mutation= a single nucleotide is inserted or deleted into the DNA
strand; when this occurs, the reading of the amino acids will shift to the right or
left respectively by one base
DNA
T A G G C A - Italicized G is deleted
(m)DNA T A G C A *Notice only one amino acid will be coded
DNA
T A G G C A – An adenine nucleotide is added
(mDNA) T A G G A C A – *Notice that still only two amino acids can be formed
because a codon must include three nucleotides in order to form an amino acid
Transcription and Translation
Questions
1.) A base sequence is shown below.
ACAGTGC
How would the base sequence be coded on
mRNA?
A TGTCACG
B GUGACAU
C UGUCACG
D CACUGUA
Transcription and Translation
Questions
2.) A scientist puts nucleotide chains of UUUUUU in a test
tube under conditions allowing protein synthesis. Soon
the test tube is full of polypeptide chains composed of
only the amino acid phenylalanine. What does this
experiment indicate?
A The amino acid phenylalanine is composed of uracil.
B UUU codes for the amino acid phenylalanine.
C Protein synthesis malfunctions in test tubes.
D Most proteins contain only one type of amino acid.
Transcription and Translation
Questions
3.) 5’ ATCAGCGCTGGC 3’
The above sequence of DNA is part of a
gene. How many amino acids are coded
for by this segment?
A 4
B 8
C 12
D 20
Transcription and Translation
Questions
4.) A strand of mRNA
containing the repeating
sequence
AAGAAGAAGAAG could
code for which of the
following amino acid
sequences?
A lys-arg-glu-lys
B ser-ser-glu-glu
C lys-arg-lys-arg
D lys-lys-lys-lys
Transcription and Translation
Questions
5.) Although there are a limited number of amino
acids, many different types of proteins exist
because the
A size of a given amino acid can vary.
B chemical composition of a given amino acid
can vary.
C sequence and number of amino acids is
different.
D same amino acid can have many different
properties.
Transcription and Translation
Questions
6.) 5’ G T A _ _ _ A A 3’
3’ C A T G C A T T 5’
This segment of DNA has undergone a
mutation in which three nucleotides
have been deleted. A repair enzyme
would replace them with
A CGT.
B GCA.
C CTG.
D GTA.
Mutations
7.) Which of these would most likely cause a
mutation?
A the replacement of ribosomes on the
endoplasmic reticulum
B the insertion of a nucleotide into DNA
C the movement of transfer RNA out of
the nucleus
D the release of messenger RNA from
DNA
Mutations
8.) Mutations within a DNA sequence are
A unnatural processes that are harmful to
genetic diversity
B unnatural processes that always affect
the phenotype
C natural processes that always affect the
phenotype
D natural processes that produce genetic
diversity
Genetic Engineering Questions
9.) The bacterium Agrobacterium tumefaciens
infects plants, and a portion of its DNA is
inserted into the plant’s chromosomes. This
causes the plant to produce gall cells, which
manufacture amino acids that the bacterium
uses as food. This process is a natural example
of
A hybridization.
B grafting.
C genetic manipulation.
D polyploidy
Genetic Engineering Questions
10.) Genetic engineering has produced goats
whose milk contains proteins that can be used
as medicines. This effect was produced by
A injecting foreign genes into the goats; udders.
B mixing foreign genes into the milk.
C inserting foreign genes into fertilized goat
eggs.
D genetically modifying the nutritional needs of
the goat’s offspring.
Slide Answers
1)
2)
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C
B
A
D
C
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A
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C
C