Question

4. This is a coding DNA : 5’ ATG AGT GAT CTA GAC AGA CTT GCA AGC CGG …3’

(a) Predict the complementary strand and identify the strand name of it. (3' --> 5’)

(b) Predict the mRNA sequence (5' --> 3’) for the given coding strand.

(c) Predict the amino acid sequence of the gene.

(d) Predict the amino sequence, if there is a base substitution from A to T at the 16^th base.

(e) Which type of mutation and protein will result from the base substitution?

(f) Identify the location(s) likely to be cut by the restriction endonuclease XbaI, whose recognition site is 5’…T^CTAGA…3’, and predict the digested DNA sequence (double stranded).

Answer 1

coding DNA: 5’ ATG AGT GAT CTA GAC AGA CTT GCA AGC CGG …3’

A)                 3’ TAC TCA CTA GAT CTG TCT GAA CGT TCG GCC---5’ it is the template strand

B) mRNA is similar to the coding strand except that T is replaced by U

5’ AUG AGU GAU CUA GAC AGA CUU GCA AGC CGG …3’

C)              Met   Ser   Asp   Leu   Asp Arg   Leu   Ala Ser     Arg

D)    if there is a base substitution from A to T at the 16th base.

5’ ATG AGT GAT CTA GAC TGA CTT GCA AGC CGG …3’  substitution

mRNA    5’ ATG AGT GAT CTA GAC UGA CTT GCA AGC CGG …3’

AA seq       Met Ser   Asp Leu   Asp stop

E) Generally, a base substitution causes a change in one codon of the protein and these are called point mutations In the above example a base substitution created a stop codon which prematurely ends the synthesis of the polypeptide chain. So it produces premature protein chain

F)           5’ ATG AGT GAT CTA GAC AGA CTT GCA AGC CGG …3’

              3’ TAC TCA CTA GAT CTG TCT GAA CGT TCG GCC---5’

If the restriction endonuclease XbaI, recognition site is 5’…T^CTAGA…3’, the sequence of digested DNA is

5’ ATG AGT GAT                        

3’ TAC TCA CTA GAT CTG TC +

CTA GAC AGA CTT GCA AGC CGG …3’

T GAA CGT TCG GCC---5’     (with sticky ends)