AS Human Biology Unit 11

Text questions

P190/Q1

DNA:	ATC GAC CCT AGA
DNA probe:	TAG CTG GGA TCT

P191/Q2

Reverse transcriptase = enzyme which controls the synthesis of complementary DNA (cDNA) from mRNA.

Restriction endonuclease/restriction enzyme: enzymes which "cut" DNA by hydrolysing phosphodiester bonds and breaking H - bonds at specific base sequences within their molecules. (N.B. these enzymes are made naturally by bacteria. Bacteria use them to destroy DNA of bacteriophages/bacterial viruses, which sometimes infect them).

P192/Q3

Restriction endonucleases are specific. They will cut a DNA chain into fragments by breaking H and phosphodiester bridges between specific nucleotides. The broken bonds of the DNA chain are parts of "sticky ends". The cut fragments of DNA ("foreign gene") will be then inserted into DNA of a vector (plasmid). There is a gap in the DNA of the vector, which has been cut open with the same restriction enzyme. When the "foreign gene" is inserted into the gap, reformation of H and phosphodiester bridges will follow. The process is controlled by DNA ligase, an enzyme which joins the sticky ends. The broken bonds can only be reformed, if both the parts of DNA (i.e. the one of a foreign gene and that of a plasmid) are complementary with respect to A-T, C-G rule of bonding.

P192/Q4

The ampr gene is an example of a genetic marker. Using antibiotic resistance as a genetic marker involves splicing two genes into plasmids: one for the human protein we want to make and a second for antibiotic resistance. If a bacterial cell has successfully taken up the plasmid with the human gene, it will also be resistant to the antibiotic. Cells that have not taken up the plasmid will be susceptible to the antibiotic. When bacteria are grown on agar plates contaminated with antibiotic, only those bacteria with a gene for resistance will form colonies.

P194/Q5

Transgenic cows = cows whose cells contain DNA from another species (e.g. human). The human fragments of DNA present in the cow's DNA contain genes coding for proteins, such as haemoglobin. Haemoglobin will be produced by the cow's mammary glands and will be present in their milk.

P196/Q6

Cystic fibrosis is an inherited disorder caused by a defective gene, which codes for abnormal/faulty CFTR protein. Eugenics could be used to insert a normal allele of the gene into humans (via eggs/sperm before fertilisation), so that normal CFTR proteins are synthesised.

Assignment

P199/Q1

a)
b)

Features of muscle adhesive protein	Why are these features important
Made of 10 amino-acids 3� structure changes Sets into a solid	3� structure can change easily Protein can squeeze into small cracks Improved adhesion
Features of enzyme protein	Why are these features important
Made of more than 10 a/a Fixed 3� structure Colloidal state in the cytoplasm	3� structure is stable/fixed Fixed shape of the active site Chemical reactions take place in aqueous solutions

P200/Q2

Antibodies will cause agglutination of the protein and, consequently, its removal from the body.

Replacement of blood plasma proteins (lost via urine as a result of kidney failure/illness);
Treatment of various forms of extensive and prolonged swelling of the body tissues (presence of plasma proteins lowers WP of the blood, hence increases re-absorption of the tissue fluid back to the blood vessels).

P200/Q3

10 a/a in the sequence x 3 nucleotides = 30 nucleotides;

5 different a/a = 5 different sorts of tRNA

(i) From a/a work out sorts of tRNA; from tRNA work out mRNA coding for the a/a sequence;

(ii) Because the code may be degenerate (more than 1 triplet/codon of mRNA codes for one a/a).

P200/Q4

As a result of post-translational modification inactive form of mussel adhesive protein is converted to its active form. As a result it gains its properties: no distinct 3� structure. The process takes place after translation, hence its name.

(i) DNA, mRNA, tRNA, ribosomes present;

(ii) No Golgi body (needed for post- translational modification);

DNA, mRNA, tRNA, RER, and Golgi body present (for modification);

P200/Q5

GM food plants producing mussel adhesive protein would pose a risk to animals/humans (: cross pollination with non-GM varieties or possibility of GM plants reaching the open market);

Close wild relatives in the area: cross- pollination possible (→ GM plant will not produce mussel adhesive protein (m.a.p.) or the genes coding for m.a.p. will enter the gene pool of the wild relatives).

Examinations

P201/Q1	a)	Restriction endonucleases are specific. They will cut fragments of DNA by breaking H and phosphodiester bridges between specific nucleotides. The broken bonds of the DNA chain are parts of "sticky ends". The cut fragments of DNA ("foreign gene") will be then inserted into DNA of a vector (plasmid). There is a gap in the DNA of the vector, which has been cut open with the same restriction enzyme. When the "foreign gene" is inserted into the gap, reformation of H and phosphodiester bridges will follow. The process is controlled by DNA ligase, an enzyme, which joins the sticky ends. The broken bonds can only be reformed, if both the parts of DNA (i.e. the one of a foreign gene and that of a plasmid) are complementary with respect to A-T, C-G rule of bonding.
	b)	DNA ligase
	c)	Using antibiotic resistance as a genetic marker involves splicing two genes into plasmids: one for the human protein we want to make and a second for antibiotic resistance. If a bacterial cell has successfully taken up the plasmid with the human gene, it will also be resistant to the antibiotic. Cells that have not taken up the plasmid will be susceptible to the antibiotic. When bacteria are grown on agar plates contaminated with antibiotic, only those bacteria with a gene for resistance will form colonies.
P201/Q2	a)	Gene 1 cut from chromosome of sunflower seeds using restriction enzyme; DNA of a vector cut open with the same restriction enzyme; Gene spliced into the vector using DNA ligase;
	b)	Gene 2: codes for an enzyme that controls synthesis of the S-rich protein (according to the code of gene 1). As a result, clover leaves have a high proportion of S-rich proteins. Gene 3: S-rich protein should be digested in the abomasum. In this way most of S-rich a/a will be available for absorption by the blood of the sheep. If digested by the bacterial flora of the rumen, then less of S-rich a/a would be available for absorption into the bloodstream of the sheep.