☰ Contents · Biology

The cell cycle. Mitosis and meiosis. Laboratory work

Lessons 11–12 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology, Grade 10, 1st edition. “Sharq” publishing and printing joint-stock company, Tashkent, 2017
12

Laboratory work 1

Textbook: pp. 58–59
GoalSolve problems on DNA, RNA, protein biosynthesis and energy metabolism using the rules.
New words
complementarity · komplementarlikcodon · kodonnucleotide · nukleotidproblem · masala
Explanation

The laboratory lesson consists of solving problems. Rules: 1) In DNA A = T and G = C, and A + G = T + C; there are 2 hydrogen bonds between A–T and 3 between G–C. 2) In double-stranded DNA the distance between neighbouring base pairs is about 0.34 nm; length = number of pairs · 0.34 nm. 3) mRNA is complementary to the DNA template strand (A–U, T–A, G–C); 3 nucleotides = 1 codon = 1 amino acid (not counting the stop codon). 4) Protein mass ≈ number of amino acids · 120 (average residue mass, a convention). 5) Energy: textbook conventional values – 38 ATP when 1 glucose is broken down aerobically and 2 ATP when anaerobically (lactic acid). Procedure: write the given data, decide which rule is needed, calculate, write the answer with its unit and draw a conclusion.

Worked examples
A DNA piece has 2400 nucleotides in total and 20% adenine. A = T = 20% · 2400 : 100 = 480 each; G = C = (100 – 40) : 2 = 30%, i.e. 720 each; length = 2400 : 2 · 0.34 = 408 nm.
mRNA: AUG UUU AAA GGU UGA. By the table (AUG – Met, UUU – Phe, AAA – Lys, GGU – Gly, UGA – stop) the protein is Met–Phe–Lys–Gly; the DNA template strand is TAC AAA TTT CCA ACT.
Class activity

“Problem contest”. Teams solve the same problem in different ways, compare answers and find each other’s mistakes.

Practice
1
A DNA piece has 2000 nucleotides and 24% thymine. How many guanine nucleotides are there? (Number only.)
2
One DNA strand segment is ACGTTAGCC. How many hydrogen bonds are there in total between this segment and its complementary strand? (Number only.)
3
How many nucleotides does the mRNA region have that codes a protein of mass 24000 (not counting the stop codon)? (Take the residue mass as 120; number only.)
4
Of 6 mol of glucose, 2 mol are broken down aerobically and 4 mol anaerobically (lactic). How many moles of ATP form in total? (Textbook values; number only.)