Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

3.2Reproduction and Inheritance

Inheritance — Edexcel Linear - OL Revision Notes & Topical Questions

20 min read 29 parts Lesson 5 of 5 1 quiz

📚 Edexcel Linear - OL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
0%read
Lesson summary

The Genome, DNA, RNA and Protein Synthesis — EDEXCEL LINEAR - OL notes: Describe the structure of DNA and RNA and explain how a gene is transcribed and translated into a protein.The entirety of an organism's DNA is its genome.

  • chromosomes
  • double helix
  • complementary base pairing
  • uracil (U) replaces thymine
  • single-stranded
  • Transcription

Part 1 of 5Genome, genes and chromosomes

The entirety of an organism's DNA is its genome. A gene is a section of a DNA molecule that codes for a particular sequence of amino acids, and these sequences form proteins. Genes control our characteristics because proteins do important jobs in cells: structural proteins such as collagen in skin, enzymes and hormones.

In the nucleus the DNA double helix supercoils to form chromosomes, which are only visible during cell division.

1
Ordinary human body cells have 23 pairs of chromosomes (46 in total), the diploid number (2n).
2
One chromosome of each pair comes from each parent, and each pair is a homologous pair.
3
Genes sit at specific positions on chromosomes, which were mapped by the Human Genome Project.
4
The number of chromosomes differs between species: humans have 23 pairs, dogs 39 pairs and rice 12 pairs.

Part 2 of 5DNA structure

DNA (deoxyribonucleic acid) is the genetic material in the nucleus.

DNA structure
Double helix
It is a polymer of two strands coiled into a double helix.
Each strand has a sugar-phosphate backbone with bases attached: adenine (A), thymine (T), guanine (G) and cytosine (C).
Complementary base pairing
The strands are held together by complementary base pairing: A pairs with T and G pairs with C.
Because of this rule each strand can act as a template to build a new strand, which matters in cell division and in protein synthesis.
In exams, name the bases in full rather than relying only on the letters.

Part 3 of 5RNA structure

RNA (ribonucleic acid) is also a polynucleotide, a long chain of nucleotides.

RNA structure
Uracil (U) replaces thymine
It has adenine, guanine and cytosine, but uracil (U) replaces thymine.
Single-stranded
RNA is single-stranded, with alternating ribose sugars and phosphates and the bases projecting sideways.
Types: messenger RNA (mRNA), a copy of a gene that encodes a polypeptide; transfer RNA (tRNA),
  • which brings amino acids during protein synthesis; and ribosomal RNA (rRNA),
  • which forms part of ribosomes.
FeatureDNARNA
StrandsTwo (double helix)One
Base replacing TThymineUracil
SugarDeoxyriboseRibose

Part 4 of 5Transcription and translation

Turning a gene into a protein has two stages.

Transcription (in the nucleus):

1
Part of the DNA unwinds as hydrogen bonds between base pairs (A-T, G-C) break.
2
This exposes the template strand of the gene.
3
Free mRNA nucleotides in the nucleus pair with complementary bases on the template strand.
4
The nucleotides are joined to form a single strand of mRNA, a complementary copy of the gene.
5
The mRNA leaves the nucleus through a pore in the nuclear envelope.

Translation (in the cytoplasm, on ribosomes):

The mRNA attaches to a ribosome.
Anticodon
Free tRNA molecules each have an unpaired triplet called the anticodon at one end and a specific amino acid at the other.
Codon
The anticodon of a tRNA pairs with the complementary triplet (codon) on the mRNA, bringing its amino acid.
A second tRNA binds the next codon and a peptide bond forms between the neighbouring amino acids.
This continues until a stop codon is reached, which ends translation.
  • The finished chain is folded and modified into a protein such as an enzyme or antibody.

Alleles are alternative forms of the same gene; they differ slightly in base sequence, which is why they produce different versions of a characteristic.

Part 5 of 5Worked examples

  1. Name the base that pairs with adenine in DNA and the base that pairs with adenine in mRNA. [2]2 marks

  2. A DNA template strand reads TACGGT. Give the mRNA sequence made from it. [2]2 marks

  3. Describe the role of tRNA in translation. [3]3 marks

  4. State two differences between DNA and RNA. [2]2 marks

Key terms

TermMeaning
GenomeAll of an organism DNA.
GeneSection of DNA that codes for a protein.
Complementary base pairingA with T, and G with C, in DNA.
mRNAMessenger RNA; a copy of a gene carried from nucleus to ribosome.
TranscriptionMaking mRNA from a DNA gene in the nucleus.
TranslationBuilding a polypeptide at a ribosome using the mRNA code.
CodonTriplet of bases on mRNA coding for an amino acid.
AnticodonTriplet of unpaired bases on tRNA.

Avoid these mistakes

1
Writing thymine in mRNA — RNA contains uracil instead.
2
Saying translation happens in the nucleus — it happens on ribosomes in the cytoplasm.
3
Mixing up codon and anticodon — the codon is on mRNA; the anticodon is on tRNA.
4
Using only base letters — name adenine, thymine, guanine and cytosine in full.

Last updated:

\n