MGSLG. (2020). Module 1 Unit 2 study material

1) DNA and where it is found

In the nucleus of almost every cell in your body is the collection of DNA needed to make you. DNA in the nucleus is grouped into 23 sets of chromosomes that are called your genome. DNA is grouped into groups called genes within each chromosome. Your genome contains about 35000 genes.. Some interesting facts regarding chromosomes: 

  • Chromosome 1 is the largest chromosome with roughly 250 million nucleotide base pairs, and 4316 genes have been identified on this chromosome.  If we could stretch out this chromosome it would be 8.5 cm. 890 diseases are linked to this chromosome (Alzheimer's type 4, breast cancer etc.)
  • Chromosome 21 is the smallest with roughly 48 million nucleotide base pairs, with between 477-635 genes.  Diseases related to genes on chromosome 21 are Alzheimer, lateral sclerosis, Down syndrome, certain types of deafness and 8 other identified syndromes.

Following is a diagram illustrating where DNA is found in a cell:



The Structure of DNA 

Each nucleic acid consists of a number of basic building blocks called nucleotides. Each nucleotide consists of three parts:

  • 1 phosphate ion
  • 1 pentose sugar
  • 1 nitrogenous base.

 The structure of a nucleotide:


  • The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rings”.
  • There are four types of nitrogenous bases:
    • Thymine
    • Guanine
    • Cytosine
    • Adenine


  • A gene is a section of DNA that codes for a protein
  • Each unique gene has a unique sequence of bases
  • This unique sequence of bases will code for the production of a unique protein
  • It is these proteins and combination of proteins that give us a unique phenotype.


2) DNA replication

  1. The double DNA helix unwinds
  2. Weak hydrogen bonds between nitrogenous bases break and two DNA strands unzip  separate)
  3. Each original DNA strand serves as a template on which its complement is built
  4. Free nucleotides build a DNA strand onto each of the original two DNA strands by attaching to their complementary nitrogenous bases (A to T and C to G)
  5. This results in two identical DNA molecules. Each molecule consists of one original strand and one new strand.




The significance of DNA replication:

  • Important for growth and reparation
  • Mutations in DNA could cause genetic variation


3) DNA profiling

What is DNA profiling?

A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA.  

The process is as follows:

  • The nucleotides are separated from each other in the order that they are found in a strand of DNA
  • Nucleotides appear as dark bands
  • The sequence  of the bases in this segment  is identified
  • Use as DNA fingerprint
  • Unique for every person


What is DNA profiling used for?

  • Solving crimes
  • Paternity tests
  • Identifying bodies


The process followed in paternity cases are:

  1. The potential father, mother and child’s DNA profiles are compared next  to  each other. (All three persons’ DNA bands are on same diagram)
  2. Eliminate all the bands that match the mother
  3. All the remaining bands are compared to the father and if all the remaining bands correspond with the DNA bands of the potential father, he is the biological  father

Below are six different persons’ DNA profiles depicted with the dark bands. You can see who is related by using a ruler to see which bands correspond with each other. There are twins here; can you see who are twins



Solving crimes by using a DNA fingerprint:


  • A useful but controversial method
  • A sample of a suspect’s bodily fluid or tissue is to be compared with a sample found at the scene of a crime
  • The pattern of lines represents a person’s specific genetic make-up
  • DNA fingerprinting used in 11/9 disaster to identify victims


4) RNA
There are three types of RNA molecules, namely messenger RNA (mRNA); transfer RNA (tRNA) and ribosomal RNA (rRNA)

  1. Messenger RNA (mRNA) Has the same sequence of bases as the DNA strand that has the gene sequence.  Acts as a template for protein synthesis

  2. Transfer RNA (tRNA) One for each triplet codon that codes for a specific amino acid. tRNA molecules are covalently attached to the corresponding amino acid at one end. At the other end they have a triplet sequence (called the anti-codon) that is complementary to the triplet codon on the mRNA

  3. Ribosomal RNA (rRNA) Make up an integral part of the ribosome, the protein synthesis machinery in the cell.  (Not examinable)


Last modified: Friday, 12 March 2021, 11:58 AM