1. Higher Human Biology Sub topic 2a
The Structure of DNA
Higher Human Biology
Sub topic 2a

2. Describe the structure of DNA
Learning Intention
Describe the structure of DNA
Explain the base pairing rule using adenine, thymine, cytosine and guanine

3. DNA
Do you remember what DNA stands for? Where is it found? What does it code for?

5. Chromosomes are found in the nucleus.
They are made up of tightly coiled DNA (deoxyribonucleic acid) and proteins.

6. Each nucleotide consists of
A DNA molecule is made up of 2 strands of repeating units called NUCLEOTIDES
Each nucleotide consists of
a 5 carbon deoxyribose sugar
an attached phosphate group
an organic base.

7. A deoxyribose sugar

8. Nucleotide
There are 4 different types of nucleotides. This is because there are 4 different bases: ADENINE THYMINE CYTOSINE GUANINE

10. They are held together by weak hydrogen bonds
Base Pairing
Certain bases are complementary to each other, this is called the base pairing rule.
A pairs with T
C pairs with G
They are held together by weak hydrogen bonds

11. STRONG CHEMICAL BOND links the nucleotides between the phosphate and sugar.
ADENINE
GUANINE

12. The 2 strands are arranged in a twisted coil called a “DOUBLE HELIX”.
It has sugar-phosphate backbone

13. The 2 strands run in opposite directions
- ANTI – PARALLEL
The 5’ (5 prime) end has a phosphate
The 3’ (3 prime) end has a sugar
Nucleotides join on at the 3’ end

14. DNA you tube
Extra DNA revision

15. Inheritance
DNA is important because it is how all cells store genetic information.
The base sequence of DNA determines genotype.
DNA is found in the nucleus of a cell.

16. Chromosomes DNA is arranged in tightly coiled chromosomes.
The DNA is packaged with proteins.

17. Learning Outcomes
The genotype of a cell is determined by the sequence of bases in its DNA.
DNA is the molecule of inheritance and can direct its own replication.
Structure of a DNA nucleotide (deoxyribose sugar, phosphate and base).
Nucleotides bond to form a sugar–phosphate backbone.
Base pairs (adenine, thymine and guanine, cytosine,) are held by weak hydrogen bonds forming a double helix.
The DNA double helix has an antiparallel structure with deoxyribose and phosphate at 3' and 5' ends of each strand.
Chromosomes consist of DNA tightly coiled and packaged with associated proteins.
You should also have looked at experimental work carried out by famous biologists

18. Describe the location and structure of DNA. (8 marks)
DNA is located on chromosomes in the nucleus.
A DNA molecule consists of two strands wound in a double helix.
Each strand consists of subunits called nucleotides.
A nucleotide consists of a deoxyribose sugar molecule, a phosphate group and an organic / nitrogenous base.
The deoxyribose and phosphate are linked to their neighbours to form a sugar-phosphate backbone.
There are four organic bases: adenine (A), thymine (T), guanine (G) and cytosine (C).
Bases are linked in complementary pairs A-T and G-C.
Bases link the two DNA strands by hydrogen bonds.
The two DNA strands have an antiparallel structure / explanation.
Deoxyribose is found at the 3  end of each strand and phosphate is found at the 5  end.