1. 4c: DNA & Proteins
• Describe the location, structure and function of DNA
• Identify the relationship between genes and proteins
• Identify the functions of different proteins
• Describe the process of protein synthesis
2. DNA Structure
• DNA = Deoxyribonucleic Acid
• Contains all the instructions for a
cell
• Shape is a double helix (twisted
ladder)
• Sides of the ladder are alternating
sugar (deoxyribose) and phosphate
• Rungs of the ladder are nitrogen
bases
• The repeating unit of a sugar,
phosphate and nitrogen base is
called a nucleotide.
3. DNA Structure
• There are four nitrogen bases:
• Adenine (A), Cytosine (C), Guanine (G), Thymine (T)
• Bases form bonds in what is known as complementary base
pairing
• A always pairs with T
• C always pairs with G
• Complementary bases will always exist in
equal amounts
• Question: If 15% of a DNA molecule consists
of thymine, what are the percentages of the
other bases?
4. DNA Structure
• There are four nitrogen bases:
• Adenine (A), Cytosine (C), Guanine (G), Thymine (T)
• Bases form bonds in what is known as complementary base
pairing
• A always pairs with T
• C always pairs with G
• Complementary bases will always exist in
equal amounts
• Question: If 15% of a DNA molecule consists
of thymine, what are the percentages of the
other bases?
• Answer:15% T, 15% A, 35% C, 35% G
5. DNA Structure
• The instructions for the cell are written in the genetic code
• Based on the arrangement of the nitrogen bases along a DNA
molecule
• Question: What is the complementary strand of DNA to:
A T G T G C A A C G T G C A
6. DNA Structure
• The instructions for the cell are written in the genetic code
• Based on the arrangement of the nitrogen bases along a DNA
molecule
• Question: What is the complementary strand of DNA to:
A T G T G C A A C G T G C A
T A C A C G T T G C A C G T
7. Organization of DNA
• DNA is contained in the nucleus of a cell
• When a cell is not dividing (which is most of the time), the
DNA is in a loose arrangement of DNA and proteins called
chromatin
• During cell division the DNA must condense into X- shaped
structures called chromosomes
• Half a chromosome is called a chromatid which are held together
at the centromere
8. Chromosomes
• Chromosomes exist in pairs in the nucleus
• Humans have 23 pairs of chromosomes
(46 in total)
• One pair is unusual – Sex chromosomes
• XX = Female XY = Male
9. Genes
• Genes are small segments of DNA (hundreds to thousands of
bases) located at specific locations along the length of a
chromosome
• Every chromosome consists of one DNA molecule made of
thousands of genes
• A gene can store the information to produce 100 000 different
proteins
10. Proteins
• Each cell in the body contains the same genetic information
• Only certain genes in each cell are activated to produce
proteins specific to that cells function
• Proteins are large molecules that are essential for cells to
carry out their functions
• Some protein types:
• Hormones: Chemical messengers in and between cells
• Enzymes: Speed up chemical reactions in a cell
11. Protein Production
1. Nucleus receives signal to produce a specific
protein
2. DNA message is copied to RNA
3. RNA leaves nucleus through a nuclear pore
4. RNA delivers message to ribosome which
makes the protein
5. Protein enters the endoplasmic reticulum
6. Vesicle carries protein from ER to Golgi body
7. Golgi body repackages protein for transport
out of the cell
8. Vesicle carries protein to the cell membrane
9. Protein is released out of cell
