What does DNA stand for?
Deoxyribonucleic acid
What is extranuclear DNA?
Small amounts of DNA that are found:
- outside the nucleus in mitochondria (in plants & animals)
- in chloroplasts (in plants)
What is the shape of DNA like?
- a long, twisted ladder
- the two strands twist to form a stable, 3-dimensional double helix
What is a DNA molecule made up of?
- a long chain (polymer), which is made up of small units (monomers)
- ie, building blocks called nucleotides
What is a nucleotide made up of?
- sugar molecule - deoxyribose (S)
- phosphate molecule (P)
- nitrogenous base
What are the different nitrogenous bases?
- adenine (A)
- thymine (T)
- guanine (G)
- cytosine (C)
What is the importance of the four nitrogenous bases?
- these are the foundation of the genetic code
- they instruct cells on how to synthesise enzymes and other proteins
How are the outer two strands of the ladder of the double helix made up?
- formed by a chain of alternating sugar/phosphate links
- the bonds between the sugar and phosphate molecules are strong
How are the rungs of the ladder of the double helix made up?
- formed from pairs of bases linked by weak hydrogen bonds
- the base pairs are attached to the sugar molecules
How do the four nitrogenous base pairs link up?
- adenine with thymine or uracil, using 2 hydrogen bonds
- cytosine with guanine, using 3 hydrogen bonds
What are the different groups in which nitrogenous base pairs are classified?
- purines
- pyrimidines
What are purines made up of?
- two fused rings of nitrogen, carbon and hydrogen atoms
Which nitrogenous bases are classified as purines?
- guanine
- adenine
What are pyrimidines made up of?
- one ring of similar atoms
- (therefore much smaller than purines)
Which nitrogenous bases are classified as pyrimidines?
- thymine
- cytosine
- uracil
What are the two main constituents of base pairs?
- one purine and one pyrimidine
Do the nitrogenous bases differ in different organisms?
No, these four nucleotides are the same in all animals and plants.
How do nucleotides in organisms differ?
- they differ in terms of the sequence in which the nucleotides are strung together
What determines the genetic code of an organism?
- the sequence of the nucleotides
What is the role of DNA in terms of carrying information?
- to carry hereditary information in each cell in the form of genes
What is the role of DNA in terms of providing a blueprint?
- to provide a blueprint for an organism’s growth and development by coding for protein synthesis
What is the role of DNA in terms of replication?
- can replicate so that a copy of the genetic information is passed on to each daughter cell formed during cell division
- this ensures that the genetic code is passed on from generation to generation
How much of human DNA codes for proteins?
- less than 2%
- the rest consists of non-coding DNA
What are the protein-coding regions of a DNA molecule called?
- exons
