Chapter 16 - Chromosomes, Genes & DNA Flashcards
DNA is…
…the genetic code that determines the characteristics of a living thing.
.. the molecule that holds the instructions for growth and development in every living thing.
DNA = deoxyribonucleic acid…the ‘deoxyribo’ part comes from the sugar in the DNA molecule
A gene is…
a short section of DNA that control the production of proteins in a cell and determine a particular feature.
Each gene codes for a specific protein by specifying the order in which amino acids must be joined together.
Chromosomes are…
…rod shaped bodies found in the nucleus of cells that contain genetic information (DNA)
Draw a diagram to show how dna, cells, the nucleus of a cell and chromosomes fit together….
Who discovered DNA?
Rosalind Franklin started in 1940s/50s (but died) and then James Watson and Francis Crick in 1953 (at Cambridge University)
The structure of DNA…
…made from two strands of nucleotides
(making it a polynucleotide)
Each nucleotide contains:
- A nitrogenous base (either Adenine, Thymine, Cytosine or Guanine)
- A sugar molecule
- A phosphate group
DNA is the only chemical that can…
…replicate itself exactly.
Because of this it’s able to pass on genetic code from one generation to the next
How do the different components of DNA fit together…
DNA is made up of…
…two strands: one = sense strand; one = antisense
Only the sense strand manufactures proteins…
Proteins manufactured can be:
- intracellular enzymes
- exrtracellular enzymes
- structural proteins (e.g. used to make hair, blood, muscles etc)
- hormones
The DNA code is a…
…triplet code…
…a universal code…a base sequence that codes for humans, bacteria, any other organism…even bananas! True.
DNA replication is the process by which…
…a cell makes an identical copy of its DNA.
This process is performed at the beginning of every cell division so that when the cell divides, each daughter cell will inherit an identical copy of the DNA.
3 stages of DNA replication…
Stage one
The DNA is unwound and unzipped. The helix structure is unwound. Special molecules break the weak hydrogen bonds between bases, which are holding the two strands together.
Stage two
DNA polymerase adds DNA nucleotides in a 5’ to 3’ direction. Complementary DNA nucleotides are added to the now exposed bases on both strands. Adenine pairs with thymine, thymine with adenine, cytosine with guanine and guanine with cytosine. A primer is needed to start replication.
Leading strand is synthesised continuously. DNA polymerase adds nucleotides to the deoxyribose (3’) ended strand in a 5’ to 3’ direction.
Lagging strand is synthesised in fragments. Nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction. The lagging strand is therefore synthesised in fragments. The fragments are then sealed together by an enzyme called ligase.
Stage three
The two new strands twist to form a double helix. Each is identical to the original strand.
4 types of Gene mutation…
- Duplication
- Deletion
- Substitution
- Inversions
All mutations are random events that occur in all organisms
The structure of chromosomes….
…each chromosome contains one double-stranded DNA molecule…
…the DNA molecule is folded so it can be packed into a small space.
The DNA is coled around proteins called histones
How many chromosomes?
All human cells contain 46 chromosomes
(not all cells have 46 chromosomes, e.g. blood which has no nucleus)
Can you answer these questions????
