DNA Flashcards
What makes up a nucleotide?
- a deoxyribose sugar
- a nitrogen containing organic base
- a phosphate group
What makes up an RNA nucleotide?
- a ribose sugar
- a phosphate group
- a base
What reaction joins two nucleotides together by the phosphate group of one and the sugar of another? What bond is formed?
- a condensation reaction
- a phosphodietser bond
What bonds are between the bases?
Hydrogen bonds
How many hydrogen bonds form between adenine and thymine?
Two hydrogen bonds
How many hydrogen bonds form between the C and G base?
Three hydrogen bonds
Name the bases in RNA
Uracil, adenine, cytosine and guanine
How does DNA replicate itself?
Semi-conservative replication
Describe semi-conservative replication:
1) DNA helicase breaks th hydrogen bonds in order to unwind the double helix.
2) Each original strand acts as a template for a new strand.Free-floating complementary bases are attracted to the exposed bases on each original template strand.
3) Condensation reactions join the nucleotides of the new strands together catalysed by DNA polymerase.Hydrogen bonds form between the bases on the new strand and the original strand.
How did Meselon and Stahl prove semi-conservative replication?
1) two sample of bacteria were grown one in a nutrient broth containing light nitrogen and another in heavy nitrogen.
2) A sample of each DNA was taken from each bacteria and spun in a centrifuge.The DNA from the heavy nitrogen settled lower down in the centrifuge.
3) Then the bacteria grown in the heavy broth were taken out and put in the light broth.The bacteria were left for one round of DNA replication.
4) This DNA settled in the middle of the centrifuge as it has one stand of light DNA and one strand of heavy DNA.
What does mitosis produce?
two genetically identical daughter cells
What id mitosis needed for?
growth and reparation
What is the order of the cell cycle and what happens at each stage?
1) G1 phase- cell grows and new organelles and proteins are made.
2) S phase- the cell replicates its DNA ready to divide by mitosis.
3) G1 phase- cell keeps growing and and proteins needed for cell division are made.
4) Mitosis.
Describe mitosis:
1) INTERPHASE- the cell prepares to divide, the cells DNA is unravelled and replicated.The organelles are replicated and ATP content is increased.
2) PROPHASE- chromosomes condense getting shorter and fatter.Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it causing the spindle.The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.
3) METAPHASE-The chromosomes line up along the equator and become attached to the spindle by their centromere.
4) ANAPHASE-The centromeres divide, separating each pair of opposite chromatids to opposite poles of the spindle.
5) Telophase- chromatids reach opposite poles on the spindle.They uncoil and become long and thin again.A nuclear envelope forms round each group of chromosomes.The cytoplasm divides (cytokinesis)
mitotic index equation
mitotic index=number of cells with visible chromosomes/total number of cells observed.
