More Biological Molecules AS Flashcards
DNA and RNA are both types of _______ _____
nucleic acid
What is the role of DNA?
used to store genetic information
What is the role of RNA?
transfer genetic information from the RNA to the ribosomes
Ribosomes read the RNA to make polypeptides in a process called translation
Molecules of DNA and RNA are polymers of _______
nucleotides
What is a nucleotide composed of?
A pentose sugar
A nitrogen containing organic base
A phosphate group
How is a polynucleotide formed?
Nucleotides joined together via a condensation reaction between the phosphate group of one nucleotide and the sugar of another.
This formed a phosphodiester bond
The chain of phosphates and sugars is known as the sugar-phosphate backbone
Describe DNA structure
Double helix structure - formed from 2 separate strands of polynucleotides
The two polynucleotide strands are antiparallel - they run in opposite directions.
DNA molecules are really long and coiled up tightly so a lot of genetic information can fit into a small space in the cell nucleus
What is DNA nucleotide structure?
Phosphate group, pentose deoxyribose sugar and a nitrogen containing organic base
Base can change
can be either
A, T, C, G
What is complimentary base pairing?
Two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base only has one complimentary partner.
A-T
C-G
Two hydrogen bonds form between A-T
Three hydrogen bonds form between C-G
DNA vs RNA
- Sugar in RNA is ribose sugar not deoxyribose sugar
- Uracil replaces thymine as a base
- The nucleotides form a single polynucleotide strand not a double one
- RNA strands are much shorter than most DNA polynucleotides
Why does DNA replicate?
DNA copies itself before cell division so that each new cell has full amount of DNA. This method is called semiconservative replication because half of the strands in each new DNA molecule are from the original DNA molecule.
Explain DNA replication
- The enzyme DNA helicase breaks down the hydrogen bonds between bases on the two polynucleotide DNA strands. This makes the helix unwind to form 2 single strands.
- Each original strand acts as a template strand for a new strand. Complimentary base pairing means that free DNA nucleotides are attracted to their complimentary exposed bases on each original template strand
- Condensation reactions join the nucleotides of the new strand together - catalysed by the enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strand
Describe the action of DNA polymerase
During DNA replication the active site of DNA polymerase is only complimentary to the 3’ end of the newly forming DNA strand - so the enzyme can only add nucleotides to the new strand at the 3’ end. This means that the new strand is made in a 5’ to 3’ direction and that DNA polymerase moves down the template strand in 3’ to 5’ direction.
Because the strands in the double helix are anti parallel, the DNA polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.
Explain Meselson and Stahl’s experiment
Used 2 isotopes of nitrogen
- Two samples of bacteria were grown, one in a nutrient broth containing light nitrogen and one containing heavy nitrogen. As the bacteria grew and reproduced, they took up the broth to help make nucleotides so nitrogen is becoming a part of the DNA
- A sample of DNA was taken from each bacteria. The DNA from heavy nitrogen broth settled lower in the centrifuge tube than the lighter nitrogen broth bacteria
- Then the bacteria grown in heavy nitrogen broth was taken out and put in a broth containing only light nitrogen. The bacteria were left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge
- If replication was conservative the original heavy DNA would settle at the bottom and new light DNA would settle at the top
- If replication was semi-conservative, the new bacterial DNA molecules would contain one heavy strand and one light strand. So the DNA would settle between where light and heavy would have settled.
- The DNA settled in the middle showing the replication is semi conservative
Why is energy important?
Plants need energy for things like active transport, DNA replication, cell division and protein synthesis
Animals need energy for things like active transport(e.g. absorb glucose from the ileum epithelium into the bloodstream), DNA replication, cell division and protein synthesis