Chapter 2 - Nucleic acids Flashcards
Name 5 useful properties of water
It is an important metabolite High latent heat of vaporisation Buffers changes in temperature Good solvent Strong cohesion between water molecules
What makes water a good metabolite?
Many metabolic reactions involve a condensation or hydrolysis reaction (where water is produced as a new bond is formed or used to break an existing bond)
Why is it important that water is a good metabolite?
Amino acids are joined together to make polypeptides in condensation reactions
Why does water have such a high latent heat of vaporisation?
It takes a lot of energy to break the hydrogen bonds between water molecules
When water molecules evaporate from a body of water, they take a lot of energy with them
So the body of water cools down
Why is it important that water has such a high latent heat of vaporisation?
Animals can keep cool by sweating and plants cool down when water evaporates from leaves
Why does water have such a high specific heat capacity?
The hydrogen bonds between water molecules can absorb a lot of energy so it absorbs a lot of heat energy before a significant change in temperature occurs
Why is it important that water has such a high specific heat capacity?
It makes aquatic environments great habitats because the temperature is stable
Water buffers temperature changes inside our bodies so our internal body temperature is constant
Why is water such a good solvent?
Many compounds are ionic (they consist of one positively charged ion and one negatively charged one)
Because water is polar, the positive end of it will attach to the negative end of the compound and vice versa
This means the compound will get surrounded by water molecules and will eventually dissolve
Why is it important that water is such a good solvent? (2)
Many reactions inside the body can only happen when the reactants are dissolved in water
Dissolved substances like glucose can be transported around body
Why are water molecules so cohesive?
They are polar molecules so hydrogen bonds form between the differently charged ends of the molecule
Importance of water’s strong cohesion 2
Water flows so it is great for transporting substances
Surface tension means small insects can live on surface
Describe the structure of water
The shared hydrogen electrons are pulled to one side of the hydrogen atoms, leaving the other side with a slight positive charge
The unshared electrons on the oxygen give it a slight negative charge
These different charges make it a polar molecule
The slightly negative oxygen atoms join to the slightly positive hydrogen ones
These are called hydrogen bonds
What is one nucleotide made out of?
A pentose sugar
A phosphate group
A nitrogen-containing organic base
Function of DNA
It stores all the genetic information we need to grow and develop
Function of RNA
It transfers genetic information from the nucleus to the ribosomes
What are the four bases in DNA?
Adenine, Thymine, Guanine, Cytosine
What pentose sugar is found in DNA?
Deoxyribose
What are the four bases on RNA?
Adenine, Uracil, Guanine, Cytosine
What pentose sugar is found in RNA?
Ribose
What is a polynucleotide?
A polymer made of numerous nucleotides
How do the sugar, base and phosphate group join together?
A condensation reaction occurs between the sugar and phosphate group
How is a polynucleotide formed?
A condensation reaction occurs between the sugar of one DNA group and the phosphate group of another, forming a phosphodiester bond
What bond is formed when two nucleotides join?
Phosphodiester
How are the two strands of DNA held together?
Hydrogen bonds
What are the complimentary base pairs?
Adenine - Thymine
Cytosine - Guanine
How many hydrogen bonds form between A and T?
Two
How many hydrogen bonds form between C and G?
Three
What does antiparallel mean?
The two DNA strands run in opposite directions
Why is DNA very stable?
The phosphodiester backbone protects the more reactive organic bases, and the hydrogen bonds between complimentary bases are strong
Why is DNA said to be antiparallel?
The enzyme DNA polymerase can only attach nucleotides to the 3’ carbon on the DNA molecule
What name is given to the current theory on DNA replication?
The Semi-Conservative model
What does the enzyme DNA helicase do?
Breaks hydrogen bonds between the base pairs
What does the enzyme DNA polymerase do?
Joins activated nucleotides together
What is the Semi-Conservative model of DNA replication?
DNA helicase breaks the hydrogen bonds, so the strands of DNA split apart.
Each exposed strand then acts as a template for the new strand
Complimentary base pairing means that free-floating bases are attracted to their exposed complimentary bases on the template strand
DNA polymerase joins the two strands together in a condensation reaction, forming hydrogen bonds
Each new strand of DNA contains one strand from the original DNA molecule and one new strand`
What is the structure of a molecule of ATP?
Contains adenine, ribose and a chain of three phosphate groups
How does ATP store energy?
Between the three phosphate groups, there are weak bonds, with a low activation energy. When they are broken, a lot of energy is released in a hydrolysis reaction
What is produced when ATP is hydrolysed?
ADP + P + energy
Which enzyme catalyses the reaction of ATP to ADP?
ATP hydrolase
What is special about the use of ATP?
It is reversible - energy can be used to add a phosphate to ADP to make ATP
What enzyme is used to made ATP from ADP?
ATP synthase
What can the phosphate group released when ATP releases energy be used for?
It can join to another compound to make it more reactive
Why is ATP only a short-term energy source?
The bonds between phosphates are very unstable
Why is ATP a better energy source than glucose? (2)
Energy is released in much smaller, more manageable amounts
The hydrolysis of ATP to ADP is a single reaction that releases immediate energy
5 uses of ATP
Metabolic processes Movement Active transport Secretion Actvation of molecules
How is ATP used in metabolism?
It provides the energy to make larger molecules from their units
How is ATP used in movement?
It provides the energy for muscle contraction
How is ATP used in active transport?
It provides the energy for proteins to change shape
How is ATP used in secretion?
It creates the lysosomes necessary for secretion
How is ATP used to activate molecules?
The phosphate produced can make other molecules more reactive
What did Meselson and Stahl do?
Provide evidence for semi-conservative DNA replication
What was Meselson and Stahl’s experiment?
They grew two samples of bacteria - one in heavy and one in light nitrogen. When placed in a centrifuge, heavy nitrogen would settle at the bottom and light nitrogen would float. At the end of the experiment, the bacteria floated in the middle, showing they had taken DNA from both types of nitrogen
What is an ion with a positive charge called?
A cation
What is an ion with a negative charge called?
An anion
What is special about an inorganic ion?
It doesn’t contain any carbon
Where are iron ions found?
Haemoglobin
What are hydrogen ions used for?
Determining pH
What are sodium ions used for?
Co-transport
What are phosphate ions used for?
Bonds between phosphates in ATP store up energy
