Nucleic acids Flashcards
Structure of nucleotide
- pentose sugar (5 carbons), a phosphate group and a nitrogen containing organic base.
- joined together by condensation reaction
- bases either A,T,C,G OR U
Describe the structure of RNA
- single stranded, relatively short polymer of nucleotides joined by phosphodiester bonds.
- pentose sugar is always a ribose sugar
- bases = G,C, A, U
Describe DNA structure
- polymer of nucleotides joined by phosphodiester bonds
- pentose sugar is deoxyribose
- organic bases = A,T,G ,C
-Made up of 2 strands of nucleotides (polynucleotides). Each of the 2 strands is very long and are joined together by H bonds formed between bases
-double strand twists into a double helix
Describe the events which take place during DNA replication.
1.Strands separate / H-bonds break
2.DNA helicase (involved)
3.Each strand acts as ) template
4.Free nucleotides attach;
5. Complementary base pairing
6.DNA polymerase joins nucleotides
7.H-bonds reform
8. Semi-conservative replication
name the type of reaction that joins two nucleotides together.
condensation reaction
state the location of the new chemical bond that is formed when two nucleotides are joined together.
between the phosphate group of one nucleotide and the sugar of another
name the bond formed when two nucleotides are joined together.
phosphodiester bond
the chain for sugar and phosphates in a polynucleotide is collectively known as what?
sugar-phosphate backbone
what is the advantage of DNA being a helix shape?
DNA is a very long molecule, the helix shape (twisting) allows a lot of genetic information to be stored in a small space - nucleus
the two polynucleotide strands in a DNA molecule are antiparallel. what does this mean?
they run in opposite directions.
if in a section of DNA, 33% of the bases were A, what % of the bases are T? explain your answer
33% are T because number of A is equal to the number of T
if in a section of DNA 33% of the bases were A, what % of the bases are G?
A=T, so 33+33 = 66% of base are A&T. 100-66=34. so 34% of the bases are G and C. so %G = 34/2 = 17%
what is the role of DNA helicase in DNA replication?
breaks the hydrogen bonds between bases causing the strands to separate.
what happens once the DNA double helix has separated into two separate strands?
each strand acts as a template strand. free floating DNA nucleotides match up using complementary base pairing.
What is the role of DNA polymerase?
to catalyse the joining together of adjacent nucleotides on the new strand by condensation reactions, resulting in the formation of a phosphodiester bond.
why is DNA polymerase only complementary to the 3’ end of a DNA strand?
DNA polymerase is an enzyme. enzymes are specific to one substrate. DNA polymerase has an active site with a specific shape that is only complementary in shape to the 3’ end of a DNA strand.
Events that take place during DNA replication
-unwinding of DNA’s double helix structure through DNA helices breaking H bonds between base pairs
-free nucleotides bind to complementary bases
-DNA polymerase builds the polynucleotide by forming phosphodiester bonds by a condensation reaction
Describe the formation of a new polynucleotide strand.
A new polynucleotide strand is formed when DNA polymerase forms phosphodiester bonds between the phosphate on one nucleotide and the sugar on another
How is DNA adapted to carry out it’s functions
-Stable due to many H bonds between bases and these being protected by sugar phosphate backbone
-H bonds between strands > easy to seperate from replication molecule
- large molecule > carry huge amount of info
-base pairing > DNA can transfer information as RNA
Describe complementary base pairing
- Adenine always pairs with thymine
- Guanine always pairs with cytosine
- H bonds between the bases
- 3 H bonds between C and G/2 H bonds between A and T
Explain semi-conservative process of DNA replication
-DNA helices breaks H bonds between base pairs, causing double helix structure to unwind
-free nucleotides bind to complementary bases on the exposed polynucleotide
-DNA polymerase builds up the polynucleotide by forming phosphodiester bonds (condensation reaction)
-2 new polynucleotide chains are formed. Each strand has half the original genetic material
Explain the semi conservative process of DNA replication.
DNA replication is semi conservative because each of the new strands contains one of the original strands
Explain why the process of DNA replication is described as semi-conservative
replicated DNA has 1 original strand and 1 new strand
If and inhibitor of DNA polymerase were introduced into a cell, explain what the effect would be on DNA replication
-regardless on type of inhibitor, enzyme substrate complex wouldn’t form
-so condensation reaction needed to bind nucleotides together wouldn’t occur
-so DNA replication wouldn’t happen
Define what energy is
and why organisms need
it
- Energy is the ability to do work.
- Organisms need energy to live - to carry out metabolic processes, move, maintain temperature etc.
- The energy in organisms originally comes from the sun and is converted to organic molecules by photosynthetic organisms
Explain how ATP stores
energy
- ATP is a nucleotide + consists of an adenine base, ribose sugar and 3 phosphate molecules
- bonds between phosphate groups are unstable > low a.e. so when they’re broken they release energy
- ATP hydrolase catalyses the removal of the terminal phosphate group for ADP by hydrolysis
Describe how ATP is synthesised
- ATP synthase catalyses the reaction to add an inorganic phosphate group to ADP to produce ATP
- condensation reaction
Describe the role of ATP
in biological processes.
ATP is an immediate energy source, that cannot be stored in large quantities, it is formed when required mainly in mitochondria. ATP is required for:
- metabolic processes > builds macromolecules from their basic units
- movement > muscle contraction > provide energy for filaments of muscle to slide past one another > shorten overall length of muscle fibre
- active transport > change shape of carrier proteins in plasma membranes >molecules could be moved against a conc gradient
- secretion > from lysosomes necessary for secretion of cells
- activation of molecules >phosphorylate other compounds to make them more reactive
ATP formula
ATP + H20 > ADP + Pi + E
Describe the structure of water
- Water consists of two atoms of hydrogen and one of oxygen.
- It is dipolar - no overall charge but oxygen is slightly negative and hydrogen slightly positive (the charge is unevenly distributed)
State the properties of water
- H bonds > negative pole of one molecule is attracted to the positive pole of another
- high specific heat capacity > due to hydrogen bonding more energy is required to heat water. Water acts as a buffer against sudden temperature variations
- latent heat of vaporisation > due to hydrogen bonding it takes a lot of energy to evaporate water. effective means of cooling as body heat i8s used to evaporate water
- cohesion > due to hydrogen bonding water molecules stick together.
surface tension, water surface acts like skin and is strong enough to to support small organisms
Explain the importance of the
water molecule to living
organisms.
Metabolism - hydrolysis and condensation reactions/ reactions take
place in an aqueous medium/ raw material for photosynthesis
Solvent - water dissolves other substances eg gases oxygen, carbon
dioxide/ waste eg ammonia and urea/ inorganic ions and small
hydrophilic molecules eg amino acids, monosaccharides, ATP/enzyme
reactions take place in solution)
Other – evaporation cools organisms/ provides support as not easily
compressed/transparent so aquatic plants can photosynthesise
Describe inorganic ions and their roles.
-An inorganic ion is a charged atom that does not contain carbon
Roles:
Iron ions - Haemoglobin, oxygen transport
Phosphate ions - DNA, structural. ATP, energy store.
Hydrogen ions - pH and therefore enzyme function.
Sodium ions - glucose and amino acid transport across membranes. Nerve impulses
