2: Nucleic acids Flashcards
What are the two best known nucleic acids?
RNA and DNA
What are nucleic acids?
Polymers of nucleotides
What is a nucleotide?
The monomer of nucleic acids
What is the composition of a nucleotide?
Pentose sugar
Organic Nitrogenous Base
Phosphate Group
What pentose is found in DNA and RNA?
DNA - Deoxyribose
RNA - Ribose
What is the full name of DNA?
Deoxyribonucleic acid
What is the full name of RNA?
Ribonucleic acid
What does an organic compound mean?
It contains carbon
What are the nitrogenous organic bases?
C - cytosine T - thymine U - uracil A - adenine G - guanine
Where is uracil found and what does it replace?
Found in RNA
Used in stead of thymine
What are the differences between DNA and RNA?
RNA has ribose instead of deoxyribose
Uses the base uracil instead of thymine
How are the components of a nucleotide joined?
Two condensation reactions
What is a single nucleotide called?
Mononucleotide
How can two nucleotides bond together?
Pentose bonds with the phosphate group of another
Condensation reaction
What is the name of the bond that forms between nucleotides?
Phosphodiester bond
this forms the phosphate-sugar backbone
What is the strength of a phosphodiester bond?
Very strong
What is the name of two nucleotides bonded together?
Dinucleotide
What are the uses of RNA?
Transfers genetic info from DNA to ribosomes
Ribosomes are made up of proteins and RNA
Used in protein synthesis
What are the pyrimidine bases?
Thymine
Uracil
Cytosine
What are the purine bases?
Adenine
Guanine
What can excessive nucleic acid cause?
Gout - as purines are broken down into uric acid in liver
What is the structure of DNA?
Two antiparallel polynucleotide strands
Twisted to form a double helix
Strands held together by hydrogen bonds
Bases are paired
What are the base pairs?
Adenine - Thymine (or Uracil)
Guanine - Cytosine
(Purine - Pyrimidine)
What is the name of the pairing of bases?
Complementary Base Pairings
Why do purines have to pair with pyrimidines?
As purines are larger and equal spacing must be maintained
How many hydrogen bonds form between thymine and adenine?
2 Hydrogen bonds
How many hydrogen bonds form between cytosine and guanine?
3 Hydrogen bonds
When does DNA replication occur?
Interphase
Why is DNA used as a hereditary material?
Stable so it can pass from generation to generation without change
Large so carries a lot of info
Order of bases is genetic code and protected in double helix
Hydrogen bonds break easily allowing chains to separate to allow DNA to replicate & protein synthesis
Why is DNA said to be a stable molecule?
Phosphodiester backbone protects more chemically reactive bases
Hydrogen bonds link the organic base pairs forms bridges between the phosphodiester uprights
Why is a DNA molecule more stable with more C-G pairings?
There are 3 hydrogen bonds, so overall the structure is much more stable
What is the function of DNA?
To be the hereditary material that passes genetic information
How is DNA adapted to its function?
Very stable
What does complementary base pairing allow?
The replication and transfer information as mRNA
What does antiparallel mean?
The polynucleotide running antiparallel has its bases projecting inwards as it runs opposite to the other strain (flipped 180)
What are the two stages of cell division?
Nuclear division - nucleus divides (mitosis or meiosis)
Cytokinesis - whole cell divides
Why does DNA replication have to occur before cell division?
To ensure the daughter cells and the parent cells have DNA
What happens if a cell does not have DNA?
It does not have the genetic information to produce proteins
Life is not possible
What is the semi-conservative replication theory?
Half the strands in each new DNA molecule are from the original molecule
What is the conservative replication theory?
The original DNA strands would stay together and the new DNA is composed of new strands
What are the four requirements for DNA replication?
The four types of bases must be present
Both strands of DNA act as template for attachment of nucleotides
Enzymes DNA helicase and polymerase must be present
Source of chemical energy
What is the process of the semi-conservative method?
DNA helicase breaks hydrogen bonds between bases
Causes the strands to separate and unwind
Each exposed strand acts as template, complementary free nucleotides by specific base pairs
Nucleotides join by condensation reaction by enzyme DNA polymerase, making the phosphodiester bonds
Two molecules of identical DNA is produced
What is the product of the semi-conservative method?
Two identical molecules of DNA
They are the same as the original strand
Who did the experiment which proved the semi-conservative method?
Meselsohn and Stahl
What was the Meselsohn & stahl based on?
All bases in DNA contain nitrogen
Nitrogen has two forms
Bacteria will incorporate nitrogen from their growing medium
What are the two forms of nitrogen?
14N - light nitrogen
15N - heavy nitrogen
What is done in the experiment that proves the semi-conservative method?
Bacteria grown in heavy & light nitrogen, then DNA spun in centrifuge. Heavy settles low, light settles high
Then heavy bacteria put into light nitrogen broth, after one round replication another sample is taken
The DNA settles halfway between where the light and heavy settles as the DNA has mixed
What would occur in the Meselsohn & Stahl experiment if the conservative method was true?
The heavy DNA would still be together and new DNA would be light. The centrifuged DNA would be a layer of heavy and light
What is the full name of ATP and what type of molecule is it?
Adenosine Triphosphate
It is a phasphorylated molecule
What is the composition of ATP?
Adenine - a nitrogenous organic base
Ribose - pentose which acts as the backbone
3 phosphates - chain of inorganic ions
What stores energy in ATP?
Bonds between phosphates are unstable and has a low activation energy
When they are broken they release a considerable amount of energy
Which phosphate ion is removed in living cells?
Terminal phosphate
Revise the reaction when a phosphate is removed from ATP
ATP + (H2O) <> ADP + Pi + E
E = energy
What is ADP?
ATP but with 2 phosphate ions
What is Pi?
Inorganic phosphate
What enzyme is used to convert ATP to ADP?
ATP Hydrolase
What enzyme is used to convert ADP to ATP and what is this kind of reaction?
ATP Synthase
Condensation reaction
When does the ADP -> ATP reaction occur?
Photophosphorylation
Oxidative phosphorylation
Substrate-level phosphorylation
Where does Photophosphorylation occur?
Occurs in chlorophyll-containing plant cells during photosynthesis
Where does Oxidative phosphorylation occur?
In plant and animal cells during respiration
Where does Substrate-level phosphorylation occur?
In plant and animal cells when phosphate groups are transferred from donor molecules to ADP
What kind of energy source is ATP?
Immediate energy source of a cell
Why is ATP a better immediate energy source than glucose?
Each ATP molecule releases less energy - energy is released in smaller more manageable quantities for reactions
The hydrolysis of ATP to ADP is a single reaction that releases immediately - glucose takes much longer
Why is smaller release of energy by ATP advantageous?
More manageable quantities for reactions
Why can ATP not be stored?
The instability of the phosphate bonds
Which cells have large number of mitochondria and why?
Muscle fibers (energy for movement) & epithelial cells in small intestine (enterocytes - energy for active transport)
Name 5 energy-requiring processes in which ATP is used
Metabolic processes Movement Active Transport Secretion Activation of molecules
What is a metabolic process?
ATP provides energy needed to build up macromolecules from basic units (polymerisation)
How is ATP used for movement?
ATP provides energy for muscle contraction - provides energy for muscle filaments to slide past and shorten overall muscle fiber length
How is ATP used in active transport?
ATP provides energy to change shape of carrier protein in plasma membranes - allows molecules or ions to move against conc. gradient
How is ATP used in secretion?
ATP is needed to form lysosomes necessary for secretion of cell products (exocytosis)
How is ATP used in activation of molecules?
Inorganic phosphate during ATP hydrolysis can react with other molecules by phosphorylation and make them more reactive
This lowers the activation energy in enzyme-catalysed reaction
What is an example of the activation of molecules?
Glycolysis - Addition of inorganic phosphate to glucose molecules
