Nucleic Acids Flashcards
What does DNA and RNA do in all living cells?
DNA holds genetic information
RNA transfers genetic information from DNA to the ribosomes
What is the polymer of a nucleotide?
Polynucleotide
What is the monomer of a polynucleotide?
Nucleotide
Draw the Nucleotide in DNA
Draw the Nucleotide in RNA
What do DNA nucleotides consist of?
-deoxyribose sugar
-a phosphate group
-a nitrogenous base (Adenine, Cytosine, Guanine or Thymine)
What do RNA nucleotides consist of?
-ribose sugar
-a phosphate group
-a nitrogenous base (Adenine, Cytosine, Gusnine or Uracil)
How are polynucleotides formed?
the removal of water between two nucleotide monomers to form a phosphodiester bond
How are sugar phosphate backbones formed?
-polynucleotides are formed when many nucleotides link to form a long chain
-a phosphodiester bond between the phosphate group of one nucleotide to the 3rd carbon of the deoxyribose/ribose sugar in the next nucleotide
-forms a very strong and stable sugar phosphate backbone
What are the two groups of organic nitrogenous bases?
pyrimidine (single ring) and purine (double ring)
Which bases are pyrimidine?
-thymine
-cytosine
-uracil (ONLY IN RNA)
Which bases are purines?
-adenine
-guanine
What structure does DNA have and what does it consist of in terms of Watson and Crick’s DNA model?
-double helix structure
-consists of 2 polynucleotide chains held together by many weak H bonds between specific complimentary base pairs
How many hydrogen bonds form between the bases?
-two hydrogen bonds between Adenine and Thymine
-three hydrogen bonds between Cytosine and Guanine
What is the sequence of bases along a nucleotide chain?
it is variable
If you are given the % of 1 base how can you work out the rest of the bases?
If Adenine =30% Thymine is also 30% because they are complimentary
Take the total of these away from 100=40%
40/2=20%
Cytosine and Guanine =20% each
What is the function of DNA?
it codes for the sequence of amino acids (3 bases=triplet=1 amino acid)
long strands of DNA code for the primary structure of polynucleotide chains and proteins
How many bases make up 1 amino acid?
3 bases- a triplet
What is mRNA and what does it do?
it is a relatively short polynucleotide chain
it is normally a single stranded helix
-used to transfer genetic information from DNA to ribosomes
How are nucleotide strands arranged in a DNA molcecule?
-adenine pairs with thymine and cystosine with guanine
-the 2 strands run in opposite directions
-antiparallel
-(if the arrow points down, the arrow bit/bottom is the 3 prime end 3’ and the plain bit/the top is the 5 prime)
Why is the 5’ end and the 3’ end of a molecule labelled?
indicated which carbon is involved in the phosphodiester bond
How does the structure of DNA allow it to carry out its function?
-long molecule SO stores lots of information
-helical/coiled SO compact
-many weak H bonds SO DNA is a stable structure
-complimentary base pairs (A-T and C-G) ALLOWS accurate replication
-double stranded SO replication can occur semi conservatively because each strand can act as a template
Which two enzymes are involved in semi conservative replication?
DNA Polymerase + DNA Helicase
What is the role of DNA Polymerase in semi conservative replication?
-catalyses the condensation reaction between DNA nucleotides to form the sugar phosphate backbone of the new strand
What is the role of DNA Helicase in semi conservative replication?
-breaks the hydrogen bonds between complimentary base pairs so each strand can act as a template
(unzips helix)
How does semi conservative replication occur?
- the enzyme DNA Helicase moves along the DNA molecule unwinding the DNA and breaking Hydrogen bonds between base pairs
- the 2 strands seperate
- Each strand acts as a template
- New DNA nucleotides are attracted to exposed complimentary bases on template strands by base pairing
- The enzyme DNA Polymerase joins adjacent nucleotides together through a condensation reaction, forming phosphodiester bonds between new nucleotides in a 5’ to 3’ direction
- semi conservative replication ensures that each new DNA molecule contains an original and a new strand
How does DNA polymerase catalyse a condensation reaction?
-DNA Polymerase has a specific shape active site, only complimentary to the 5’ end of the incoming free DNA nucleotide and the 3’ end of the developing strand
-this catalyses a condensation reaction forming phosphodiester bonds between the last DNA nucleotide in the developing strand (3’) and new incoming DNA nucleotide (5’)
Describe the Messelson & Stahl DNA replication experiment
-used a heavy and a light isotope of nitrogen
-first has 2 N15
-then has 2 lots of N15 and 2 lots of N14 (first generation)
-split again to get 2 lots of n15 and 6 lots of N14 (second gen)
-split again to get 14 lots of N14 and 2 lots of N15 (3rd gen)
Messelson & Stahl
revise in booklet
What does an ATP molecule consist of?
- a ribose sugar
-3 phosphate groups
-an adenine base
How is ATP formed?
-adenine diphosphate+ inorganic phosphate (phosphorylation)
-requires energy to add a phosphate group to ADP to form ATP creating a high energy bond
-involves a condensation reaction and the enzyme ATP synthase
What are the uses of ATP?
-used as energy source in cells to carry out essential life processes (active transport, muscle contraction, protein synthesis)
-Phosphorylation (lowers activation energy making substrates more reactive by altering tertiary structures)
Why is ATP useful?
-releases small amounts of energy
-instant energy source
-phosphorylates other compounds making them more reactive
-can be rapidly resynthesised
-does not leave cells but is soluble
How can ATP return back to ADP and Pi?
-hydrolysed
-bond between the second and third phosphate breaks releasing small managebale amounts of usable energy
-ATP breaks down to ADP and Pi in a hydrolysis reaction (requires a water molecule and ATP Hydrolase)
-Pi can be used to phosphorylate other compounds and make them more reactive
Where is ATP produced?
IN respiration and photosynthesis (NOT FOR THEM)
Draw an ATP molecule
Give 2 ways in which ATP is a suitable energy source for cells to use (2)
-releases small amounts of energy
-releases energy instantaneously
-phosphorylates other compounds making them more reactive
-can be rapidly resynthesised
-does not leave cells
Give 2 ways in which the hydrolysis of ATP is used in cells (2)
-phosphorylates other compounds making them more reactive
-provides energy for active transport/muscle contraction
Describe how ATP is resynthesised in cells (2)
-ADP + Pi
-by ATP Synthase
-In respiration
Contrast the structures of ATP and a nucleotide found in DNA (2)
-ATP has ribose and DNA nucleotides have deoxyribose
-ATP has 3 phosphate groups and DNA nucleotides have 1
-in ATP the base is always adenine but in DNA nucleotides bases change/vary
What are the important properties of water?
-is an important solvent in which metabolic reactions occur
-is a metabolite in many metabolic reactions, including condensation & hydrolysis reactions
-has a relatively high SHC which buffers changes in temp
-large latent heat of vaporisation=cooling effect
-strong cohesion between water molecules which supports columns of water
What type of molecule is water?
dipole/polar
-has 2 slight charges
In water, are electrons equally shared?
no, there is a slight negative charge on oxygen atoms
How does water act as a solvent?
-polar molecules dissolve in water
-more molecules dissolve in water than anything else so it is known as the “universal solvent”
-major component of the cytoplasm as it allows chemicals and enzymes to dissolve
more detailed facts about water
booklet
Give 2 properties of water that are important in biology. Explain the importance of each property you identify (4)
-polar molecule- acts as a universal solvent
-a metabolite- in condensation reactions
-high SHC-reduces fluctuations in temperature
Suggest why water becomes lighter when it expands (2)
-density= mass/volume
-ice has the same mass as water but a greater volume
Suggest one biological advantage of this property of water (density) (2)
-ice is colder than water
-lighter than water so ice floats on water
-reduces freezing of water below ice
Scientists looking for extra-terrestrial life are looking for planets with evidence of free water. Explain why water is considered so important for life to occur (6)
-life is thought to have evolved in water
-water provides support for bodies of organisms
-water is a major component in cytoplasm
-water is a universal solvent
-water is a metabolite (in condensation reactions)
-water stabilises external temperatures
How does an ion form?
when atom loses or gains an electron
Where are inorganic ions found?
in solutions in the cytoplasm and the bodily fluids of organism, some in very high concentrations and some in very low concentrations
What is the function of a hydrogen/ acid ion?
-effects the acidity of solutions (PH)
-H+ is used in respiration to provide energy to make ATP
What is the function of a hydroxide/OH-/ alkali ion?
-H+ used in photosynthesis to provide energy to make ATP
What is the function of an iron ion?
-structural component of haemoglobin (binds O2) to allow the transport of oxygen to respiring tissues
What is the function of a sodium ion?
-used in the co transport of glucose and amino acids
-used in nervous conduction
What is the function of a phosphate ion?
components of phospholipids- DNA, RNA and ATP
What is the function of nitrate ions?
-taken up from the soil by plant roots
-used in making amino acids
what is the function of chloride ions?
-used in regulating the water potential of the small intestine
What are the inorganic ions?
-hydrogen
-hydroxide
-iron
-sodium
-phosphate
-nitrate
-chloride
Why might the gene for a polypeptide contain more than the number of bases? (1)
-there are 2 DNA strands
What is the name of the bond between nucleotides?
phosphodiester
The enzymes DNA Helicase and DNA polymerase are involved in DNA replication. Describe the function of each of these enzymes (2)
DNA Helicase- unzips complimentary base pairs so strands can seperate and act as templates
DNA Polymerase- Joins adjacent nucleotides
Explain why the arrows in DNA strand production point in opposite directions (3)
-DNA has antiparallel strands
-enzymes have active sites with a specific shape
-only substrates with complimentary shapes can bind to the active site
Explain why new nucleotides can only be added in a 5’ to 3’ direction after strands seperate to act as templates (4)
-DNA Polymerase
-is specific
-only complimentary to the 5’ end
-shape of the 5’ end and 3’ end are different
Describe the role of DNA polymerase in DNA replication (1)
-joins adjacent nucleotides to catalyse a condensation reaction
Other than being smaller, give 2 ways in which prokaryotic DNA is different to eukaryotic DNA (2)
-prokaryotic is circular
-prokaryotic does not associate with proteins/ histones
Use your knowledge of DNA structure and function to explain how humans and grasshoppers have a similar percentage of each base in their DNA but are very different organisms (2)
-have different genes
-as triplets are in a different sequence
Give two features of DNA and explain how each one is important for semi conservative replication of DNA (2)
-2 strands so each acts as a template
-weak H bonds between complimentary base pairs so it can unzip easily
Explain why DNA helicase is important in DNA replication (2)
-breaks the hydrogen bonds between complimentary base pairs
-so each strand can act as a template
Name the 2 scientists who proposed models of the chemical structure of DNA and of DNA replication (1)
Watson and Crick
Describe how a phosphodiester bond is formed between 2 nucleotides within a DNA molecule (2)
-formed by a condensation reaction
-between the phosphate group of one nucleotide -to the third carbon of the deoxyribose sugar in the next nucleotide
Describe how the separation of strands occurs in semi conservative replication (2)
-DNA Helicase
-unwinds the DNA and breaks hydrogen bonds between complimentary base pairs
Describe the biochemical test to show that a solution contains a non reducing sugar (3)
-add benedict’s and it should give a negative result (stay blue)
-boil it with an acid then neutralise with an alkali
-if NRS is present it should form a red/orange precipitate
State and explain the property of water that can help to buffer changes in temperature (2)
High SHC can buffer changes in temperature (keep the same temp) as it takes more energy to heat water than air
Name 2 products of ATP hydrolysis
-ADP
-Pi
(adenosine diphosphate and inorganic phosphate)
Why is ATP useful in so many biological processes (4)
-releases energy in small manageable amounts
-instant energy source
-phosphorylates other compounds to lower activation energy
-easily reformed
Describe the chemical reactions involved in the conversion of monomers to polymers and polymers to monomers with named examples (5)
-condensation reaction/ loss of water joins monomers together and releases water and forms a bond
-a hydrolysis reaction breaks a chemical bond between monomers using water
-polymers must contain many monomers
-beta glucose &cellulose
-amino acids &polpeptides
