Unit 1.5 - Nucleic acids Flashcards Preview

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Flashcards in Unit 1.5 - Nucleic acids Deck (71)
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Monomer of nuclei acid compromising a pentose sugar, nitrogenous base and a phosphate group.


Pyrimidine bases

Class of nitrogenous bases including thymine, cytosine and uracil.


Purine bases

Class of nitrogenous bases including adenine and guanine.


What does a nucleotide consist of?

Phosphate group, ribose in RNA/ deoxyribose in DNA, nitrogenous base.



Organism that uses chemical energy to make complex organic molecules.



Organism that uses light energy to make complex organic molecules, its food.


Adenosine triphosphate (ATP)

Nucleotide in all living cells; hydrolysis makes energy available and its formed when chemical reactions release energy.


State an example of chemoautotrophic organisms.

Some bacteria and Archaea use energy derived from oxidation of electron donors e.g. H2, Fe 2+.


State an example of photoautotrophic organisms.

Green plants use light energy in photosynthesis.


State an example of heterotrophic organisms.

Animals derive their chemical energy from food.


1) When is ATP synthesised?
2) When is it broken down?

1) Energy is made available such as in mitochondria.
2) By ADP when energy is needed such as muscle contraction.


What is ATP called? Explain why.

Universal energy currency because it's involved in all cells in all living organisms.


1) What does adenosine contain?
2) What does ATP contain?

1) Adenine + Ribose
2) Adenine + Ribose + 3 phosphate groups


1) What happens when ATP is needed?
2) How does ADP form?

1) Enzyme ATPase hydrolyses bond between 2nd and 3rd phosphate group, removing 3rd group.
2) ATP molecule hydrolyses into adenosine diphosphate and an inorganic phosphate ion.


1) Define exergonic reaction.
2) How much energy is released in breakdown of ATP?
3) What is the word equation for the breakdown of ATP?

1) Releases energy (ATP hydrolysis).
2) Endergonic 30.6kJ, Exergonic -30.6kJ.
3) ATP + Water > hydrolysis (muscles) > ADP + P
Opposite for condensation (mitochondria).


1) Define endergonic reaction.
2) How do organisms release energy?
3) Define phosphorylation.

1) Requires energy input.
2) Respiration producing ATP.
3) Addition of a phosphate group (e.g. to ADP).


State an advantage of the following over glucose:
1) Hydrolysis of ATP to ADP
2) Enzymes

1) Hydrolysis of ATP to ADP single reaction, releases energy immediately however breakdown of glucose involves intermediates and takes longer for energy release.
2) Only one enzyme needed to release energy from ATP but many are needed from glucose.


State 2 advantages of ATP over glucose.

1) ATP releases energy small amounts, where and when needed (less waste) but glucose has large amounts and releases all at once.
2) ATP common source of energy for different chemical reactions, increasing efficiency and control by cell.


1) What happens when a phosphate group is transferred from ATP to another molecule?
2) What effect does this have on the activation energy?

1) Recipient molecule more reactive.
2) Lowering activation energy of a reaction.


State 5 roles of ATP.

Metabolic processes, active transport, movement, nerve transmission and secretion.


State the role of ATP in:
1) Metabolic processes
2) Active transport

1) Build large complex molecules from small simple molecules e.g. DNA synthesis from nucleotides, proteins from amino acids.
2) Change shape of carrier proteins in membranes allow molecules or ions to be moved against a concentration gradient.


State the role of ATP in:
1) Movement
2) Nerve transmission
3) Secretion

1) Muscle contraction, cytokinesis.
2) Sodium-potassium pumps actively transport sodium and potassium ions across the axon membrane.
3) Packaging and transport of secretory products into vesicles in cells.


1) What is DNA composed of?
2) What forms the 'backbone'?

1) 2 complementary polynucleotide strands in a double helix held together by hydrogen bonds. (4 organic bases).
2) Deoxyribose sugar and phosphate groups are on outside of DNA molecule.


1) Why do the base strands face inwards?
2) State number of hydrogen bonds in adenine and thymine.
3) State number of hydrogen bonds in cytosine and guanine.

1) Due to the rings.
2) Joined by 2 H bonds.
3) Joined by 3 H bonds.


1) How big is the double helix?
2) How are the nucleotides arranged in the strands?

1) 2nm in diameter
2) Antiparallel; running parallel but facing in opposite directions.


1) State the function of the sugar phosphate.
2) Why are 2 strands of DNA able to separate?

1) Base pairs on inside of double helix, within deoxyribose phosphate backbones, genetic information is protected.
2) Held together by hydrogen bonds.


State 2 advantages of DNA.

1) Very stable, information content passes essentially unchanged from generation to generation.
2) Large molecule so carries large amount of genetic information.


Genetic code

DNA & mRNA base sequences determine the amino acid sequences in an organism's proteins.



Group of 3 bases on tRNA molecules, correlated with specific amino acid carried by that tRNA.


1) What sugar does RNA contain?
2) State the components of the purine and pyrimidine bases.

1) Pentose sugar - ribose.
2) Purine - Adenine and Guanine
Pyrimidine - Uracil and Cytosine


1) Where is messenger RNA synthesised?
2) What is the role of mRNA?

1) Long single stranded molecule synthesised in the nucleus.
2) Carries genetic code from DNA to ribosomes in the cytoplasm.


1) Where is ribosomal RNA found?
2) What are ribosomes made from?
3) What is their function?

1) Cytoplasm, large complex molecules.
2) Ribosomal RNA and protein.
3) Site of translation of genetic code into a protein.


1) Describe the structure of transfer RNA. (H bonds between pairs)
2) What does it carry?
3) What is its function?

1) Small single stranded molecule which folds do base sequences form complementary pairs.
2) Anticodon - sequence of 3 bases.
3) Transport specific amino acids to the ribosomes in protein synthesis.


Describe the differences for DNA & RNA for the following:
1) Pentose sugar
2) Pyrimidine bases
3) Strands
4) Length

1) Deoxyribose, Ribose.
2) Cytosine & Thymine, Cytosine & Uracil.
3) 2 in double helix, single-stranded.
4) Long, tRNA & rRNA short but mRNA varies (still shorter than DNA).


Who proposed the molecular structure of DNA?

Watson and Crick in 1953.


1) What is the diameter through the middle of the nuclear pores?
2) How does this affect the chromosomes?
3) What does this allow for DNA?

1) 5-10 nm.
2) Too large to pass through to carry code to ribosomes to be translated.
3) DNA transcribed to form single-stranded RNA, which can pass through.


1) Where is DNA enclosed?
2) Where is DNA loose?

1) Nuclei of eukaryotic cells.
2) Cytoplasm of prokaryotes.


Describe how DNA can be used for replication.

If 2 complementary strands are separated, 2 identical double helices form as each parent strand acts a template for synthesis of new complementary strand.


Describe how DNA can be used for protein synthesis.

Sequence of bases represents the information carried in DNA and determines sequence of amino acids in proteins.


Semi - conservative replication.

Mode of DNA replication in which each strand of a parental double helix acts as template for formation of new molecule containing one parent strand and one complementary daughter strand.



Molecule of which chemical structure determines chemical structure of another molecule.


Conservative replication.

Parental double helix remains intact , whole new double helix is made.


Dispersive replication.

2 new double helices contain fragments from both stands of the parental double helix.


When does DNA replication take place?

Nucleus during interphase.


1) How was conservative replication ruled out in the Meselon-Stahl experiment?
2) Why?

1) DNA from 1st generation centrifuged, mid point density.
2) Produce a band showing that parental molecule was entirely heavy.


Why was dispersive replication not ruled out after the 1st generation culture was centrifuged in Meselon & Stahl experiment?

All strands contained a mixture of light and heavy or one new strand was made from old strand and other half was newly made.


1) How was dispersive replication ruled out of the Meselon and Stahl experiment?
2) Why?

1) 2nd generation in N14, intermediate density, sample was light and only contained N14.
2) There would always be mixture of light and heavy in every strand and only one band would form.


Describe the stages in semi-conservative replication (3)

1) Helices breaks H bonds between base pairs, DNA unwinds, 2 strands molecule separate.
2) DNA polymerase catalyses condensation reaction between 5' phosphate group of free nucleotide to the 3' OH on growing DNA chain.
3) Each chain acts as template and free nucleotides join to complementary bases.


What does the enzyme DNA polymerase need for DNA replication?

Single stranded DNA (template), 4 nucleotides, ATP.



Section of DNA on a chromosome which codes for one polypeptide.


1) How many bases code for one amino acid?
2) How many amino acids are needed in DNA?

1) 3
2) 20


State 5 characteristics of the genetic code.

1) Triplet code
2) Degenerate - more than 1 triple can encode each amino acid
3) Punctuated - stop codon
4) Universal - same triplet codes for same amino acids
5) Non-overlapping - Each base occurs in only one triplet.



Non-coding nucleotide sequence in DNA and pre-mRNA that is removed from pre-mRNA to produce mature mRNA.



Coding region in the nucleotide sequence of DNA and pre-mRNA that remains present in the final mature mRNA, after the introns have been removed.


1) Why does pre-mRNA have to be cut down?
2) How are the introns cut out of the pre-mRNA?
3) What type of cell does this occur in?

1) Longer then final mRNA so sequences of bases need to be removed.
2) Endonucleases and sequences left are exons with are spliced (joined together) with ligases.
3) Eukaryotes.



Strand of DNA acts as a template to direct the synthesis of a complementary sequence of RNA, with enzyme RNA polymerase.



Sequence of codons on mRNA used to assemble specific sequence of amino acids into a polypeptide chain, at the ribosomes.


1) What happens to the DNA?
2) What do the ribosomes allow?

1) Doesn't leave nucleus, acts as template for production of mRNA, carries info for protein synthesis from nucleus to cytoplasm.
2) Surface for attachment of mRNA.


Describe the process of transcription (7)

1) DNA helices breaks H bonds between bases, 2 strand to separate and unwind exposing bases.
2) RNA polymerase binds to template strand of DNA at start of sequence to be copied.
3) Free RNA nucleotides align opposite template strand.
4) Uracil and adenine, cytosine and guanine align.
5) RNA polymerase moves along DNA forming bonds that add RNA nucleotides to growing RNA strand. Results in mRNA. Behind RNA polymerase, DNA strands rewind to reform double helix.
6) RNA polymerase separates from template strand when reaches stop codon.
7) Production of transcript is complete and newly formed RNA detaches from DNA.


1) Describe initiation. What happens to tRNA?

1) Ribosome attaches to start codon at one end of mRNA molecule. 1st tRNA, with anticodon complementary to 1st codon on mRNA, attaches to ribosomes. 3 bases of anticodon (tRNA) complementary to 3 bases of codon (mRNA) with hydrogen bonds. Same for 2nd.


2) Describe elongation. What happens to the 1st tRNA? What happens to the ribosome?

2) 2 amino acids sufficiently close for ribosomal enzyme to catalyse formation of peptide bond between them:
1st tRNA leaves ribosome, leaving attachment site vacant. Returns to cytoplasm to bind to another copy of amino acid.
Ribosome moves one codon along mRNA strand.
Next tRNA binds.


Translation (ribosome moves along mRNA)
3) Describe termination. What happens to the ribosome?

3) Sequence repeats until stop codon is reached.
Ribosome - mRNA - polypeptide complex separates.



Several ribosomes bind to single mRNA strand, reading coded information at same time.


What is the order base codons?
What would the anticodon be if DNA was CAT?

DNA triplet > mRNA codon > anticodon tRNA


Amino acid activation

Energy from ATP is needed to attach amino acid to tRNA.


What lead to the one gene - one enzyme hypothesis?

Experiments on fungus Neurospora crassa 1940s - radiation damage to DNA prevented single enzyme from being made.


What lead to the one gene - one protein hypothesis?

Enzymes are a particular kind of protein.


What lead to the one gene - one polypeptide hypothesis?

Many proteins (haemoglobin) contain more than one polypeptide.


Post translational modification

Modification of a polypeptide.


What happens to polypeptides made on ribosomes?

Transported through cytoplasm to Golgi body (usually folded).


What can polypeptides be modified with? (3)

Carbohydrate - making glycoproteins
Lipid - making lipoproteins
Phosphate - making phospho-proteins