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OCR A-level Biology Module 2: Foundations in Biology > DNA and Nucleic Acids > Flashcards

DNA and Nucleic Acids Flashcards

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1
Q

What really is a nucleotide?

A
  • This is a molecule containing a 5 carbon pentose sugar. a nitrogenous base and a phosphate group!
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2
Q

How can we group the 4 bases that we have?

A
  1. THYMINE and CYTOSINE: These are pyramidines with a single ring structure
  2. ADENINE and GUAMINE: These are purines with a double ring structure!
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3
Q

How do pyramidines and purines bond together?

A
  • as they will bond via complementary base pairing, a PYRAMIDINE will always bons to a PURINE!
  • Hence, Adenine bonds to Thymine, and Cytosine bonds to Guamine!
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4
Q

What is DNA?

A
  • This is a hereditary macromolecule in cells of ALL living organisms, with the role of stroing genetic information, instructions for protien manufacture and growth for entire organism
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5
Q

What can complementary base pairing bring to DNA?

A
  • This will bring EQUAL SIZED RUNGS on DNA DOUBLE HELIX SHAPE!!!
  • This will also brong molecular stability and base-information protection for such a large macromolecule…
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6
Q

Give the 4 main differences between DNA and RNA

A

1. D = Double stranded sugar-phosphate backbone
R = Single-stranded
2. D = Made of deoxyribose
R = Made of ribose
3. D = Extremely long molecule#
R = relitavly short molecule
4. D = Found in chromosomes
R = Found in the cytoplasm

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7
Q

What is the anti-parralel structure in DNA?

and give the number of HYDROGEN BONDS FOR EACH BOND!!

A
  • This is when complementary bas pairing occurs between purines and pyramidines
  • Can be unzipped via RNA Polymerase!

***2 HYDROGEN BONDS = Aden

3 HYDROGEN BONDS = Cytosine and Guanine
2 HYDROGEN BONDS = Adenine and Thymine

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8
Q

What are the Phosphodiester Bonds?

A
  • These are the bonds that form between a A SINGLE PHOSPHATE GROUP bonded to 2 PENTOSE SUGAR GROUPS of the neighbouring nucleotide

Like with literally all biological molecules, a CONDENSATION REACTION and with HYDROLYSIS to break apart….

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9
Q

Where in the nucleotide does the Phosphodiester bond form?

*

A
  • This will form at carbon 3 and carbon 5 at the pentose sugar molecules!
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10
Q

What is the difference between ribose and deoxyribose???

A
  1. RIBOSE: Will contain URACIL over THYMINE in its structure
    Will also contain 2 hydroxyl groups in molecule
  2. DEOXYRIBOSE: Will be the normall bases that it contains, but with having only 1 hydroxyl group in molecule
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11
Q

How can we describe the direction of bonding in a DNA molecule?

A
  1. This will occur from the 3’ to the 5’
  2. This will stands for the number on the carbon atoms in the pentose sugar.
  3. Thid will mean the opposing sides of the nucleotides wil be of reverse of each other (like a mirror image)
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12
Q

How is DNA organised in Eukaryotic Cells?

A
  1. Each molecule of DNA is tightly wound around a histone protien, forming chomosomes!
  2. Hence, each chromosome = 1 DNA Molecule!
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13
Q

How is DNA organised in Prokaryotic Cells?

A
  • DNA loop is free floating in the cytoplasm, not enclosed in a membrane-bound nucleus?
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14
Q

Why are the hydrogen bonds inportant in DNA?

A

THIS ALLOWS THE MOLECULE TO BE UNZIPPED BY RNA POLYMERASE FOR DNA TRANSRIPTION and REPLICATION!!!!!!

instead of bieng held in a very rigid, bond-like structure e.g. : COVALENT or IONIC………..

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15
Q

What are the first 4 stages of DNA Replication?

A
  1. DNA double helix will unwind, via the enzyme Gyrase
  2. Double helix will unzip, via DNA Helicase, breaking hydrogen bonds and exposing bases
  3. Free phosphorylated nucleotides will bind to said exposed bases, via DNA Polymerasein 5’ > 3’ direction.
  4. For the Lagging Strand, Polymerase will add nucleotides in Okazaki Fragments, and uses PRIMERS as a location molecule
  5. For Leading Strand, nucleotides normally in 5’ > 3’ direction!!
  6. These phosphorylated nucleotides are only held via Hydrogen Bonds, at this stage….!
  7. Both strands will act as a template strand
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16
Q

What are the stages of DNA Replication following template stranding…?

A
  1. Hydrolysis of phosphorylated nucleotides will supply the energy needed to form Phosphodiester Bonding!
  2. DNA Polymerase will move down molecule in 5’ to 3’ direction
  3. As DNA Polymerase can only move in the 5’ to 3’ direction, this will mean for opposite strand, Polymerase will catalyse Phosphodiester bonds in specific chunks down the molecule

chunks = Okazaki Fragments!!

17
Q

What are the last stages of DNA Replication?????

A
  1. Once-Free phosphorylated nucleotides will now have phosphodiester bonds with neighbouring nucleotides
  2. This will mean that these nucleotides will loose 2 phopsphate groups!!
  3. Hydrogen bonding will now form between complamentary base pairs!
  4. 2 new GENETICALLY IDENTICAL DNA strands are now made, in a process of SEMI-CONSERVATIVE replication!
18
Q

Difference between activated and normall nucleotides?

A
  • ACTIVATED = 3 phosphate groups per nucelotide, whilst rest of molecule remains the same
  • NORMALL = The regular single phosphate group per nucleotide..
19
Q

Why do have Activated and Normall Nucleotides

A
  1. Because during condensation, phosphodiester bonds will have to form during semi-conservative replication
  2. This will mean that loosing the 2 additional phosphate groups will allow for MASSIVE ENERGY RELEASE to form the PHOSPHODIESTER BONDS in the first place!!!
20
Q

How may a DNA mutation occur?

and name this mutation….

A
  1. An incorrect nucleotide may be inserted as a wrong sequence in the sequence
  2. This will change the genetic code!!

this is a POINT MUTATION, and MUST BE KNOWN….

21
Q

How can such mutations be prevented during the Cell Cycle?

A
  • Negative regulator protiens (P53 Suppressor Protiens….) can undergo certain checkpoints during cycle!
  • Is needed, cell can be moved into G0 State, and if unfixable, apoptosis…!!!, preventing replication of the same genetically defective cell
22
Q

What can result from mutation in DNA Sequence?

A

CANCER CELLS!!

Cells gone rogue, dividing uncontrollably, forming tumour all throughout the body….

23
Q

What substance can we use to break Nuclear Envelope to extract DNA?

A
  1. Use a DETERGENT!
  2. This will attract both phospholipid and water molecules in bilayer
  3. Hence, nuclear envelop will break away..

DETERGENT = AMPHIPHILIC MOLECULE!

24
Q

Differences between ATP and Nucleotides!

A
  1. ATP = Ribose replaced by Dexoyribose
  2. OH- Group an its carbon 2
    Nucleotides = Will both have pentose sugar, phosphodiester bonds ect………..
25
Q

Difference between Ribose and Deoxyribose?

A
  1. RIBOSE = 2 HYDROXYL GROUPS PER PENTOSE
  2. DEOXYRINOSE = 1 HYDROXYL GROUP PER PENTOSE
26
Q

Name and describe the experiment proving semi-conservative replication!

BE SURE TO ONLY DESCRIBE HERE, anothe flashcard will allow explanations later on….

A

MESELSON - STAHL EXPERIMENT!!
1. Here, E.Coli was initially grown in growth medium of N-15, where DNA used it to fix into nucleotide manufacture! (giving entire molecule N-15 based)
2. This batch was then allowed to grow in a N-14 medium, using the surrounding N-14 to also use in nucleotides
3. Batch again replicated its DNA in N-14 medium, proving its semi-conservative nature!

Heavy nitrogen = N-15
Light Nitrogen = N-14

27
Q

How did the Meselson-Stahl Experiment prove the nature of semi-conservative replication???

A
  1. At each stage of heavy/light nitrogen growth generation, DNA was extracted , placed in a solution and was CENTRIFUGED
  2. Here, DNA bands of different depths and densities can be observed!
  3. First Gen = N-15 = low-depth, 100% band
  4. 2nd Gen = N-15 + N-14 = mid-depth, 100% intermediate band
  5. 3rd Gen = N-14 + (N14+N-15) = **high and mid-depth, 100% N-14 and intermediate band **

INTERMEDIATE BAND = 50% N-14 and 50% N-15!!

28
Q

What would a Meselson-Stahl Experiment of conservative and dispersed look like?

A
  1. CONSERVATIVE = 2 distinct bands of 100% N-14 and N-15, at higher and lower depths = whole molecule acting as a template, with a brand-new DNA molecule
  2. DISPERSED = 1 single band as a mixture of N-14 and N-15 at mid-ranging depths = mixture of original and new nucleotides to nitrogens used!
29
Q

List and Explain the 3 types of RNA!!!

A
  1. mRNA = Transribed from DNA, carries message base sequence to ribossomes
  2. tRNA = Fork-shaped molecule, bringing amino acids to ribossomes at “Division of Labour”
  3. rRNA = made in the nucleolus, forming majority mass of ribossomes
30
Q

How can we calculate the number of base combinations to form amino acids!

A
  • One base can have 4 possible amino acids to form
  • Therefore, as 3 bases will code for 1 amino acid: 444 = 64 possible amino acid combinations!!
31
Q

Why can we describe the nature of genetic code being degenerate?

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A
  • Consists of 1 start and 3 stop codons!
  • This will mean that each possible amino acid will have 3 possible codons
  • Hence, minimising risk of point mutations, as a mino change in codon base cam still code for the same amino acid as original!!

hence, last base can change, coding for the same amino acid…

32
Q

Whay can we describe the nature of genetic code being non-overlapping?

A
  • The triplet codons are all discrete to one another, with no overlapping of bases whatsoever! (bases do not go on to code for part of subsequent bases)
  • Beneficial, mutation affecting one base will only affect that one base instead of affecting the subsequent 3 bases = massive change to ammino acid coding
33
Q

Whay can we describe the nature of genetic code being universal?

A
  • Because in (nearly) all living organisms, the same triplet codons will code for the same amino acids!!
34
Q

What are the stages of DNA Transcription?

A
  1. DNA Helicase will break hydrogen bonding between complamentary base pairs (anti-parralel)
  2. Free phosphorylated nucleotides will form new hydrogen bonds with said exposed bases
  3. RNA Polymerase catalyses phosphodiester bonds between “free” nucleotides (until end of gene)
  4. mRNA now produced, THYMINE = URACIL
  5. mRNA leaves nucleus via nuclear pores!
35
Q

What are the stages of DNA Translation?

A
  1. mRNA will now bind to the ribossomes, starting with start codon
  2. tRNA with anticodon complamentary to start codon will hydrogen bond
  3. PROCESS CONTINUES, where tRNA carries corresponding amino acids allows peptide bonds to form, via Peptyl Transferase (proximity!!)
  4. Polypeptides now formed, requiring ATP Energy to do so
  5. Polypeptides transported via vesicles (see Div of Lab)
36
Q

Describe meaning of Template and Coding Strand!

A
  1. Template: Strand of DNA that serves as a literal template during Transription (RNA making…)
  2. Coding: DNA strand whose base sequence literally matches that of mRNA (that “above” stand), but mRNA = URACIL

mRNA is a copy of the coding strand, but initially made using the template strand (due to the “complamentarty/anit-parralel nature)

37
Q

What takes place at the end of translation?

A
  1. At the stop codon, the ribossomes will detach, but a “train” of ribossomes may be evident = Large + Rapid amounts of polypeptides produced as result
  2. The new polypeptide will eventually fold into specific 3D Tertairy structure to carry out correct, specific function
38
Q

How can we describe tRNA’s molecular shape?

A
  1. This is a clover/fork shaped molecule
  2. Contains an anticodon sequence on the base, with unpaired bases in both sides on “arms”
  3. The very top has an amino acid site of attachement (how amino acids are brought to the ribossome in the first place)

bbtw has its own base pairing in and throughout the molecule.. . . .

39
Q
A

OCR A-level Biology Module 2: Foundations in Biology (6 decks)

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