B2 2.6-2.7 Flashcards

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1
Q

Nucleic Acids

A

Very large molecules constructed by linking nucleotides to form a polymer.

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2
Q

Nucleotide Structure

A
  • A pentose sugar.
  • A phosphate group (negatively charged, acidic).
  • A base- contains nitrogen.
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3
Q

How are nucleotides bonded?

A

Covalently

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4
Q

How are nucleotides made into polymer chains?

A
  • Covalent bonds form between the pentose sugar and the phosphate groups of the molecules.
  • This creates a strong backbone of alternating sugars and phosphates, with a base on each one.
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5
Q

How many types of nucleotides are there?

A

Four, one for each base.

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6
Q

How many sequences of bases are possible along a DNA molecule?

A

Literally any sequence

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7
Q

What does the base sequence do?

A

Stores information

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8
Q

What do the Phosphates and Sugars do?

A

Support the structure of the base sequence.

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9
Q

How are DNA and RNA different?

A
  • DNA has 1 less Oxygen atom.

- DNA is double stranded, RNA single stranded.

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10
Q

DNA bases vs RNA bases

A
Adenine
Cytosine
Guanine
DNA: Thymine
RNA: Uracil
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11
Q

What does DNA consist of?

A

Two strands of antiparallel covalently bonded nucleotides.

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12
Q

Why are the strands of DNA antiparallel?

A

Because they run in opposite directions to one another, one from 5’ to 3’, the other from 3’ to 5’.

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13
Q

What is a word for DNA’s structure?

A

Double Helix structure.

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14
Q

Complementary Base Pairing

A

Each specific base can only pair with one other:
Adenine + Thymine (Uracil)
Guanine + Cytosine

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15
Q

How are the strands of DNA held together?

A

By hydrogen bonds between the bases.

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16
Q

What are molecular models?

A

Current theories of the time.

They are a representation of an idea, and help to fabricate them physically.

17
Q

What was the first model for DNA structure?

A
  • First model consisted of three-stranded DNA- a triple helix with bases on the outside and magnesium holding it together with ionic bonds to the phosphate groups.
  • This was later rejected due to an inconsistency in magnesium levels.
  • It also did not consider Chargaff’s Principle (also known as the base pair rule-bases should be in a 1:1 ratio).
18
Q

What did Crick and Watson do when the first DNA structure was rejected?

A
  • They then used cardboard cut outs to realise how the different elements of DNA would fit together, creating the Double Helix structure.
  • They then prepared a second model, which ‘just looked right’.
  • This began a molecular biology revolution.
19
Q

When a cell divides…

A

… so do the strands of a double helix

20
Q

How does complementary base pairing work?

A
  • The base strand on the old strand determines that of the new strand- only nucleotides with a complementary base to the next base on the old strand can be added, e.g. Adenine to an existing Thymine base.
  • The H-Bonds in between them stabilize the structure.
21
Q

Who provided the first evidence for semi-conservative replication?

A

Meselson and Stahl in 1958- published evidence.