NUCLEOTIDES AND NUCLEIC ACIDS

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What type of bond is a phosphodiester bond?

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FOUNDATIONS IN BIO

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1

What type of bond is a phosphodiester bond?

A covalent bond

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2

What are some differences between a molecule of DNA and RNA?

  1. The pentose sugar in DNA is deoxyribose and in RNA is ribose. ‘

  2. RNA contains uracil instead of thymine

  3. DNA is double-stranded whereas RNA is single-stranded

  4. DNA has hydrogen bonds between the two complementary strands

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3

What elements do all nucleotides contain?

CHONP

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4

What is the structure of a nucleotide?

  • Pentose sugar

  • Phosphate group

  • Nitrogenous base

<ul><li><p>Pentose sugar </p></li><li><p>Phosphate group</p></li><li><p>Nitrogenous base</p></li></ul>
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5

Name the pentose sugars in DNA & RNA.

DNA: deoxyribose

RNA: ribose

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6

Describe how polynucleotide strands are formed and broken down.

  • Condensation reactions form strong phosphodiester bonds between a sugar of one nucleotide and the phosphate group of another (sugar-phosphate backbone).

  • Hydrolysis reactions use a molecule of water to break these bonds.

  • Enzymes catalyse these reactions

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7

Describe the structure of DNA.

  • A double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones).

  • H-bonds form between complementary base pairs (AT & GC) on the strands

  • The strands are anti parallel - They have the same sequence running in opposite directions

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8

Name the purine bases

  • Adenine

  • Guanine

two-ring molecules

<ul><li><p>Adenine </p></li><li><p>Guanine </p></li></ul><p>two-ring molecules</p>
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9

Name the pyrimidine bases

  • Cytosine

  • Thymine or Uracil (in RNA)

<ul><li><p>Cytosine</p></li><li><p>Thymine or Uracil (in RNA)</p></li></ul>
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10

Name the complementary base pairs in DNA

  • 2 H-bonds between adenine (A) + thymine (T)

  • 3 H-bonds between guanine (G) + cytosine (C)

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11

Name the complementary base pairs in RNA

  • 2 H-bonds between adenine (A) + uracil (U)

  • 3 H-bonds between guanine (G) + cytosine (C)

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12

Why is DNA replication described as semiconservative?

  • Strands from original DNA molecule act as templates.

  • New DNA molecule contains 1 old strand & 1 new strand

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13

Explain the role of DNA helicase in semiconservative replication.

Breaks H-bonds between base pairs to form 2 single strands, each of which can act as a template

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14

How is a new strand formed during semiconservative replication?

  1. DNA helicase breaks the H bonds between the 2 polynucleotide DNA strands

  2. This causes the helix to unzip and form 2 single strands

  3. Each original strand now acts as a template for a new strand

  4. Free nucleotides attach to exposed bases by complementary base pairing.

  5. DNA polymerase joins adjacent nucleotides on new strand in a 5' → 3' direction via condensation reactions to form phosphodiester bonds.

  6. H-bonds form between the bases on the original and new strand

  7. This causes it to twist into a double helix

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15

Identify features of the genetic code

  • Non-overlapping= each triplet is only read once.

  • Degenerate= more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids).

  • Universal= same bases and sequences used by all species.

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16

How does a gene determine the sequence of amino acids in a protein?

Consists of base triplets that code for a specific amino acids.

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17

What does transcription produce and where does it occur?

  • Produces mRNA

  • Occurs in nucleus

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18

What happens after a strand of mRNA is transcribed?

  • RNA polymerase detaches at terminator region.

  • H-bonds reform & DNA rewinds

  • Splicing removes introns from pre-mRNA in eukaryotic cells.

  • mRNA moves out of nucleus via nuclear pore & attaches to ribosome

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19

What does translation produce and where does it occur?

  • Produces proteins

  • Occurs in cytoplasm on ribosomes (which are made of protein + rRNA)

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20

Describe the structure of adenosine triphosphate (ATP)

  • Has a pentose sugar Ribose

  • Has a nitrogenous base Adenine

  • Has 3 inorganic phosphate groups

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21

Describe the structure of adenosine diphosphate (ADP).

- nucleotide derivative of adenine

- has a pentose sugar (Ribose)

- has a nitrogenous base ( adenine)

- has 2 inorganic phosphate groups

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22

What is a mutation?

  • An alteration to the DNA base sequence.

  • Mutations often arise spontaneously during DNA replication

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23

What bond is formed between nucleotides?

Phosphodiester bond

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24

What is mRNA?

  • Messenger RNA

  • Produced during transcription – RNA polymerase uses DNA as a template to provide mRNA strand

  • It carries the genetic code from the nucleus to the cytoplasm – provides the instructions for making a protein on the ribosome in translation

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25

What is tRNA?

  • Transfer RNA

  • Its found in the cytoplasm

  • It has an amino acid binding site at one end and an anticodon at the other

  • It carries amino acids to ribosomes

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26

What is rRNA?

  • ribosomal RNA

  • Its found in the ribosome

  • It helps catalyse the formation of peptide bonds between amino acids during translation

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27

DNA

A complex molecule containing the genetic information that makes up the chromosomes.

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28

What is RNA?

A single-stranded nucleic acid that passes along genetic messages.

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29

What are Purines?

Nitrogenous bases that have a double ring of carbon and nitrogen atoms

- adenine and guanine.

<p>Nitrogenous bases that have a double ring of carbon and nitrogen atoms</p><p></p><p>- adenine and guanine.</p>
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30

Pyrimidines

Nitrogenous bases that have a single ring of carbon and nitrogen atoms

- cytosine and thymine (Uracil)

<p>Nitrogenous bases that have a single ring of carbon and nitrogen atoms</p><p></p><p>- cytosine and thymine (Uracil)</p>
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31

ATP

Adenosine triphosphate

Provides energy for chemical reactions in the cell

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32

What is a Polynucleotide?

A polymer consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA.

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33

What is a Phosphodiester bond?

  • The type of bond that links the nucleotides in DNA or RNA.

  • It joins the phosphate group of one nucleotide to the hydroxyl group on the sugar of another nucleotide

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34

DNA helicase

- Breaks the hydrogen bonds between the two polynucleotide DNA strands.

- Unzips the double helix to form 2 single strands during DNA replication

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35

Gene

A sequence of DNA nucleotides that codes for a polypeptide

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36

Triplet

The three nucleotides of DNA which code for one amino acid.

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37

What is a Codon?

A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

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38

What is an anticodon?

A group of three bases on a tRNA molecule that are complementary to an mRNA codon

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39

Stop codon

codon that signals to ribosomes to stop translation

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40

What is DNA polymerase?

An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.

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41

Exons

sections of DNA that code for amino acid sequences.

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42

What is RNA polymerase?

An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new RNA strand.

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43

DNA topoisomerase

An enzyme that unwinds and winds coils of DNA that form during replication and transcription.

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44

DNA primase

places a primer to tell DNA polymerase to stop working

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45

DNA ligase

an enzyme that eventually joins the sugar-phosphate backbones of the Okazaki fragments

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46

enzymes needed for DNA replication

DNA topoisomerase

DNA helicase

DNA primase

DNA polymerase

DNA ligase

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47

What enzymes are needed for transcription?

Helicase

RNA polymerase

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48

What causes the formation of a double helix shape in DNA?

hydrogen bonding between complementary base pairs on two antiparallel DNA polynucleotides

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49

Which direction is the gene strand always read in?

5’ to 3’

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