NUCLEOTIDES AND NUCLEIC ACIDS

FOUNDATIONS IN BIO

What type of bond is a phosphodiester bond?

A covalent bond

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

What elements do all nucleotides contain?

CHONP

What is the structure of a nucleotide?

• Pentose sugar

• Phosphate group

• Nitrogenous base

Name the pentose sugars in DNA & RNA.

DNA: deoxyribose

RNA: ribose

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

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

Name the purine bases

• Adenine

• Guanine

two-ring molecules

Name the pyrimidine bases

• Cytosine

• Thymine or Uracil (in RNA)

Name the complementary base pairs in DNA

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

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

Name the complementary base pairs in RNA

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

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

Why is DNA replication described as semiconservative?

* Strands from original DNA molecule act as templates.

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

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

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

Identify features of the genetic code

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

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

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

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

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

What does transcription produce and where does it occur?

• Produces mRNA

• Occurs in nucleus

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

What does translation produce and where does it occur?

• Produces proteins

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

Describe the structure of adenosine triphosphate (ATP)

• Has a pentose sugar Ribose

• Has a nitrogenous base Adenine

• Has 3 inorganic phosphate groups

Describe the structure of adenosine diphosphate (ADP).

\- nucleotide derivative of adenine

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\- has a pentose sugar (Ribose)

\- has a nitrogenous base ( adenine)

\- has 2 inorganic phosphate groups

What is a mutation?

* An alteration to the DNA base sequence.

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* Mutations often arise spontaneously during DNA replication

What bond is formed between nucleotides?

Phosphodiester bond

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

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

What is rRNA?

• ribosomal RNA

• Its found in the ribosome

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

DNA

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

What is RNA?

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

What are Purines?

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

- adenine and guanine.

Pyrimidines

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

- cytosine and thymine (Uracil)

ATP

Adenosine triphosphate

Provides energy for chemical reactions in the cell

What is a Polynucleotide?

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

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

DNA helicase

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

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

Gene

A sequence of DNA nucleotides that codes for a polypeptide

Triplet

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

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

What is an anticodon?

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

Stop codon

codon that signals to ribosomes to stop translation

What is DNA polymerase?

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

Exons

sections of DNA that code for amino acid sequences.

What is RNA polymerase?

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

DNA topoisomerase

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

DNA primase

places a primer to tell DNA polymerase to stop working

DNA ligase

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

enzymes needed for DNA replication

DNA topoisomerase

DNA helicase

DNA primase

DNA polymerase

DNA ligase

What enzymes are needed for transcription?

Helicase

RNA polymerase

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

hydrogen bonding between complementary base pairs on two antiparallel DNA polynucleotides

Which direction is the gene strand always read in?

5’ to 3’