BIOLOGY - AS Level - 2.3 - Nucleic Acids

What are nucleotides?

Monomers of nucleic acids.

What is the structure of a nucleotide?

• A Penrose sugar

• A Nitrogenous base

• A Phosphate group

What is a polynucleotide?

A chain of nucleotides bonded together via condensation reactions.

What bonds are between nucleotides?

Phosphodiester bonds.

What are Phosphodiester bonds?

Strong covalent bonds formed between the phosphate group of one nucleotide and the sugar of another.

What are the purines?

Adenine and Guanine

What are the pyrimidines?

Thymine (DNA) or Uracil (RNA) and Cytosine

What are the four bases for DNA?

• Adenine

• Guanine

• Cytosine

• Thymine

What is the difference between purines and pyrimidines?

Purines contain a two carbon ring structure.

Pyrimidines contain a one carbon ring structure.

What are the complimentary base pairs?

Adenine pairs with Thymine/ Uracil.

Cytosine pairs with Guanine.

What bonds are between complimentary bases?

Hydrogen bonds

• 2 between Adenine and Thymine/Uracil.

• 3 between Cytosine and Guanine.

What is DNA?

A type of a nucleic acid which contains the instructions needed to make proteins.

What does DNA stand for?

Deoxyribonucleic acid.

What is the structure of a DNA nucleotide?

• Deoxyribose – pentose sugar

• Adenine, Thymine, Cytosine and Guanine base

• A phosphate group

What is the structure of DNA?

2 polynucleotide chains in double helix.

What are the features of DNA?

• Sugar-phosphate backbone- this protects coding bases on the inside of the helix

• Double stranded – this allows strands to act as a template in DNA replication

• Large molecule – it stores lots of information

• Double helix- makes a molecule compact

• Complimentary based pairing- this allows accurate DNA replication

• Weak hydrogen bonds- this allows strands to separate in DNA replication

What is RNA?

A type of nucleic acid that uses information from DNA to synthesise proteins.

What is the structure of an RNA nucleotide?

• Ribose – a pentose sugar

• Adenine, Uracil, Guanine, or cytosine base

• A phosphate group

What is the structure of an RNA molecule?

Short single stranded helix

What are the three forms of RNA?

• Messenger RNA (mRNA)

• Transfer RNA (tRNA)

• Ribosomal RNA (rRNA)

What is the differences between DNA and RNA?

• The sugar molecule in a RNA nucleotide is ribose whereas the sugar molecule in a DNA nucleotide is deoxyribose

• RNA has the nitrogenous base uracil instead of thymine in DNA

• An RNA chain is usually single stranded whilst a DNA is usually double stranded

• RNA is shorter whilst DNA is longer

• What type of replication is used when replicating DNA?

Semi-conservative replication

• This results in two new molecules each in which contains one of strand and one new strand.

What is the DNA replication process?

1. DNA unwinds using the enzyme DNA gyrase

2. DNA unzips using the enzyme DNA helicase, which breaks the hydrogen bonds between the bases

3. Free nucleotides attached to expose bases, with complementary base pairing

4. The new nucleotide bases are attached with the enzyme DNA polymerase

5. The two strands are joined with the enzyme DNA ligase

What does the enzyme DNA gyrase do?

Unwinds the DNA strand.

What does the enzyme DNA helicase do?

Unzips the DNA strand.

What does the enzyme DNA polymerase do?

Catalyse the addition of new nucleotide bases using the original single strand template.

What does the enzyme DNA ligase do?

Catalyse the synthesis of the lagging strand.

What is DNA condensed into?

Chromosomes

What is a gene?

A part of DNA that codes for a polypeptide.

what is a locus?

The position of a gene on a chromosome.

What is a genome?

A complete set of genes.

What is a proteonome?

The full range proteins that sell as capable of producing.

What is the genetic code?

The sequence of bases that code for amino acids.

Why is DNA condense into chromosomes?

DNA is very long and must be totally packed up to fit in the nucleus of a eukaryotic cell.

How is DNA condensed into chromosomes?

• DNA molecules are wound around proteins known as histones to form a DNA histone complex.

• These complexes coil further to form chromatin which helps pack the DNA into chromosomes.

What are the three features of the genetic code?

• Universal – each DNA triplet codes for the same amino acid in all organisms

• Non-overlapping– it is red starting from a fixed point in groups of three bases.

• Degenerate – most amino acids are coded for by more than one triplet.

What is mRNA?

A type of RNA synthesis during the process of transcription.

What is the role of mRNA?

To carry genetic information from the DNA in the nucleus to the ribosomes.

What are the features of mRNA?

• Single stranded molecule

• Contains a base sequence complementary to a DNA sequence

• Contains codons

• Small

What are codons?

A set of three bases that code for an amino acid.

What is tRNA?

A type of RNA used in the process of translation.

What is the role of tRNA?

To transport amino acids to ribosomes to build up a polypeptide chain.

What are the features of tRNA?

• Single stranded molecule folded into a clover shape

• Uses hydrogen bonds between complimentary base pairs to hold its shape

• Contains an anticodon at one end

• Contains an amino acid binding site at the opposite end

What is rRNA?

It combines with other proteins to form ribosomes.

What is the role of rRNA?

rRNA is responsible for catalysing the peptide bonds that form during translation.

What are the two processes involved in protein synthesis?

Transcription and translation

Which process goes first in protein synthesis ?

Transcription goes first, then translation.

What is the process of transcription?

• The enzyme RNA polymerase binds to DNA

• The enzyme breaks the hydrogen bonds between the complementary DNA bases and the two strands of the double helix separates

• Free RNA nucleotides align with the DNA template strand through complimentary base pairing

• RNA polymerase catalyse the formation of phosphodiester bonds between the adjacent RNA nucleotides

• Complementary mRNA strand is formed and detaches from the DNA strand

• The mRNA strand passes out of the nucleus, through the nuclear pores, and attaches to a ribosome

What is the process of translation?

• A ribosome binds to the mRNA strand at a start codon

• A tRNA molecule carrying an amino acid and an anticodon that is complimentary to the start codon binds to the mRNA

• A second tRNA molecule with an amino acid and an anticodon complementary to the next mRNA codon attach it to the mRNA strand

• These tRNA molecules are held in place with temporary hydrogen bonds between the complimentary bases

• The amino acids carried by the first two tRNA molecules are bonded together with peptide bonds via a condensation reaction

• The first tRNA molecule detaches from the mRNA strand

• This process is repeated, lengthening the polypeptide chain

• The sequence continues until the ribosome reaches a stop codon on the mRNA strand

• The completed polypeptide chain attaches from the ribosome and can fulfil its use

What are codons?

A set of three bases on mRNA that codes for an amino acid.

What are anticodons?

A set a three bases that are complimentary to a codon on mRNA.

What is rRNA?

Ribosomal RNA

What is the role of rRNA?

Catalysing the peptide bonds that form during translation.