Nucleotides and Nucleic Acids OCR Biology

What is a nucleic acid?

Two types including DNA and RNA. Vital molecules as carry genetic code in all living things. Contain hydrogen, oxygen, carbon, nitrogen and a phosphate.

What is a Nucleotide?

• Monomers that make up DNA and RNA

• Biological molecules that participate in almost all biochemical processes

• Help regulate metabolic pathways

• May be components of coenzymes

What is the structure of a nucleotide?

• Made from a pentose sugar (5 carbons), organic nitrogenous base and a phosphate group

• Contain C,H,O,N and phosphate

DNA Nucleotide

• Contain Pentose sugar called deoxyribose.

• Same phosphate group but can have different base

• Adenine, thymine, Cytosine, Guanine

• DNA molecules have two polypeptide chains joined together made of lots of nucleotides

RNA Nucleotide

• Contain pentose sugar called ribose

• Has phosphate group and one of four bases- uracil replaces thymine

• Single polypeptide chain.

What is a Purine?

A type of base including Adenine and Guanine. Contain a double carbon ring structure

What is a Pyrimidine?

A type of base including Thymine, Cytosine and Uracil. Contains a single ring carbon structure.

Why do we need energy? (3)

Synthesis, Transport , Movement

What is ATP?

• Universal energy currency

• Contains adenine, ribose sugar and three phosphate groups

• Relatively unstable and cannot be stored long term

• Energy stored in fats are broken down during cellular respiration to make ATP

What are the properties of ATP?

Small, Water soluble, Contains bonds between phosphates with intermediate energy, releases energy in small quantities, Easily regenerated

What is ADP?

Adenosine diphosphate, a nucleotide composed of adenine, ribose sugar, and two phosphate groups. It is formed when ATP loses one phosphate group, releasing energy.

What is the polynucleotide structure?

A polynucleotide structure consists of a long chain of nucleotides linked by phosphodiester bonds, forming the backbone of nucleic acids like DNA and RNA.

What is the DNA structure?

Two antiparallel polynucleotide strands joined together by hydrogen bonds in complementary base pairings to make a double helix structure with sugar phosphate backbone.

Why does DNA need to replicate?

Make new cells for growth and repair, pass genetic information through reproduction

What enzymes are involved in DNA replication?

Helicase- breaks hydrogen bonds between nitrogenous bases.

DNA Polymerase- catalyzes formation of DNA from activated deoxyribose nucleotides using single stranded DNA as template

Process of DNA replication

1. Helicase causes two strands of DNA to split apart by breaking hydrogen bonds

2. Each original strand acts as template for free-floating DNA nucleotides to join to exposed bases

3. Nucleotides on new strand are joined by DNA polymerase forming sugar phosphate backbone with hydrogen bonds forming between original and new strand.

4. The strands twist to form the double helix structure with one new strand and one original strand of DNA.

Accuracy of DNA replication

Usually accurate but sometimes spontaneous mutations occur which can cause changes in DNA bases which can alter amino acid sequences and therefore protein structures

What is a gene?

Sequence of nucleotides that code for a polypeptide. This contains a sequence of amino acids that determine the order of bases in a gene and therefore a protein structure.

What is RNA?

Single polynucleotide strand containing uracil which pairs with adenine during protein synthesis.

What is mRNA?

Single polynucleotide strand made in nucleus during transcription. Carries genetic code from DNA in nucleus to cytoplasm and is used to make a protein in translation.

What is tRNA?

Single polynucleotide strand folded into clover shape. Hydrogen bonds between base pairs to hold shape. contain specific sequence of three bases called anticodon. Also have an amino acid binding site. Found in cytoplasm and involved in translation.

What is rRNA?

Form two subunits of ribosome with a protein and moves along mRNA during protein synthesis. Helps catalyse formation of peptide bind between amino acids.

Process of Transcription

1. RNA attaches to the DNA

2. Complementary mRNA is formed

3. RNA polymerase moves down DNA strand

4. mRNA leaves nucleus when RNA polymerase reaches stop codon.

5. mRNA attaches to a ribosome in cytoplasm

Process of translation

1. mRNA attaches itself to ribosome and tRNA molecules carry amino acids to the ribosome.

2. A tRNA with a complementary anticodon to the mRNA start codon by complementary base pairings, then another tRNA molecule attaches itself to the next codon in the same way.

3. rRNA in ribosome catalyse formation of peptide bond between the amino acids attached to tRNA joining the amino acids together.

4. First tRNA moves away leaving amino acid behind

5. Third tRNA molecule binds to mRNA and its amino acid binds to the first two allowing second tRNA molecule to move away

6. Pattern continues until stop codon on mRNA then the polypeptide chain (protein) moves away.