section 3- nucleotides and nucleic acids

Three components of a nucleotide

• Pentose sugar (deoxyribose)

• Nitrogenous base

• A phosphate group

Sugar in DNA

Deoxyribose

Sugar in RNA

Ribose

Where is dna found?

Nucleus

Where is RNA found?

Nucleus and cytoplasm

Antiparallel

Creates the double helix shape

Bonds formed in DNA

Phosphodiester bonds

Hydrogen bonds in bases

2 AT

3 GC

What way does DNA polymerase catalyse the bases?

5’ to 3’

Four bases in DNA

• Thymine

• Adenine

• Cytosine

• Guanine

Pyrimidines

Single carbon ring

Thymine and cytosine

Purines

2 carbon rings

Adenine and guanine

DNA helicase

Breaks the hydrogen bonds between 2 DNA strands

DNA polymerase

Makes the phosphodiester bonds with new bases

DNA ligase

Okazaki fragment made from lagging strand → from the phosphodiester bonds in the sugar phosphate backbone

DNA gyrase

Unwind the double helix

Semi conservative replication

DNA Gyrase→ DNA helicase→ DNA polymerase→ DNA ligase

Results of semi conservative replication

2 identical strands of DNA, containing one original strand and one new strand of DNA

Splicing

Modifies the pre-mRNA before it is translated

Exons

Exons are joined together to make mature mRNA and leave the nucleus to be translated

Sequences can vary to create different proteins from the same gene

Introns

Stay in the nucleus

Melson and stahl experiment

Grew bacteria in heavy nitrogen (15N) and then switched to (14N)

Results of Meselon and stahl experiment

After DNA replication, the resulting molecules showed one heavy and one light strand, confirming that each DNA strand serves as a template for a new one

Transcription

Genes are translated by RNA polymerase which makes pre-mRNA by copying the template strand on the DNA→ mRNA is made because DNA is too big to leave the nucleus

mRNA leaves through nucleus pores

Gene

Section of DNA that codes for a protein

Two types of strand in transcription

• Coding/sense strand

• Template/antisense strand

What enzyme is responsible for transcription

DNA polymerase

What does transcription make?

Messenger RNA (mRNA)

Translation

1. mRNA attaches itself to a ribosome and transfer RNA molecules carry amino acids to the ribosomes

2. a tRNA molecule, with an anticodon that’s complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing

3. A second tRNA molecule attaches itself to the next codon on the mRNA in the same way

4. Ribosomal RNA(rRNA) in the ribosomes catalyses the formation of a peptide bond between the two amino acids attached to the tRNA molecules. This joins the amino acids together. The first tRNA molecule moves away, leaving its amino acid behind

5. A third tRNA molecules binds to the next codon of the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away

6. This process, continues producing a chain of linked amino acids until there’s a stop codon on the mRNA molecule

7. The polypeptide chain moves away from the ribosome and translation is complete

Universal

All organisms use the same nitrogenous bases

Non-overlapping

Codons are read three at a time

Degenerate

There are multiple codons for the same amino acid

Phosphorylate nuelcotides

Add one or more phosphate groups

ADP structure

Adenosine diphosphate

Adenine, sugar ribose and two phosphate groups

ATP structure

Adenosine triphosphate

Adenine, ribose sugar and three phosphate groups

ATP→ ADP

Hydrolysis

Remove a phosphate→ breaks covalent bond between phosphate 2+3

Energy from hydrolysis of ATP→ ADP used for

Cell signaling, active transport, cilia movement, muscle contraction, amino acid added in transcription

ADP→ ATP

Condensation reaction

Add in a phosphate and remove water

Energy from ADP→ATP used for

Respiration, fermentation, photosynthesis

Properties of ATP

Very small (easy to transport), water soluble( most reactions occur in solution so is available), easily regenerated(more ATO can be made from ADP or AMP), releases energy in small quantities (energy is not wasted)

What base is different in RNA

Uracil instead of thymine

Similarities between dna replication and transcription

• Both have template strand

• Both use DNA polymerase

• Hydrogen bonds

• Helicase enzymes

• Complementary base pairings

• DNA unwinds and Unzips

Differences between DNA replication and transcription

• Transcription creates mRNA- replication creates new complementary strand

• Transcription only small section of DNA-genes

• Different helicase enzymes

• mRNA leaves nucleus

• Transcription- uracil instead of thymine

How are the two polynucleotide chains held together

• Hydrogen bonds between base pairings

• Purine to pyridine

• A-T two H bonds

• C-G three H bonds

Explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands

• Nucleotides joined by phosphodiester bonds

• Hydrogen bonds between complementary bases

• Polynucleotide are antiparrallel to create double-helix shape