Chapter 5 - Nucleic acids and their functions Flashcards
What are the 3 components of a nucleotide?
A phosphate group.
A pentose sugar.
An organic (nitrogenous) base.
What are the two groups of organic bases and what bases are in these groups?
Pyridamines - Uracil, Thymine and Cytosine.
Purines - Adenine and Guanine.
What is the molecule that makes energy available when it is needed?
ATP - Adenosine Triphosphate.
What is the structure of ATP?
It is a nucleotide so it contains the base Adenine, the sugar ribose and 3 phosphate groups.
What is the ATP molecule hydrolysed into when energy is needed?
Adenosine Diphosphate and an inorganic phosphate ion.
What is the addition of phosphate to ADP called?
Phosphorylation.
What are the advantages to using ATP as an intermediate instead of glucose directly?
- ATP to ADP involves a single reaction that releases energy immediately.
- Only one enzyme is needed to release energy from ATP.
- ATP releases energy in small amounts, when and where it’s needed.
- It provides a common source of energy for many different chemical reactions.
What processes does ATP provide energy for?
- Metabolic processes - to build large complex molecules.
- Active transport - Allow molecules to be moves against a concentration gradient.
- Movement - muscle contraction.
- Nerve transmission.
- Secretion - packaging and transport.
What is the structure of DNA?
Two polynucleotide strands wound around each other in a double helix. Sugar-phosphate backbone running anti-parallel to each other.
What are the 4 bases in DNA and which is complementary to which? What holds the bases together?
Adenine, Thymine, Guanine and Cytosine.
Adenine pairs with Thymine and Cytosine pairs with Guanine.
Hydrogen bonds hold them together C-G has 3 and A-T has 2.
How is DNA suited to its functions?
- Very stable molecule and its information passes essentially unchanged between generations.
- Very large so carries a large amount of genetic information.
- Two strands are easily separated.
- The sugar-phosphate backbone protects the genetic information.
What is the structure of RNA?
- A single stranded polynucleotide.
- Contains the pentose sugar ribose.
- Contains Cytosine, Adenine, Guanine but Uracil instead of Thymine.
What are the 3 types of RNA involved in the process of protein synthesis?
Messenger RNA.
Ribosomal RNA.
Transfer RNA.
Who proposed the molecular structure of DNA ?
Watson and Crick.
What are the 2 main roles of DNA?
Replication and Protein synthesis.
What were the 3 possibilities thought of for the replication of DNA?
Conservative replication.
Semi-conservative replication.
Dispersive replication.
What is the Meselson-Stahl experiment?
- Culture E. Coli. in 15N until it was incorporated into their DNA.
- Then washed, and transferred into 14N and allowed to divide for one generation.
- This was then centrifuged and this had a mid point density which ruled out conservative replication.
- Allowed to divide once more and then centrifuged again, proved theory of Semi-conservative as it settled at mid point and high point in the tube.
How many bases code for an amino acid?
3 (Triplet code).
Why does the RNA need to be processed before it can be used to synthesised the polypeptide?
Because it contains sequences of bases that have to be removed (Introns).
What is an exon?
Nucleotide sequence in DNA and pre-mRNA that remains present in the final mature mRNA , after introns have been removed.
What is the process of protein synthesis?
- DNA.
- Transcription in the nucleus.
- mRNA.
- Translation at ribosomes.
- Polypeptide.
What is the difference between Transcription and Translation?
Transcription - One strand of DNA acts as a template for the production of mRNA.
Translation - mRNA acts of a template to which tRNA molecules attach, and the amino acids they carry are linked to form a polypeptide.
What are the 3 enzymes involved in ‘unzipping’ DNA?
- DNA helicase; breaks the hydrogen bonds between the bases.
- DNA Polymerase.
- DNA Ligase.
What are the steps in Transcription?
- DNA helicase breaks the H bonds between bases.
- RNA Polymerase binds to the beginning of the template strand.
- Free nucleotides align opposite the template strand.
- RNA Polymerase moves along and forms bonds adding RNA nucleotides.
- Polymerase separates from the template strand when ‘Stop’ signal is reached.
What are the steps in Translation?
- A ribosome attaches to a ‘Start’ codon.
- A tRNA with a complementary anticodon attaches to the ribosome.
- Another tRNA attaches to the other attachment site.
- The two amino acids are close enough for a ribosomal enzyme to catalyse the formation of a peptide bond between them.
- The 1st tRNA leaves the ribosome and the ribosome moves one codon along.
- The next tRNA binds until a ‘Stop’ codon is reached.
