Flashcards for topic test 17/01/25
What is the role of DNA?
- To hold genetic information in all living cells.
What is the role of RNA?
- To transfer genetic information from DNA to ribosomes.
What are the 3 components of nucleic acids?
- Base
- Pentose sugar
- Phosphate
How are nucleotides joined together?
- By forming a bond between the phosphate group of one nucleotide and the pentose sugar of another nucleotide. (Phosphodiester bond)
How are 2 DNA polynucleotides joined together?
- Hydrogen bonding between complementary base pairs.
What are the complementary DNA bases and how many H bonds do they contain?
- Adenine and Thymine (2 H bonds)
- Cytosine and Guanine (3 H bonds)
How do DNA strands form a double helix?
- By moving in antiparallel direction and twisting around each other.
What are 3 ways the DNA structure relates to its function?
1) The DNA molecule is very large so holds lots of genetic information.
2) 2 DNA polynucleotides are held together by weak hydrogen bonds so are able to unwind easily during replication.
3) The base pairs are protected by the sugar-phosphate backbone, so are able to perform their function of complementary pairing efficiently.
What is the structure of RNA compared to DNA?
- Much shorter
- Single polynucleotide chain
- The base Uracil replaces the base Thymine.
Why does DNA replicate before mitosis and meiosis?
- To ensure daughter cells have the genetic information to produce proteins and enzymes.
What does the concept of semi-conservative replication mean?
- Each of the two new DNA molecules will contain an original strand and a new strand.
Why is semi-conservative replication crucial?
- Ensures genetic continuity
Outline the semi-conservative process in 4 steps..
1) DNA helicase breaks the hydrogen bonds between bases on the two strands.
2) DNA double helix begins to unzip
3) Exposed bases will pair with free nucleotides in the cytoplasm via complementary base pairing.
4) DNA polymerase will join the two strands via a condensation reaction forming phosphodiester bonds.
What is the genome and proteome?
- Genome is the complete set of genes in a cell.
- Proteome is the full range of proteins that a cell is able to produce.
What is the role of mRNA?
- To transfer genetic information from the DNA in the nucleus to the ribosome.
What is the structure of mRNA?
- Long, single polynucleotide
- Polymer of the RNA nucleotide
- Information in the form of codons that have a specific sequence which determines the amino acid sequence of the polypeptide.
What is the role of tRNA?
- transfers amino acids to the ribosomes to build proteins.
What is the structure of tRNA?
- Short, single polynucleotide strand.
- Hydrogen bonds between the specific base pairs cause the formation of a clover leaf structure.
- Information is in the form of anticodons.
- Contains an anticodon and an amino acid binding site.
What is transcription?
- The production of mRNA from DNA.
Outline the process of transcription…
- RNA polymerase binds to the start gene and unwinds the DNA, exposing its bases. (contains a DNA helicase which breaks the hydrogen bonds)
- Free RNA nucleotides join with their exposed complementary bases on the antisense strand via hydrogen bonding.
- RNA polymerase adds each nucleotide to the mRNA polynucleotide chain by forming phosphodiester bonds during a condensation reaction.
- RNA polymerase reaches a stop triplet code and detaches from DNA.
What is pre-mRNA and how is it modified?
- pre-mRNA contains introns and exons.
- Introns are non-coding regions of DNA so are removed, whilst exons are spliced together.
What is translation?
- Final production of polypeptides from the sequence of codons carried by mRNA.
What are the stages of translation?
1) Ribosome becomes attached to the start codon at one end of the mRNA.
2) tRNA molecule with an anticodon complementary to the mRNA codon attaches itself via complementary base pairing.
3) A second tRNA molecule attaches itself to the next codon in the same way.
4) the 2 amino acids attached to the tRNA molecules are joined by condensation reactions which form peptide bonds.
5) Ribosomes move along mRNA and another codon becomes available for base pairing.
6) First tRNA dissociates and leaves its amino acids behind.
7) Process of dissociation and adding is repeated until a polypeptide is formed.
8) Ribosome reaches a stop codon on the mRNA sequence. s
What are the components of ATP?
- The base, Adenine.
- 3 phosphate molecules.
- Ribose sugar
What is the term for ATP being a modified form of a nucleotide?
- A nucleotide derivative
What can be said about the phosphate bonds and energy?
- The phosphate bonds in an ATP molecule contain lots of energy.
- These bonds have a low activation energy so little energy is needed to break them.
How is ADP and inorganic phosphate combined?
- Plant and animal cells release energy from glucose during aerobic respiration.
- The energy released from glucose is used to combine ADP and an inorganic phosphate ion to form ATP.
What is the enzyme that catalyses the joining of ADP and inorganic phosphate?
- ATP synthase
How does ATP provide energy to a cell?
- ATP diffuses to the parts of the cell that require energy.
- ATP is hydrolysed into ADP and inorganic phosphate.
- Energy released can be used directly.
- The inorganic phosphate can be added to another compound to make it more reactive, called phosphorylation.
What enzyme catalyses the hydrolysis of ATP into ADP and Pi?
- ATP hydrolase
Describe ATP as an energy source?
- Immediate energy source rather than long term due to phosphate bonds being relatively unstable.
- ATP releases energy in smaller, more manageable quantities compared to glucose.
- ATP cannot be stored.
