Nucleic Acids, Mitosis & Cancer Flashcards
What does DNA and RNA stand for?
DNA: Deoxyribonucleic acid
RNA: Ribonucleic acid
What is a nucleotide made up of?
- A pentose sugar.
- A nitrogen-containing organic base.
- A phosphate group.
How is a polynucleotide formed?
- Nucleotides join to form polynucleotide strands.
- Via condensation reactions.
- Forming phosphodiester bonds.
- Forming the sugar-phosphate backbone.
What are the components of DNA?
- Deoxyribose (the pentose sugar).
- The nitrogen containing organic base is either adenine (A), guanine (G), cytosine (C) or thymine (T). They fall into 2 groups: purines and pyrimidines. Purines are larger than pyrimidines. A and G are purines and T and C are pyrimidines.
- A phosphate group.
How is DNA structured?
Two polynucleotide strands, one running the opposite way to the other, twisting to form a double helix. The bases in each strand are held together by hydrogen bonding.
What bases are paired with each other, what term is used to describe this pairing and how many hydrogen bonds are formed between the bases?
- Adenine always pairs with thymine.
- Guanine always pairs with cytosine.
(AT GC —> At Greenhead College). - Complementary base pairing.
- 2 hydrogen bonds between adenine and thymine.
- 3 hydrogen bonds between guanine and cytosine.
How does the structure of DNA relate to its function?
- It is a stable molecule as it is a double helix and there are many hydrogen bonds.
- It is strong due to the covalent bonds in the sugar-phosphate backbone.
- Complementary base pairing allows DNA to replace itself exactly when cells divide. The weak hydrogen bonds allow strands to separate in this process.
- It is compact. DNA molecules are long, so contain large amount of coded information. However, the double helix shape allows DNA to fit inside the nucleus of the cell.
- It has a precise genetic code, determined by the sequence of bases, which controls protein synthesis.
How many bases code for one amino acid?
Three. Triplet code.
What is RNA?
- Ribonucleic acid.
- It is a relatively short, usually single stranded polynucleotide made up of RNA nucleotides.
- Contains a pentose sugar called ribose.
- Contain a nitrogenous organic base, either adenine (A), guanine (G), cytosine (C) or uracil (U).
- Contain a phosphate group.
How is DNA replicated?
Semi-conservative replication:
- DNA helicase unwinds the DNA double helix by breaking the weak hydrogen bonds between the complementary bases in polynucleotide strands.
- Both strands of DNA can now act as a template for the formation of a new strand.
- New DNA nucleotides are attached to the exposed bases and attach by complementary base pairing.
- New hydrogen bonds form between the bases.
- DNA polymerase joins the adjacent nucleotides together with phosphodiester bonds via condensation reactions.
What is the evidence for semi-conservative replication?
- Cultures of E.Coli were grown in heavy 15-nitrogen mediums and were then moved to a medium containing normal light 14-nitrogen.
- Generation 0 = DNA all heavy.
- Generation 1 = Two hybrid molecules of DNA
- Generation 2 = Two hybrid molecules and two all new light DNA (50% hybrid and 50% light)
- Generation 3 = Two hybrid molecules and six all new light DNA (25% hybrid and 75% light).
- With each successive generation, the proportions of hybrid DNA halves and all the remaining DNA is light.
What is ATP?
- The organic base is adenine.
- Contains a ribose sugar.
- Three phosphate groups.
- ATP is synthesised by the addition of ADP to an inorganic phosphate. A condensation reaction catalysed by the enzyme ATP synthase.
- ATP is easily broken by the enzyme ATP hydrolyse in a hydrolysis reaction.
Why is ATP useful?
- The breakdown is a single reaction, making energy immediately available.
- ATP is water soluble and easily moved around inside cells, but cannot pass through cell membranes.
- The breakdown of a molecule of ATP releases a small amount of energy.
What is the role of ATP?
- Active transport: required to move substances against a concentration gradient using carrier proteins in plasma membranes.
- Exocytosis: Required to make vesicles by the Golgi apparatus prior to secretion from cells.
- Synthesis of substances: Required to make large molecules from smaller ones.
- Movement: Required for muscle contraction.
- Activation of other molecules: ATP can transfer its phosphate group to other molecules, phosphorylating them and making them more reactive.
What is a chromosome?
Long, liner structures consisting of DNA and histone proteins.
What is a homologous chromosome?
A pair of chromosomes containing the same genes in the same positions (same locus), each derived originally from a different parent’s gamete at fertilisation.
What is a chromatid?
One of the two threads of a chromosome, formed after DNA replication.
What is a centromere?
Holds together 2 identical sister chromatids.
What is chromatin?
DNA and proteins together form this substance.
What is the cell cycle?
Each phase of the cycle involves specific cell activities:
- G1: cells prepare for DNA replication.
- S: DNA replication occurs.
- G2: a relatively short gap before mitosis.
- M: Mitosis.
Interphase - This is when DNA replicates, protein synthesis occurs, there is an increase in number of organelle and ATP production (respiration). This occurs in G1, S and G2 (when the cell is not in mitosis).
What does the duration of interphase tell us?
The rate of cell division. A shorter interphase means cells divide more often.
What is a duplicated chromosome?
- Two sister chromatids held together at the centromere.
- Homologous: a pair that have the same genes at the same loci.
What are the uses of mitosis?
- Growth and replacing tissue during repair.
- Asexual reproduction.
- Maintains chromosome number from one generation to the next.
What are and explain the stages of mitosis?
- Prophase:
- Chromosomes condense due to the coiling up of DNA and become visible.
- The nuclear membrane breaks down. - Metaphase:
- Chromosomes line up along the equator of the cell and each attaches to an individual spindle fibre by its centromere. - Anaphase:
- Centromere divides.
- Spindle fibres contract, pulling apart the chromatids of each chromosome.
- Sister chromatids go to opposite poles. - Telophase:
- Chromosomes uncoil and become threadlike again.
- No longer visible.
- New nuclear membrane forms around the chromosomes. - Cytokinesis:
- Division of the cytoplasm usually follows mitosis fairly quickly.
- For cells with a cell wall, a new cell wall forms in the middle of the cell.
