Genetics Flashcards
What are the two types of nucleic acid?
- DNA
- RNA
What are the three parts that a nucleotide is made up of?
A sugar with 5 carbon atoms (a pentose sugar)
A phosphate group – this is the acidic, negatively charged part of nucleic acids
A base – contains nitrogen and has either a single ring (pyrimidine) or double ring (purine) structure.
What are the 4 bases that DNA is made out of?
adenine
thymine
guanine
cytosine
What is the difference between DNA and RNA?
DNA is a double stranded polymer whereas RNA is a single-stranded polymer.
DNA contains the nitrogenous bases – adenine, thymine, guanine and cytosine.
RNA contains the nitrogenous bases – adenine, uracil, guanine and cytosine.
How many bonds does adenine and thymine join by?
2 hydrogen bonds
How many hydrogen bonds does cytosine and guanine bond by?
Three hydrogen bonds
State the type of bonds that links base pairs in a DNA molecule
Hydrogen bond
State the type of bonds that connects DNA nucleotides in a single strand.
Covalent bond
Phosphodiester linkage
Outline the steps of DNA replication
- An enzyme called helicase causes the DNA double helix to progressively unwind. Helicase then use energy from ATP to break the hydrogen bonds between complementary base pairs and the two strands of DNA separate
- Nucleotides are added to each single strand – Each separated strand acts as a template for the new strand. An enzyme called DNA polymerase takes nucleotides (already assembled and free floating in the nucleus) and creates a complementary strand to the exposed strand - matching A with T and G with C
- A different DNA polymerase checks the base pairing and edits any incorrect additions – incorrect base pairing results in a change in DNA sequence (a mutation). It also forms the covalent bonds between the sugar and phosphates of subsequent nucleotides.
Outline the steps of semi-conservative replication
In 1958 Matthew Meselson and Franklin Stahl published the results of exceedingly elegant experiments that provided very strong evidence for semi-conservative replication.
They grew E.coli in a medium containing a heavier isotope of Nitrogen (N-15) for a number of (20 minute) generations. The nitrogen in the media was used to synthesise new DNA as the bacteria duplicated their genomes.
They then transferred the bacteria to a N-14 medium (normal nitrogen).
The bacteria could then use only the available N-14 to incorporate into new DNA. The samples were collected and their density measured.
Outline the steps of the polymerase chain reaction
- Denaturation of target DNA to separate the strands at the hydrogen bonds between complementary base pairs. This happens at 95℃.
- Annealing (binding) of short complementary primers to the matching section of the target DNA, typically at 50-60℃ (higher temperatures require better matches for binding of primers).
- Extension of new DNA strands from primers by deoxy-nucleotide bases (dNTPs where N= A,T,C or G) to create a second copy of the target sequence. This step occurs at 72℃ the optimal temperature for Taq polymerase enzyme to synthesise new strands.
Introns
- Non-coding sequences.
- In many eukaryote genes, the coding sequence is interrupted by one or more non - coding sequences.
- These introns are removed from mRNA before it is translated.
An intron is any nucleotide sequence within a gene that is removed by RNA processing during production of the final RNA product.
Telomeres
- Repetitive base sequences at the end of the chromosomes.
- Telomere prevents parts of important genes at the ends of the chromosomes from being lost each time DNA is replicated.
List what is involved in an oxidation reaction
- Addition of oxygen atoms to a substance.
- Removal of hydrogen atoms from a substance.
-Loss of electrons from a substance.
Summarise the steps of glycolysis
- One glucose is converted into two pyruvates.
- Two ATP molecules are used per glucose but four are produced so there is a net yield of two ATP molecules.
- This is a small yield of ATP per glucose, but it can be achieved without the use of oxygen.
-TWO NADs are converted into two reduced NADs.
Define a genome
The genome is the whole of the genetic information of an organism.
The size of a genome is the total amount of DNA in one set of chromosomes in a species.
Compare and contrast the properties of homologous chromosomes
Compare:
-Same length
-Same centromere
-Same sequence of genes
Contrast:
- Different alleles.
What is an allele?
Different forms of a gene
Outline the steps of Prophase I of meiosis
-Chromosomes pair up. The chromosomes in each pair are homologous.
- Spindle microtubules grow from each pole to the equator as in mitosis.
- Nuclear membrane will soon disintegrate,
Define synapsis
The fusion of chromosome pairs at the start of meiosis.
What are bivalent pairs?
The paired chromosomes after synapsis are called bivalent pairs.
Outline the function of amniocentesis
- A sample of amniotic fluid which is removed from the amniotic sac around the fetus.
- A hypodermic needle is inserted through the wall of the mother’s abdomen and wall of the uterus.
- Amniotic fluid is drawn out into a syringe. It contains cells from the fetus.
Outline the function of chorionic villus sampling
- Cells are removed from the fetal tissues in the placenta called the chorionic villi.
- CVS has a (2%) chance of miscarriage.
What is cystic fibrosis?
This disease is caused by a recessive allele of a gene coding for a chloride channel.
What is Huntington’s disease?
A neurodegenerative disease is caused by dominant alleles of the gene coding for hunigtin.
What is an autosome?
An autosome is one of the numbered chromosomes, as opposed to the sex chromosomes.
Outline the properties of sickle-cell anemia
- A genetic disease that is caused by base substitution mutation.
- The mutation changes HbA into a new allele, HbS.
- One codon in the mRNA is difference, thus one amino acid in the polypeptide is altered.
- Valine codon
- Sickle cells may carry oxygen less efficiently but can give resistance to malaria.
