Topic 2.3 Flashcards
DNA replication
DNA replication occurs before cell division so that each new cell has the full amount of DNA
-> this method is called semi-conservative replication because half the strands in each new DNA molecule are from the original DNA molecule meaning there’s genetic continuity between generation of cells
DNA replication steps
- DNA helicase breaks down hydrogen bonds between the bases of entire DNA molecule
- Free DNA nucleotides attach to both strands as both original strands act as template strands through complementary base pairing forms hydrogen bonds
- DNA polymerase joins the nucleotides of the new strands together through phosphodiester bonds by a condensation reaction forming sugar phosphate backbone
- Each new DNA molecule consists of one polynucleotide strand from original DNA molecule and one new polynucleotide strand -> this is what makes process semi-conservative
Meselson and stahl’s experiment
Before meselson and stahls experiment people were unsure whether DNA replication was semi-conservative or conservative
-> conservative means that the original DNA strands would stay together and the new DNA molecules would contain two new strands
Meselson and stahl’s experiment steps
- Two samples of bacteria were grown—one in a nutrient broth containing light nitrogen and the other in a broth containing heavy nitrogen.
- As the bacteria reproduced, they took up nitrogen from the broth to make nucleotides for new DNA making nitrogen gradually part of the bacteria’s DNA
- A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge -> DNA from the heavy nitrogen bacteria settled lower down the centrifuge tube than DNA from the light nitrogen bacteria—because it’s heavier.
- Then, the bacteria grown in the heavy nitrogen broth were taken out and grown in a broth containing only light nitrogen for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge.
-> a) If replication was conservative, the original heavy DNA would still be together and would settle at the bottom, while the new light DNA would settle at the top.
-> b) if replication was semi- conservative then the DNA would settle between where the light nitrogen DNA settled and where the heavy nitrogen DNA settled - DNA replication proven to be semi-conservative as DNA settled out in the middle showing that DNA molecules contained a mixture of light and heavy nitrogen
Mutations
Changes to the base sequence of DNA
-> they can be caused by 5 types of errors during DNA replication
Mutation errors -> substitution
One base is substituted with the other
Mutation errors -> deletion
One base is deleted
Mutation errors -> insertion
An extra base is added
Mutation errors -> duplication
One or more bases are repeated
Mutation errors -> inversion
A sequence of bases is reserved for
Consequences of mutations for proteins
The order of bases in a gene determines he order of amino acids in a particular protein so if a mutation occurs in a a gene the primary structure of the protein it codes for could be altered
-> this means that the sequence of R groups is different and so the bonds/ interactions formed in the tertiary structure are also different causing the protein to change shape and so it doesn’t work properly
Gene
Sequence of bases on a DNA molecule that code for a protein which result in characteristic
Allele
Different version of a gene
Genotype
Alleles a person has
Phenotype
Characteristics displayed by organism
Dominant
An allele whose characteristic will always appear in the phenotype if present in genotype
Recessive
An allele whose characteristic only appears in the phenotype if no dominant allele present in genotype
Incomplete dominance
When trait of dominant allele isn’t completely shown over the trait produced by the recessive so both alleles influence the phenotype
Homozygous
An organism that carries two copies of the same allele for a certain characteristic
Heterozygous
An organism that carries two different alleles for different alleles for a certain characteristic
Carrier
Someone who has one dominant and one recessive allele (heterozygous) where the recessive allele causes a disease -> they don’t have the disease but they carry a copy of the allele for that disease
Monohybrid inheritance
Inheritance of a single characteristic controlled by a single gene with different alleles
-> genetic diagrams can be used to predict the genotypes and phenotypes of the offspring produced when two parents are crossed
Spotting dominant traits
. More individuals with the phenotype
. Phenotype present in almost all generations
Spotting recessive traits
. Fewer affected individuals
. Affected phenotype can skip generations
CFTR
Cystic fibrosis transmembrane conclutance regulator -> channel membrane protein
-> this gene codes for production of chloride ion channels required for secretion, sweat and digestive juices
-> a mutation in this gene leads to production of non functional chloride channels
Cystic fibrosis
Inherited disorder cause by a recessive allele that mainly affects the respiratory, digestive and reproductive system
-> cystic fibrosis causes the production of sticky mucus
Person without cystic fibrosis
- CFTR channel protein allows movements of chloride ions out of the cell
- This movement of ions increases solute concentration out of cell
- Water move out of cell by osmosis and dilutes mucus
Person with cystic fibrosis
- Mutant/ dis functional CFTR channel protein doesn’t allow the movement of chloride ions (by facilitated diffusion) out of cell
- Solute concentration remains low out of cell
- Water doesn’t move out of cells and therefore doesn’t dilute mucus -> stays thick
Effects of cystic fibrosis on respiratory system
Thicker mucus:
. Frequent bacterial infections due to mucus stuck in respiratory system
. Thick mucus adds layer to airways, increasing diffusion distance
. Airways are blocked so less O2 supply -> ventilation less effective therefore less steep concentration gradient
. Breathing difficulties
Treatment of cystic fibrosis for respiratory system
. Physiotherapy -> stretches, massages, exercises etc to help movement of mucus
. Antibiotics
Effect of cystic fibrosis on digestive system
. Mucus blocks pancreatic duct -> fewer enzymes releases to small intestine -> fewer products of digestion
> less absorbance = decreased concentration gradient
. Mucus increases diffusion distance
Effects of cystic fibrosis on reproductive system
Mucus in reproductive system helps to prevent infractions and transport sex cells
. Males: sperm duct blocked
. Females: cervical mucus is thicker -> sperm can’t reach egg as easily and prevents cilia from moving egg
