notes Flashcards
Binary fission
The division of a cell into 2 without mitosis; the process by which a prokaryotic cell splits to form 2 daughter cells.
- Similar to mitosis but occurs in prokaryotic cells as there is only one chromosome and no centromere.
Process includes:
- DNA replication
- Chromosome segregation
- Cytokinesis
- Produces 2 daughter cells with identical DNA to parent cell
Occurs in eukaryotic cells but only for producing:
- Mitochondria
- Chloroplasts
Apoptosis example
The death of cells which occurs as a normal and controlled part of an organism’s growth or development.
Example of Apoptosis :
- Enables tadpole to lose its tail as it becomes a frog
- Allows human embryo to lose the webbing between its fingers and toes
Failure in Apoptosis
Failure in Apoptosis can result in many problems, ranging from development defects to cancer
- Formation of cancer happens when apoptosis is avoided and cells do not die as they should
Cell cycle checkpoints
G0 - resting state
- Doesn’t divide or preparing for division
- Occurs outside of cell cycle
- Damaged cells are located here
G1 checkpoint Check for: - Cell size - Nutrients - Growth factors - DNA damage
G2 checkpoint
Check for:
- Cell size
- DNA replication
Mitosis checkpoint - spindle assembly checkpoint
Check for:
- Chromosome attachment to spindle
Tumor suppressor genes
- Inhibit cell division
- Normal genes that slow down cell division
- Repair DNA mistakes
- Tell cells to when to die
Chemical mutagens
- Ability to interfere with DNA
- Interrupts its structure, sequence and replication
Physical mutagens
- Ultraviolet light, X rays and nuclear radiation
- When UV light is absorbed DNA is damaged
- Mutations in tumor suppressor gene p53 play a critical role in development of precancerous lesions and have been implicated in all types of skin cancer
Biological mutagens
- Viruses - take over cells
- Impair cell cycle regulation - results in cancer
- Cause uncontrolled cell growth
Stem cells
Stem cells are undifferentiated cells that have the potential to replicate and to develop into many different kinds of cell
Stem cells ( Asexual reproduction)
Stem cells are undifferentiated cells that have the potential to replicate and to develop into many different kinds of cell
Totipotent stem cells ( Asexual reproduction)
Ability to form embryo and membranes that will surround, support and nourish it
Example = the early embryo before formation of inner cell mass
Pluripotent stem cells ( Asexual reproduction)
Capable of giving rise to most but not all tissues of an organism
Example = the inner cell mass
Multipotent stem cells ( Asexual reproduction)
Able to give rise to cells that have a specific function
Example = blood stem cells
Fission ( Asexual reproduction)
- Single celled eukaryotic or prokaryotic organisms
- Divide into 2 new organisms
- Each is an exact copy of parent cell
- Nucleus is replicated and cytoplasm splits to form 2 new daughter cells
Budding ( Asexual reproduction)
- New organism is grown on the outside of the parent organism
- Eventually detaches as its own complete organism
- Hydra, yeast
Vegetable propagation ( Asexual reproduction)
- Only in plants
- Plants grow from cuttings
- New plant forms through mitosis - genetically identical to parent plant
- Plant grows - cells undergo differentiation and become specialised
- Used for agricultural purposes to replicate qualities in plants
Spore formation ( Asexual reproduction )
- Spores are hardy self contained capsules - single celled structures
- Contains exact copy of DNA of the parent
- Can form an entire new organism in right conditions
Spores can survive for hundreds of years and still germinate - Prokaryotes, fungi, plants
Disadvantages of asexual reproduction in certain situations
- Offspring are genetically identical
- Parental care of offspring is limited or none
- Large numbers of offspring may compete for limited resources
- Lack of genetic diversity
Nuclear transfer
- Process made famous in 1996 - Dolly the sheep
- Nucleus of adult sheep’s mammary cell taken and inserted into ovum - which has nucleus removed
- Resulting blastocyst transferred to surrogate mother
Method has very low success rate for live births
-
Nuclear transfer ( Asexual reproduction )
- Process made famous in 1996 - Dolly the sheep
- Nucleus of adult sheep’s mammary cell taken and inserted into ovum - which has nucleus removed
- Resulting blastocyst transferred to surrogate mother
Method has very low success rate for live births
-
Issues of cloning ( Asexual reproduction)
If we’re using adult cells and putting them into eggs to form blastocyst
- Gamete cells - stem cells in embryo that allows offspring to survive.
- Not successful as cells are different and the adult cells aren’t stem cells
- Can’t use adult cells for cloning but you may be able to use adult stem cells instead
It is failing because they aren’t using stem cells
Multiple allele
Multiple allele are controlled by a single gene but many alleles.
Polygenic inheritance
characteristic controlled by more than one gene is known as a polygenic characteristic.
Continuous
When traits show a range of phenotypes they are called continuous variation whereas only one gene is involved and results in a small number of phenotypes called discontinuous variation.
Pure Breeding
A line of organisms that always produce offspring with the same phenotype when crossed with each other.
Nucleotides
The basic building block of nucleic acids (DNA and RNA), which are linked together by phosphodiester bonds; each nucleotide is made up of a five carbon sugar, a phosphate group and a nitrogenous base
Nucleotide base pairs
Two complementary nucleotide bases that are joined together by hydrogen bonding in a DNA double strand
Autosome
A chromosome that is the same in both males and females of a species, autosomes do not include sex chromosomes
Nitrogenous base
A structural component of nucleotides, DNA has adenine (A), cytosine (C), guanine (G) and thymine (T), in RNA thymine is replaced with uracil (U).
Monoploidy
An individual that contains one half the normal number of chromosomes is a monoploid and exhibits monoploidy. Monoploids are very rare in nature because recessive lethal mutations become unmasked, and thus they die before they are detected.
Polyploidy
When a cell or organism has a genome compromising three or more copies of each chromosomes, represented by 3n, 4n, 5n, 6n etc. (more than two paired homologous pairs)
Aneuploidy
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46.
Trisomy 21 (Down syndrome)
The condition in which is caused by an extra copy of chromosome number 21.
Klinefelter’s syndrome (XXY syndrome)
A genetic condition in which a male is born with an extra copy of the X chromosome
