Biology Term 1 Flashcards
What is the cell cycle?
A series of events that take place in a cell involving cell growth, DNA replication and cell division.
It is described as the lifecycle of a cell.
State the three stages of the cell cycle
- Interphase
- Mitosis
- Cytokinesis
What is the interphase?
The longest stage of the cell cycle that involves cell growth, the syntheses of new organelles and DNA replication.
What does DNA replication involve?
- Double helix ‘unzips’ exposing two strands.
- DNA bases align next to complementary bases on the DNA strands.
- Complementary base pairs join.
- Tow identical DNA molecules formed.
What is a chromosome?
A linear DNA molecule tightly coiled around proteins.
What happens to chromosomes durning DNA replication?
The DNA in the ‘arms’ of each chromosome (chromatid) is relicated.
What is mitosis?
A form of cell division that produces two diploid ‘daughter’ cells, both genetically identical to the parent cell.
Why is mitosis important in organisms?
- Asexual reproduction
- Growth
- Repair of damaged cells
- Cell replacement
State the four stages of mitosis
P - Prophase
M - Metaphase
A - Anaphase
T - Telophase
Outline prophase
- DNA condenses, chromosomes become visible
- Nuclear membrane disappeared
Outline metaphase
Chromosomes line up along the cell equator.
Outline anaphase
- Spindle fibres attach to each chromosome.
- ‘Arms’ of each chromosome pulled to opposite poles.
- Chromatids separated.
Outline telophase
- Nucleus of the cell divides.
- Nes membrane forms around each set of chromosomes.
What does cytokinesis involve?
- Division of the cell membrane and cytoplasm.
- Two genetically identical ‘daughter’ cells produced.
What is cancer?
- Non-communicable diseases.
- Uncontrolled cell division (due to damaged DNA) results in the formation of a primary tumour.
- Tumour cells break off and spread to other tissues forming secondary tumours.
What are percentile charts?
- A chart used to monitor growth.
- Measurements (e.g. fetal length or head circumference) can be compared to the expected values at a certain age.
What does the 95th percentile mean?
95% of measurements will be below the value of the 95th percentile.
What can doctors determine from the percentile charts?
- Slower growth than normal (below the bottom lines).
- Faster growth than normal (above the top line).
- Abnormal growth (irregular growth patterns).
Describe growth in animals
- Cell division occurs in all body cells. It occurs at a slower rate in adults that in younger animals as growth stops and cell division is only required for replacement and repair.
- Most cells differentiate for early stage and become specialised. Some adult stem cells retain their ability to differentiate.
Describe growth in plants
- Cell division can only occur in meristematic tissue. The rate of cell division remains the same throughout a plant’s life.
- Meristematic stem cells can differentiate into any cell type for as long as the plant lives.
- Cell elongation occurs in all cells. Cells expand and enlarge enabling growth of the plant.
What are stem cells?
Cells that are unspecialised and capable of differentiating into a range of different cell types.
What is meant by ‘differentiation’?
- The process by which stem cells become specialised.
- Some genes switch on or off, determining cell type.
Why is cell differentiation important?
It enables the formation of specialised tissues with specific functions e.g. muscle tissue.
What are embryonic stem cells?
Stem cells found in very early embryos that are unspecialised and capable of differentiating into any cell type.
What is the function of embryonic stem cells?
Enable the growth and development of tissues in human embryos.
What are adult stem cells?
Stem cells that can differentiate into a limited range of cell types e.g. bone marrow stem cells.
What is the primary function of adult stem cells?
Replacement of dead cells e.g. replacement of red blood cells which only live for 120 days.
Where are stem cells founds in plants?
Meristems
Where is meristem tissue found?
In regions of the plant where cells are continuously dividing, e.g. root tips, shoot tips.
Where are meristematic stem cells?
Stem cells found in meristems are unspecialised and capable of differentiating into any cell type during the life of a plant.
How can stem cells be used in medicine?
- Stem cells collected.
- Stem cells stimulated to differentiate into specific cell types e.g. heart muscle cells.
- Specialised cells transplanted into the patient.
- Used to treat damage or disease e.g. heart disease.
Where can embryonic stem cells be collected from?
- Donor stem cells removed from embryos grown in vitro.
- Patient’s own stem cells removed from the umbilical blood before birth.
What are the benefits of using stem cells in medicine?
- Treat damage or disease e.g. heart disease, type 1 diabetes.
- Treat diseases that would otherwise be untreatable.
- Used in scientific research.
- Growing organs for transplants.
What are the risks of stem cells use in mededicine?
- Transplanted stem cells could cause tumours.
- Finding suitable stem cell donors is a difficult task.
- Stem cells may be rejected by the body (immunosuppressants taken).
- Potential side effects.
- Long term risks of using stem cells unknown.
- Stem cells may become contaminated during preparation and when transplanted transmit infections to the patient, making them sicker.
What are the ethical issues related to the use of stem cells in medicine
- The embryos that were used to provide stem cells are destroyed which is seen as unethical and a waste of potential human life.
- May lead to the reproductive cloning of humans.
What is DNA?
A double-stranded polymer of nucleotides, would to form a double helix.
What are the monomers of DNA?
Nucleotides
What are DNA nucleotides made up of?
- Common sugar.
- Phosphate group.
- One of the four bases : A, T, C or G
State the full names of the four bases found in nucleotides?
- Adenine
- Thymine
- Cytosine
- Guanine
Describe how nucleotides interact to form a molecule of DNA?
- Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand.
- Base connected to each sugar.
- Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds.
Define Genome
The entire genetic material of an organism
What is a chromosome?
A long, coiled molecule of DNA that carries genetic information in the form of genes.
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein.
Describe the method used to extract DNA from fruit?
1) Place a piece of fruit in a beaker and crush it.
2) Add detergent and salt, mix.
3) Filter the mixture and collect the liquid in a test tube.
4) Pour chilled ethanol into the test tube.
5) DNA precipitates forming a fibrous white solid.
6) Use a glass rod to collect the DNA sample.
Why is detergent added to the crushed fruit?
It disrupts the cell membranes, releasing DNA into solution.
Why is salt added to the crushed fruit?
Salt encourages the precipitation of DNA.
Why is chilled ethanol added rather water?
DNA is insoluble in ethanol, encouraging its precipitation.
Explain how a gene codes for a protein.
- A sequence of three bases in a gene forms a triplet.
- Each triplet codes for an amino acid.
- The order of amino acids determines the structure (i.e. how it will fold) and function of protein formed.
Why is the ‘folding’ of amino acids important in proteins such as enzymes?
The folding of amino acids determined the shape of the active site which must be highly specific in the shape of its substrate.
What is protein synthesis?
The formation of a protein from a gene.
What are the two stages of protein synthesis?
- Transcription
- Translation
What does transcription involve?
The formation of mRNA from a DNA template.
Outline transcription
- DNA double helix unwinds.
- RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand.
- RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand.
- mRNA formation complete. mRNA detaches and leaves the nucleus.
Describe the difference between mRNA and DNA.
- mRNA is singe stranded whereas DNA is double stranded.
- mRNA uses U whereas DNA uses T
Why is mRNA used in translation rather than DNA?
DNA is too large to leave the nucleus so cannot reach the ribosome.
What does translation involve?
A ribosome joins amino acids in a specific order dictates by mRna to form a protein.
Outline translation
- mRNA attaches to a ribosome.
- Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule.
- A polypeptide chain is formed from the sequence of amino acids which join together.
How is tRNA molecule adapted to its function?
Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries.