| What is the cell cycle? (8) | events which lead to the cell dividing into 2 daughter cells
Interphase - happens before division has 3 stages:
G1 =cell growth and metabolism
S = DNA replication
G2 = Cell growth and preparation
M Phase - cells divide to create 2 daughter cells 2 stages:
Mitosis = nuclear division
Cytokinesis = cytoplasmic division |
| What is mitosis? | process of nuclear division whereby copied DNA molecules are arranged into 2 nuclei |
| What happens during interphase? (4) DOCT | DNA replication (DNA copied during the S phase)
Organelle duplication (organelle copied for twin daughter cells)
Cell growth (cytoplasmic volume increases before division)
Transcription / translation (key proteins and enzymes are synthesised) |
| How is DNA usually packed in the nucleus? (2) | chromatin = loosely packed in an accessible form in the nucleus
can be transcripted and translated |
| How is DNA packaged before cell division? (4) | chromosome = chromatin supercoils to become tightly wound and condensed
easily grouped but inaccessible for transcription
condenses in prophase
decondenses in telophase |
| How is DNA packed during the S phase in interphase? what happens after? (2) | during S phase, the chromosome has 2 identical DNA strands (sister chromatids) which is held in the middle with centromere
During mitosis when they separate they are each made of a single DNA strand = daughter chromosomes |
| What are the 4 stages of mitosis? PMAT | Prophase
Metaphase
Anaphase
Telophase
division of cell in two (cytokinesis) is after the final stage |
| What happens during interphase? (3) | DNA is uncondensed (Chromatin) and is in the nucleus
organelles are duplicated
cell is enlarged for division |
| What happens during prophase? (PRO = before) (3) spindles | DNA supercoils and chromosomes condense (made of identical sister chromatids)
paired centrosomes moved to the opposite poles of the cell and form microtubule spindle fibres
nuclear membrane breaks down |
| What happens during metaphase? (MIDDLE) (3) | Chromosomes align in the middle
microtubule spindle fibres connect to the centromeres of each chromosome
spindle fibres contract bec of microtubule depolymerisation |
| What happens during anaphase? (AWAY) (2) | sister chromatids separate and move to opposite poles of the cell
because of spindle fiber contraction |
| What happens during Telophase? (3) | spindle fibres dissolve
chromosomes decondense
nuclear membrane reforms around the 2 chromosome sets |
| What happens during cytokinesis? | LAST STAGE: cytoplasmic division whereby the cell splits into 2 |
| Describe cytokinesis in animal cells? (3) | microtubule filaments form a ring (cleavage furrow) which contracts in the center of the cell
cells become PINCHED off = 2 cells are formed
cells separation = centripetal (starts outside and moves to the centre) |
| Describe cytokinesis in plant cells? | vesicles form at the centre of the cell and fuse to form an early c plate
cells separation = centrifugal |
| What is the mitotic index? what is it used for? (3) | a measure of the proportion of dividing cells
mitotic index increases during cell division
is used to predict the response to chemotherapy from cancer cells |
| mitotic index formula | cells in mitosis / total cell number |
| How would you identify mitotic cells? | they lack a clearly defined nucleus and the condensed chromosomes are visible
P = chromosomes are condensed in a nucleus
M = chromosomes are aligned in the middle
A = 2 clusters of chromosomes at poles of the cell
T = 2 nuclear regions in a single cell |
| Functions of mitotic division (TOAD) | Tissue repair = damaged / aged cells are replaced with new cells
Organismal growth = multicellular organisms make new cells
Asexual reproduction = natural cloning (vegetative propagation)
Development of embryos = zygotes divide and differentiate to form embryos |
| What are the cell cycle checkpoints to regulate the cell cycle? (3) | G1 = checks if the cell is ready for DNA replication (S phase)
G2 = checks if the cell is ready for mitosis
M = checks that the cell is ready for cytokinesis |
| What are cyclins? What do they activate? what do they do? (4) | 1) family of regulatory proteins that control cell cycle progression
2) activate cyclin dependent kinases (CDK) by forming a complex with it
3) The complex phosphorylates a target protein = a specific cell cycle event
4) After the event the cyclin is degraded and CDK inactivated |
| Why do cyclin concentrations need to be tightly regulated? (3) | to make sure the cell cycle happens in a proper sequence
diff cyclins bind and activate diff CDKs
cyclin levels peak when their target protein is needed for function and remains at lower levels at other times |
| How does cell death occur? | once cells reach their proliferative capacity = cell division stops |
| What is the aging phase for cells called? | senescence (aging) phase = cell death |
| What are the two different types of cell deaths? | cell death can be uncontrolled (necrosis) or programmed (apoptosis) |
| What is the difference between apoptosis and necrosis (2) | Apoptosis -
controlled destruction of a cell in response to molecular signals
uses mitochondrial proteins
cell contents are packaged into vesicles and recycled
Necrosis -
premature death due to injury or nutritional deprivation
cells becomes destabilised
Cell contents are released into tissues = inflammation |
| What is cancer? | uncontrolled cell division and can occur in any tissue or organ |
| What is a tumor? 2 types | the abnormal cell growths formed from cancer (uncontrolled cell division)
Primary = stay in the original tissue (BENIGN GROWTHS)
Secondary = invade neighboring tissues (MALIGNANT GROWTHS) |
| What is metastasis? | spread of cancerous tissue from one place to another |
| How are secondary tumors defined? | defined and treated according to the original cell type
eg: breast cancer spreads to liver = secondary breast cancer of the liver |
| What is a mutagen? example? (4) | an agent that causes a change in the genetic material of an organism
either acts on the DNA or replicative machinery
can be physical, chemical or biological
carcinogens = formation of cancer |
| Examples of physical mutagens? (Radiation) (3) | X-rays (ionising) = medical
UV (sunlight)
radioactive decay |
| Examples of chemical mutagens? (3) | Carcinogen (cigarettes)
processed foods
cleaning products |
| What is the mutagen that leads to the formation of cancer? | carcinogens |
| What are examples of biological mutagens? (3) | viruses (HPV)
bacteria (helicobacter)
mobile genetic elements (transposons) |
| What is an oncogene? | a gene that could cause cancer |
| Which mutations to 2 genes causes cancer? | proto-oncogenes = code for proteins that increase cell growth When mutated: cancer causing oncogene
tumor suppressor genes = code for proteins that repress cell cycle progression and promotes cell death
= if mutated or undergoes increased expression it becomes a cancer causing oncogene |
| What is the correlation between smoking and lung cancer? | There is a positive correlation 90%
Cancer rates are higher in countries with higher rates of smoking
increases risk of other cancers such as mouth, stomach, liver |
| how many chemical compounds are there in cigarettes and how many are carcinogenic? | 4000 , 60+ carcinogenic |
