1: Cell Cycles and Cancer Flashcards
What is the cell cycle?
the sequence of events between one cell division and the next
State the main phases of a cell cycle.
interphase and cell division
Describe (briefly) interphase.
very active phase in the life of a cell when many metabolic reactions occur
Which metabolic reactions happen only in interphase?
- DNA replication in the nucleus
- and protein synthesis in the cytoplasm
What happens to the number of mitochondria and chloroplasts in the cytoplasm?
the numbers increase as they grow and divide
How many phases in interphase? Name them all.
three:
- G1 phase
- S phase
- G2 phase
What happens in S phase? Why?
cell replicates all the genetic material in its nucleus, so that after mitosis both the new cells have a complete set of genes
Which phase in interphase does a cell stay at if it will not divide again?
G1 - they will never divide again so do not need to prepare to mitosis
What happens at the end of interphase?
the cell begins mitosis, where the nucleus divides to form two genetically identical nuclei
What happens at the end of mitosis?
cytokinesis - the cytoplasm of the cell starts to divide and two cells are formed, each containing one nucleus
What are cyclins?
a group of proteins used to ensure that tasks in the cell cycle are performed at the correct time and that the cell only moves on to the next stage of the cycle when it is appropriate
Describe how cyclins act in general.
- cyclins bind to enzymes called cyclin-dependent kinases
- kinases then become active and attach phosphate groups to other proteins in the cell
- attachment of phosphate triggers other proteins to become active and carry out tasks specific to one of the phases of the cell cycle
How many main types of cyclins are there in human cells?
4
How do cyclins control the cell cycle? What does this ensure?
- cell can only only progress to the next stage in the cell cycle when the relevant cyclin reaches a ‘threshold level’
- cyclins therefore control the cell cycle.
- ensures that cells divide when new cells are needed, but not at other times
Sketch a cyclin concentration graph over 4 phases of the cell cycle (3 phases in interphase and mitosis). (p15)
should have 4 cyclins: D, E, A, B
How were cyclins discovered?
serendipity - happy accident:
- Tim Hunt doing research into protein synthesis in sea urchin eggs
- he noticed a protein that increased and decreased in concentration repeatedly, the increase/decrease corresponded with particular phases of the cell cycle
- he named the protein cyclin
- discovery partly due to luck but also due to being observant and realizing the significance of an unexpected observation
What is ‘oncogenesis’?
formation of tumours
Where does the process of oncogenesis start?
with mutations in genes involved in the control of the cell cycle called oncogenes
What must happen for control of the cell cycle to be lost?
mutation must occur in SEVERAL oncogenes in the same cell
The chance of mutation occurring in several oncogenes in the same cell is minute. How come human cells get cancer?
body contains billions of cells, any one of which could have mutations in its oncogenes, so the overall risk is significant
What increases the risk of tumour formation?
anything that increases the chance of mutation
What are mutagens?
chemical substances that can cause mutations
Name two causes of tumour formation.
- mutagens - chemical substances that can cause mutations
- ionizing radiation
What happens when control of the cell cycle is lost?
cell undergoes repeated uncontrolled divisions that produce a mass of cells called a primary tumour
What is often the case with primary tumours?
- they are often benign
What qualities does a tumour have if it is ‘benign’?
- does not grow rapidly
- does not spread
What is the opposite of ‘benign’ when describing tumours? What qualities does this sort of tumour have?
- malignant
- grows rapidly
- spreads
What can happen if a cell becomes detached from the primary tumour?
- cell carried elsewhere in body
- develops into a secondary tumour
Define metastasis.
the spreading of cells to form tumours in a different part of the body
When is a patient said to have cancer? What happens if cancer is not treated?
- when they have a secondary tumour
- if not treated, the cancer will likely lead to the patient’s death
What is the relationship between cigarette smoking and the death rate due to cancer?
positive correlation - more cigarettes smoked per day = higher chance of developing cancer of the lung and some other organs
What does the correlation between smoking cigarettes and the death rate due to cancer prove by itself?
that there is a correlation. It does not prove that smoking cigarettes CAUSES cancer in some organs
“There is evidence that chemicals in tobacco smoke are … and therefore …. (cancer causing)”.
- mutagenic
2. carcinogenic
