Cell Reproduction (Chapter 10) Flashcards
Cell cycle
All the stages a cell goes through in its life
5 stages in cell cycle
G0 - undergoing normal functions but not dividing
G1 - Growth 1 phase: growing larger, synthesising extra proteins for cell division, still performing normal functions
S - Synthesis phase; DNA molecules are duplicating
G2 - Second growth phase; final preparation and growth before mitosis
M - Mitosis; cell division
The 3 checkpoints in the cell cycle
- Cell growth checkpoint - occurs towards the end of the growth phase (G1). Checks whether the cell is big enough and has made proper proteins for the synthesis phase.
- DNA synthesis checkpoint - Occurs during synthesis phase (S). Checks whether DNA has been replicated correctly.
- Mitosis Checkpoint - Occurs during the mitosis phase (M). Checks when mitosis is complete
Mitosis
Mitosis is a process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei. There is 4 phases:
Prophase
Metaphase
Anaphase
Telophase
A continuous process that is important because it creates new body cells that are needed for growth, repair and maintenance
What occurs in prophase?
-Centrioles become visible, and move to poles of cell
-spindle fibres form from the centrioles
-DNA goes from chromatin to chromosomes
By the end of this stage, the nucleus has disappeared and the chromosomes are making their way to the middle to line up along the cells equator
What occurs in metaphase?
Chromosomes, attached to spindle fibres, are aligned in the middle of the cell.
What occurs in anaphase?
Chromosomes are pulled back by the spindle fibres, splitting into individual chromatids (now called chromosomes again).
Pulled back towards the poles and centrioles.
What occurs in telophase?
Two new nuclei reform around the chromosomes at each pole.
Spindle fibres and centrioles reabsorbed.
Chromosomes relax back into chromatin.
Cytoplasm may start to pinch inwards.
What occurs in cytokinesis?
Cyto = cell and kinesis = split
Protein molecules for a contractile ring that contract the cell in the middle to form a figure 8 shape that gradually deepens until the cell splits into two.
How does cell differentiation occur?
through methylation and acetylation, in which some genes are turned on and others are turned off
How many chromosomes do human somatic cells have versus gametes?
- All human somatic cells have 46 chromosomes - this is referred to as the diploid chromosome number (2n)
- The gametes, or sex cells however have 23 chromosomes - this is referred to as the haplod chromosome number (n)
What is meiosis, and where does it occur?
- Meiosis is a special process of nuclear division which results in the production of sperm or ova
- Meiosis involves two divisions and results in fourdaughter cells
- Each daughter cell contains only half the original number of chromosomes, the haploid number (23 or n).
- It takes place in the sex organs – the testes for
sperm and the ovaries for ovum.
Prophase I
Interphase at the start, DNA is replicated. Doesnt occur before prophase II
- Already replicated chromatin threads condense to form (‘X’ shaped) chromosomes (pairs of chromatids joined by centromere)
- Chromosomes gradually move to equator and find their homologous pair
- Nucleolus and nuclear membrane disappear
- Spindle forms
Metaphase I
- Chromosomes line up at equator, attached to spindle fibres by their centromeres.
- However, this time each chromosome is
lined up side by side with it’s homologous pair
Anaphase I
Spindle fibres contract pulling homologous chromosomes to opposite poles.
Each pole contains one complete set of chromosomes
Telophase I
- Chromosomes uncoil into chromatin, nuclear
membrane forms, spindle disappears. - Cytoplasm divides but no cytokinesis.
What is the purpose of the 2nd meiotic division?
The purpose of the second meiotic division is to
separate the pairs of chromatids so that each gamete has only 23 chromatids (‘half X’ chromosomes).
Prophase II
- New spindle forms that is flipped so horizontal not vertical
- Chromosomes move towards equator
Metaphase II
Chromosomes line up at equator
Anaphase II
- Centromeres divide so that each chromatid is now a separate chromosome
- New chromosomes move to opposite poles
Telophase II
- Nuclear membrane forms and cytoplasm starts to divide
- Cytokinesis occurs producing 4 daughter cells with half the original number of chromosomes.
Crossing over
During Prophase I matching regions on homologous chromosomes may break and then reconnect to the other chromosome.
- This is called crossing over
- The point where two chromatids cross is called
a chiasma
Results in new combinations of genes along the chromosome, and creates genetic variation between gametes.
Three levels of stem cell potency
- Multipotent – most limited, sometimes called adult stem cells can give rise to different cell types within a cell lineage e.g. blood stem cells can give rise to platelets, RBCs, or WBCs but not a bone cell
- Pluripotent – can be come all cell lineages, but not the cells that form the outer layer of the blastocyst
- Totipotent – can become ANY cell, only applies to cells present after first few rounds of division after fertilisation
What is cancer and what are tumours and their two types?
Cancer = uncontrolled cell division.
Tumours are an abnormal mass or tissue of cells that have divided uncontrollably. They can be classified as benign or malignant.
Benign tumours remain in one place. They can’t invade or spread to other parts of the body but they can and do press on surrounding organs.
Malignant tumours can invade other parts of the body. This is known as metastasis and is how secondary tumours form. There can be multiple secondary tumours.
Causes of cancer
Lots of things can cause cancer, including genetic and environmental factors. The environmental factors are called carcinogens. Cancer usually develops after prolonged exposure to carcinogens. Examples of carcinogens include:
- UV radiation
- X-rays
- Ionising radiation
- Viruses
4 major cancer types and their screening
- Cervical, pap smear every 2 years
- Prostate, Digital rectal exam, biopsy
- Bowel, faecal occult blood test
- Breast, mammograms
