- Module 2.1.6 Flashcards
What is a haploid?
A cell with a single set of unpaired chromosomes.
What is a diploid cell?
A cell with two complete sets of chromosomes.
What is a gamete?
A sex cell (pollen/sperm/egg)
What is a zygote?
Formed when two gametes fuse together.
What is a mutation?
A change in an organism’s DNA.
What is mitosis?
Cell division that forms two identical daughter cells.
What is meiosis?
Cell division that forms 4 haploid daughter cells.
How do cells reproduce?
Cells reproduce by duplicating their contents and splitting into two daughter cells.
How does DNA exist in a cell?
It associated with specialised proteins that give it structure.
In eukaryotes these include histones.
The complex of histones and other structural proteins with DNA is called chromatin.
How does chromatin exist in a cell when it is decondensed?
Most of the time it’s decondensed, it exists in thin squiggles, can be seen under a microscope.
In this state it can be easily accessed by cellular machinery (proteins that read and copy DNA), this is important in allowing the cell to function.
How does chromatin exist in a cell when it is condensed?
It takes place when the cell is just about to divide.
When chromatin condenses you can see that eukaryotic DNA is not just one long string, instead it’s broken up into separate, linear pieces called chromosomes.
How many chromosomes do humans have?
Humans have 23 homologous pairs of chromosomes, 46 total.
What are features of a homologous pair of chromosomes?
Two chromosomes in a homologous pair are very similar, they have the same size and shape.
More importantly they carry the same type of genetic information, ie they have the same genes in the same places, but they may have different alleles.
What is the Hayflick constant?
The idea that cells should only undergo a certain number of cycles or divisions. Usually around 40-60. If this is exceeded the cell may be considered cancerous and form a tumour.
What is the order of the cell cycle’s processes?
Interphase - G1, S, G2
Nuclear division/mitosis
Cytoplasmic division/cytokinesis
What happens at G1 of the cell cycle?
The first growth phase, cells grow and increase in size.
Transcription of genes to make mRNA occurs.
Organelles duplicate
Biosynthesis - eg protein synthesis, including making the enzymes needed for DNA replication in the S phase.
What happens in the S (synthesis) phase of the cell cycle?
DNA is replicated in the nucleus.
When all chromosomes have duplicated their DNA, each one consists of a pair of identical sister chromatids.
What happens at G2 of the cell cycle?
The second growth phase.
Special chemicals ensure the cell is ready for mitosis by stimulating proteins that will be involved in making chromatin condense and in formation of the spindle.
Cells continue to increase in size.
Energy stores are increased.
What is G0 and what happens here?
G0 is a resting phase triggered by checkpoints, it is when the cell leaves the cell cycle.
Cells may undergo apoptosis, differentiation or senescence (ageing cells no longer dividing).
Why does G0 happen? What purpose does it have?
Differentiation - cells become specialised and perform this function indefinitely. It won’t enter the cell cycle again.
Damage DNA - means cells can no longer replicate, it isn’t viable.
Age - the older you are the more ‘senescent’ cells you have (linked with cancer and arthritus)
What is the point of checkpoints?
They check to see that the previous part of the cell cycle has been completed.
What is a cancer? How are they formed?
Uncontrolled cell division.
Genes mutate and become oncogenes.
Carcinogens can alter DNA to form oncogenes.
What are the 4 roles of mitosis?
DEVELOPMENT - the formation of multicellular organism from a single fertilised egg.
GROWTH - involves an increase in size through the division of cells by mitosis.
CELL REPLACEMENT - many cells within an organism are constantly dying and being replaced by mitosis.
ASEXUAL REPRODUCTION - asexual reproduction in certain plants and lower eukaryotic animals, involves the process of mitosis.
How do prokaryotic organisms reproduce?
They do not have a nucleus and they reproduce by binary fission.
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens in prophase?
Preparation phase.
Chromatin condenses and chromosomes become visible.
In animal cells + some plant cells, two centrioles migrate to opposite poles of the cell.
Microtubules start to develop spindle shaped structures and span the cell from pole to pole.
By the end of prophase the nuclear envelope breaks down and disappears.
What are centrioles?
Cylindrical bundles of proteins that help in the formation of the spindle.
What happens in metaphase?
Middle
Microtubules from the poles are attached to the centromere.
Chromosomes are pulled along the spindle apparatus to form a plane in the center of the cell, called the metaphase plate and held in position.