Session 1 - The Cell Cycle and DNA Replication Flashcards
How do prokaryotic cells divide their nuclear material?
Binary Fission. When a cell splits via binary fission its functions are unaffected. There are many copies of looped DNA in a cell and half of the copies goes to one daughter cell, and the other half goes to the other daughter cell (so each new cell has at least one copy of DNA)
Why does mitosis occur?
- For growth, multicellular organisms grow by increasing their number of cells. 2. Some eukaryotic organisms reproduce asexually using mitosis. 3. for tissue repair/replacing dead or damaged cells. 4. for embryonic development: a fertilized egg will undergo mitosis to develop into an embryo.
Overall, what are the three stages of interphase?
Stage G1: Cellular contents are duplicated. Stage S: each of the 46 chromosomes are duplicated (DNA replication). Stage G2: the cell then “double checks” the chromosomes and makes any necessary repair if there is error, and then the cell splits into two.
What are cyclins and what do they do?
They are a group of regulatory proteins that control the cell cycle.
How do cyclins operate within the cell?
There are four main types of cyclins in human cells, and a necessary amount of each one is needed to progress to the next phase of the cell cycle. They peak when their target protein is required for function and remain at lower levels at all other times.
Specifically, how do cyclins control the cell cycle?
They bind to enzymes called cyclin-dependent kinases (CDKs) that become active and together they form a complex. This complex binds to a target protein and modifies it via phosphorylation. The phosphorylated target protein will trigger some specific event within the cell cycle (e.g. centrosome duplication, etc.). The cyclin then degrades and the CDK becomes inactive again.
What are the main parts/stages of the cell cycle?
Interphase
Mitotic division
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
What are chromosomes like during interphase and before dividing?
Interphase: single-armed structures in their unwound state
Dividing: double-armed structures, having replicated their DNA to form two chromatids in preparation for cell division.
What happens during prophase?
DNA supercoils and chromosomes condense, Nuclear membrane breaks down, and paired centrosomes move to poles
What happens during metaphase?
Microtubule spindle fibres connect from centrosomes at the edges of the cell to centromeres of chromosomes, then the spindle fibres contract, causing the chromosomes to align at the centre
What happens during anaphase?
Spindle fibre contraction cause the sister chromatids to separate and become identical chromosomes that
move to opposite poles of cell
What happens during telophase?
The chromosomes de-condense, Nuclear membranes reform around the two identical chromosome sets, Cytokinesis (division of the cell) occurs
What is the Cytokinesis stage of mitosis?
Occurs at the end of mitosis and is different in plant and animal cells. In plants: vesicles are moved to the equator were they fuse to form a tubular structure which merges with more vesicles to form the plasma membrane and divide the cytoplasm. Substances such as pectin and cellulose are then deposited by exocytosis to form the lamella and cell wall. (unlike animals, there is no pinching at the equator, instead the vesicles form a new cell wall at the equator to split the two daughter cells. For animals: the plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow by contractile proteins actin and myosin – the same as in muscles.
What is the difference between eukaryote and prokaryote?
Eukaryote: DNA is stored in nucleus. Prokaryote: DNA is stored in cytoplasm.
What is semiconservative replication?
It’s how DNA double stranded structure allows it to split the strands apart with each one providing the basis for a new complementary strand. Each new double stranded daughter strand contains both new and parental DNA, so the original copy is “semi” conserved.
