Lecture 6 - Chromosomes and Cell Division Flashcards
What are telomeres?
The protective cap at the end of DNA strands
Everytime a cell divides, there is less and less telomere
What do cancer cells do with their telomeres?
They rebuild their telomeres after each division; therefore unable to stop dividing
What are the 2 steps of procaryotic cell division?
1- Replication: Start at 1 specific region, copy all DNA until we have 2 identical circular chromosomes
2- Binary fission: cell elongates and divides into 2 (2 daughter cells formed)
• Happens very quickly
• Considered asexual reproduction
Why do eukaryotic cells divide? (3 reasons)
- Reproduction (reproductive cells)
- Growth and Development (somatic)
- Tissue Renewal (somatic)
What are teh 2 types of eukaryotic cells? How are their division process calles?
1- Somatic cells ○ All cells forming the body of the organism (EXCEPT: sex cells) ○ Division is called mitosis 2- Reproductive cells ○ Sex cells (gametes) ○ Division is called meiosis
In mitosis, what are the three parts of the Interphase?
- Gap 1 - Cell grows, performs functions,
- G0 - Lil break - cell does not divide
- S phase (DNA synthesis)
i. DNA of parent is divided into 2 strands
ii. Complementary nucleotide passes through and attaches to each half (A-T, G
iii. Product: 2 identical daughter DNA molecules (duplicated chromosome)
i. Called sister chromatids: held together at the center centromere - Gap 2 - significant growth (spindles form)
In mitosis, what are the 4 parts of the mitotic phase? Does this part happen before or after interphase?
• Prophase:
○ Nuclear membrane breaks down
○ Sister chromatids condense
○ Spindle forms
• Metaphase:
○ Sister chromatids line up at the center of the cell (spindle fibers pulling these)
• Anaphase:
○ Break apart the chromatids and pull them in opposite directions (now called individual chromosomes) (1 set goes to each side)
• Telophase
○ Chromosomes begin to uncoil as nuclear membrane reassembles around them
○ Cell begins to pinch in 2 (become 2 separate cells)
○ Cytokinesis also starts here
What are the 3 checkpoints during mitosis?
1- G1/S: is DNA damaged? Is growth possible?
2- G2/M: had DNA been replicated properly?
3- Spindle assembly: are the spindle fibers properly built/attached?
What happens if a cell does not pass a checkpoint?
Cells cannot divide because they do not pass these checkpoints
Cancer: when a cell stops respecting checkpoints
What are spindles? What do they do?
- Set of proteins, mostly hollow tubes called microtubules
- Stretch across the cell between its 2 ends, or poles
- Attached to centromeres, and centrioles (outside of nucleus)
- Physically pull the sister chromatids to the middle of the cell, then pulls them appart for cell division
How many chromosomes do we have in the nucleus of our cells?
46 (23 pairs, one from mom and one from dad)
-There are 23 KINDS of chromosomes (each cells has 2 of each kind)
What is a cancer? How does it happen?
• Defined as unrestrained cell growth / division
○ No “contact inhibition” (normal cells stop division when they touch other cells)
• Cells do not pass the checkpoints anymore
• Can damage adjacent tissue
• These cells do not stick together (and spread everywhere in your body)
What is the difference between malignant and benign tumors?
- Malignant tumor: can spread
* Benign tumor: cannot really spread
What are the solutions to cancer?
Chemotherapy/radiation therapy
What is the purpose of meiosis?
To make gametes (sperm and eggs)
What is the starting point of meiosis and the results?
- Starting point: Diploid cell (2 sets of 23 chromosomes) (somatic cells are diploid)
- Generates haploid cells (1 set of 23 chromosomes)
Why is meiosis important?
It maintains a stable genome size (otherwise kids would always have double the chromosomes of their parents)
Why is it important that meiosis produces gametes different from each other?
○ More chances of creating better genetic combinations as offspring
What are homologous chromosomes?
The maternal and paternal copies of a chromosome
What are sister chromatids
The 2 identical copies of a chromosome created during replication (held together by centromere)
Which part of the cell division process is the same in mitosis as it is in meiosis?
Interphase
What are the 2 phases that replace mitosis in meiosis?
- Meiosis division 1
A. Separating the homologues from each other
B. Prophase 1
i. Crossing Over: 2 “legs” of sister chromosomes cross over and exchange (become a combination from mom and dad’s cells) (see image) (called recombination)
C. Metaphase 1
i. Each pair of homologous chromosomes moves to the equator of the cell (line up w their homologous partners rather than alone like in mitosis)
D. Anaphase 1
i. Beginning of 1st cell division in meiosis
ii. Each homologous goes into either of the cells
E. Telophase 1 and cytokinesis
i. Cell actually splits in 2 - Meiosis Division 2
*NO INTERPHASE (no replication)
A. Prophase 2
i. Chromosomes in daughter cells condense, spindle forms
B. Metaphase 2
i. Sister chromatids move to center of cell
C. Anaphase 2
i. Fibers pull chromosomes apart
D. Telophase 2
i. Envelope reforms, membrane pinches off
What is the outcome of meiosis?
4 haploid daughter cells
What is the difference in the production of male and female gametes?
Males - 1 sperm divides into 4
Females - the cytoplasm will not divide equally between the 2 new cells, therefore one will not be a viable egg, so it produces one haploid cell
