Cell Replication Flashcards
What is the cell theory?
- All living organisms are made of cells
- Cells are the basic unit of life
- All cells come from pre-existing cells
What are somatic cells?
Cells that aren’t gametes
What are the two types of cell division?
Mitosis - production of diploid somatic cells
Meiosis - production of haploid gametes
Why do cells replicate?
- Restore nucleus to cytoplasm ratio
- Growth and development
- Maintenance and repair
What is the cell cycle?
Life cycle of a cell involving growth, replication of DNA and division to produce two identical daughter cells
In the cell cycle, what is the main focus of the interphase stage?
The cell doubles its mass and duplicates its entire components
In the cell cycle, what is the main focus during mitosis and cytokinesis?
During mitosis, the nucleus divides.
During cytokinesis, the cytoplasm divides (marks two new cells)
What is mitosis?
Division of the nucleus into 2 genetically identical daughter nuclei
Function of mitosis
Growth, repair, maintenace
What are the phases of mitosis?
Interphase, prophase, metaphase, anaphase, telophase
What is a centromere?
Centromeres are the centre of the chromosomes (holds the chromatids together)
Process of Interphase
Duplication of cell insides e.g. organelles, nucleus, chromosomes etc.
Process of Prophase (in general)
- chromosomes condense
- nucleus disappears
- centrioles form spindle fibres and attach to the centromere of chromosomes
Process of early prophase
- Condensing of chromosomes (shorten and thicken, can be visible under the microscope)
- Centrosomes separate
- Nucleus dissolves
- Formation of the mitotic spindle
Process of late prophase
- nuclear membrane breaks down
- centrioles begin to form a network of fibres called spindle fibres (goes to the two poles of a cell)
- centromere of each individual chromosomes attaches to spindle fibres
Process of metaphase
- Chromosomes align in the middle of the cell
- Spindle fibres attach to centromeres of chromosomes
(Easiest stage to observe chromosomes)
Process of Anaphase
- Spindle fibres contract and the centromeres are pulled in the opposite direction
(Chromosomes split to chromatids) - Cell elongates
Process of telophase
- Nuclear membrane reforms around two sets of chromosomes
- Spindle fibre disappears
- Chromosomes become longer, thinner and uncondense
- Cytokinesis begins during telophase
Process of Cytokinesis
- Cytoplasm divides and separates into two daughter cells
How does cytokinesis occur in animal cells?
Cell membrane moves inwards and pinches the two daughter cells apart
How does cytokinesis occur in plant and fungi cells?
New membrane and cell wall forms between two daughter nuclei
What are some places mitosis occurs in humans?
Bone marrow, epithelia tissue e.g. skin, hair etc.
What is the apical meristem?
Usually the shoot/tip and the root tip (provides height growth)
What is the lateral meristem?
Occurs in the cambium of the shoot/trunk (provides secondary growth, width)
What are some places mitosis occurs in plants?
Occurs in the meristem of the plant (lateral and apical meristem)
What is meiosis?
Responsible for producing gametes (sperm and egg)
How many daughter cells does meiosis produce?
4 non-identical daughter cells
Note: All daughter cells are haploid
How many stages does Meiosis have?
PMAT (I)
PMAT (II)
What is the purpose of meiosis I?
To reduce the number of chromosomes. The sister chromatids are still joined together at this stage
What is the process/purpose of Prophase I?
- Chromosomes condense and thicken
- Nuclear envelope disappears
- Centrioles and spindle fibres form
- Chromosomes pair up in homologous pairs
- Physical crossing over occurs causing random swapping of genetic information in the homologous pair
Does Metaphase I remain the same as Mitosis?
Yes, it remains the same
What is the process/purpose of Anaphase I?
Chromosomes move away from each other and the pair is separated, but chromatids remain stuck together
Note: Only the homologous pairs are separated (main difference to mitosis)
What is the process/purpose of Telophase I?
- Spindle fibre disappears
- Nuclear envelope forms around each set of chromosomes
Note: Cells do not condense the chromosomes as Meiosis II begins quickly after - Cytokinesis also occurs
What are the differences between Meiosis I and II?
- Chromosomes aren’t duplicated
- Like in mitosis, the sister chromatids separate
What does DNA mean?
Deoxyribonucleic acid
What is DNA?
Hereditary genetic information is carried in the form of genes. It contains chromosomes in the nuclei of cells
What is the structure of DNA?
- Sugar phosphate backbone
- Nitrogenous Bases
- Double-stranded helix
- Anti-parallel
- Made up of nucleotides joined together
Based pairing (AT, CG)
What is the structure of RNA?
- Another type of nucleic acid
- Single-stranded
Who announced the discovery of DNA in 1953?
Watson and Crick, built the model/structure based off other discoveries and work
What are the 4 nucleotides in DNA?
Adenine (A) + Thymine (T)
Guanine (G) + Cytosine (C)
In what direction do the nucleotides run?
5’ to 3’
What is RNA?
Similar to DNA, it has a role in polypeptide synthesis.
What is the difference between DNA and RNA?
- Exists as a single strand
- Strands are shorter
- Sugar phosphate backbone, has ribose sugar instead of deoxyribose
- T in DNA is replaced by Uracil (U)
Can the appearance of chromosomes change depending on the stage of the cell cycle?
Yes.
What do chromosomes in eukaryotes look like?
Sets of linear chromosomes
What do chromosomes in prokaryotes look like?
Single circular chromosomes.
What are histones and how do they relate to DNA?
Chromosomes are made up of DNA but also small structural proteins called histones. DNA is wound around the histones, forming structures called nucleosomes.
Is DNA replication called semi-conservative? What does this term mean?
Yes. Semi-conservative due to half of the new strand coming from the original strand
General Overview of the DNA replication:
- Original DNA unzips
- Free nucleotides are added to the original pairs according to base-pair rule
- Two new DNA molecules are separated
What are the two types of strands in DNA replication?
Leading and lagging strand
Which way does the template/leading strand go?
5’ to 3’
Which way does the lagging strand go from?
3’ to 5’
What is the function of DNA helicase?
Unzips/opens the DNA double helix
What is the function of DNA polymerase?
Matches and adds new nucleotides to form daughter DNA strand
What is the function of primase?
Forms DNA Primer
What purpose does RNA primer serve?
Serves as the starting point for the DNA polymerase to begin adding the new nucleotides
What is the function of DNA ligase?
Joining together of Okazaki fragments on the lagging strand
General overview of DNA replication (including the special enzymes)?
- helicase unzips the double helix
- primase adds rna primer for the dna polymerase to work
- dna polymerase adds nucleotides from 5’ to 3’ on the leading strand
- okazaki fragments are added and the dna polymerase works backwords in fragments form 5’ to 3’
- dna polymerase removes rna primers and replaces it
- dna ligase joins the strands together
What is the replication fork formation?
Begins at specific part of DNA and specialised proteins open up the DNA forming two replication forks. It forms a replication bubble. DNA helicase is responsible for the unwinding.
What is Primer Building?
Primase makes RNA primer allowing for a starting point. DNA polymerase adds nucleotide to 3’ end of primer, building new DNA strand from the template strand.
Note: DNA polymerase only makes from 5’ to 3’
What directions does DNA polymerase run?
Runs from 5’ to 3’.
Leading strand is 5’ - 3’ and lagging strand is 3’ - 5’.
Antiparallel, so the leading strand is ‘easy’ as it runs from 5’ to 3’ continuously.
Lagging strand is made in segments 5’ to 3’.
What is elongation?
Fork moves forward and causes the DNA polymerase to come off and reattach to newly exposed DNA. Lagging strand is made this way, primers are continuously added, called Okazaki fragments.
What is termination?
DNA Polymerase I (exonuclease) removes all RNA primer from original strands, replacing them with appropriate bases. The exonuclease reads, proof-checks the DNA and DNA ligase joins Okazaki fragments together. Telomere act as protective cap and prevent nearby chromosomes from fusing.
Summary of DNA Replication
- DNA is unzipped by DNA helicase
- RNA Primase adds RNA primer
- DNA polymerase builds DNA strand from 3’ end of primer (5’ - 3’) by adding bases according to the base pair rule. This is where an error occurs wrong base/s paired up
- Once all bases are done, RNA primer is replaced by DNA and DNA ligase, joins all sectors together
What is meiosis’ relation to genetic variation?
Meiosis creates new genetic combination and new genetic interactions. Increases genetic diversity of species and is important to species survival.
How is DNA held in Prokaryotes?
Have chromosomal DNA but it is not held within a nucleus
How is DNA held within Eukaryotes?
Held in a nucleus
Information about Prokaryotic DNA:
- One double stranded piece of circular DNA
- Has some ribosomes used for protein synthesis
- DNA is circular, meaning it doesn’t have telomeres
- Less condensed than eukaryotes
Information about eukaryotic DNA?
- More complex than prokaryotic cells
- Has internal membranes around organelles
- DNA packaged with histones and exist in linear structures (chromosomes)
