All cells arise from other cells Flashcards
Cells revisions
State what cell cycle is and outline its stages
Cycle of division with intermediate growth periods
- Interphase
- Mitosis or meiosis (nuclear division)
- Cytokinesis (cytoplasmic division)
Explain why cell cycle does not occur in some cells
After differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have the ability to divide
Outline what happens during interphase
G1: cell synthesises proteins for replication e.g. tubulin for spindle fibres & cell size doubles
S: DNA replicates = chromosomes consists of 2 sister chromatids joined at a centromere
G2: organelles divide
What happens during prophase (1st phase)
- Chromosomes condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere)
- Centrioles move to opposite poles of cell (animal cells) & mitotic spindle fibres form
- Nuclear envelope & nucleolus break down = chromosomes free in cytoplasm
What happens during metaphase (2nd phase)
Sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres
What happens during anaphase
required energy from ATP hydrolysis
- Spindle fibres contract = centromeres divide.
- Sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of cell
- Spindle fibres break down
What happens during telophase
- Chromosomes decondense, becoming invisible again
- New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome
Explain procedure for root tip squash experiment
- Prepare a temporary mount of root tissue
- Focus an optical microscope on the slide. Count total no. of cells in field of view & no. of cells in a stage of mitosis
- Calculate mitotic index (proportion of cells undergoing mitosis)
Explain how to prepare temporary root tip mount
- Place root in hydrochloric acid to halt cell division & hydrolyse middle lamella
- Stain root tip with a dye that binds to chromosomes
- Macerate tissue in water using mounted needle
- Use mounted needle at 45 degrees to press down coverslip & obtain single layer of cells. Avoid tapping air bubbles.
What are tumour suppressor genes?
Genes that code for proteins to trigger apoptosis (progammed death of damaged cells)/ slow cell cycle
What are proto-oncogenes?
Genes that code for proteins to stimulate cell cycle to progress from one stage to the next
How can mutation to tumour suppressor genes & proto-oncogenes cause cancer?
- Tumour suppressor: no production of a protein needed to slow cell cycle
- Proto-oncogenes: form permanently - activated oncogenes
- Disruption to cell cycle -> uncontrolled cell division -> tumour
Suggest how cancer treatments control rate of cell division
Disrupt cell cycle
- prevent DNA replication
- disrupt spindle formation = inhibit metaphase/ anaphase
(can also damage healthy cells)
How do prokaryotic cells replicate?
Binary Fission:
- DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm.
- Cell elongates, separating 2 DNA loops
- Cell membrane contracts & septum forms
- Cell splits into 2 identical progeny cells, each with 1 copy of DNA loop but a variable number of plasmids
Why are viruses classified as non-living?
Are acellular: no cytoplasm, no metabolism & cannot self-replicate
Outline how viruses replicate
- Attachment proteins attach to receptors on host cell membrane
- Enveloped viruses fuse with cell membrane or move in via endocytosis & release DNA/ RNA into cytoplasm OR viruses inject DNA/ RNA
- Host cell uses viral genetic info to synthesise new viral proteins/ nucleic acid
- Components of new viral particle assemble
How do new viral particles leave host cell?
a) Bud off & use cell membrane to form envelope
b) Cause lysis of host cell
Why is it difficult to develop effective treatments against viruses?
Replicate inside living cells = difficult to kill them without killing host cells
