1 cell cycle + mitosis exam qs

describe binary fission in bacteria

• replication of circular DNA and plasmids

• division of cytoplasm to produce daughter cells

• each with a single copy of circular DNA

• and variable number of copies of plasmids

explain why preventing formation of spindle fibres stops the cell cycle

centromeres can’t attach to spindle so no metaphase

when observing an onion root, why did the student only use the 5mm at the tip?

because thats where dividing cells are found/mitosis occurs

when observing an onion root, why did the student press down firmly on the cover slip

thin layer of cells so light can pass through

what is the name given to the division of the cytoplasm during the cell cycle

cytokinesis

describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

examine many cells to ensure a representative sample

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope. Suggest how this procedure moved the chromosomes apart.

Water moves into the cytoplasm by mitosis so cell gets bigger

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance. Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.

differences in base sequences

What is a homologous pair of chromosomes?

2 chromosomes that carry the same genes

name the process by which bacterial cells divide

binary fission

“Push down hard on the cover slip, but do not push the cover slip sideways.” Explain why the student was given this instruction

push hard to squash tissue, don’t push sideways to avoid rolling cells together

When does interphase occur?

Before mitosis

What does interphase look like?

Nucleus appears spherical and is surrounded by a nuclear envelope

What happens during interphase?

Cell growth, DNA + organelle replication

What is the order of the 5 stages of mitosis?

Prophase, metaphase, anaphase, telophase, cytokenesis

what is a chromatid

each of a pair of identical DNA molecules after DNA replication, joined at the centromere

chromatin

protein/dna complex making the chromosome

chromosomes

molecules of DNA complexed with specific proteins responsible in eukaryotes for storage + transmission of genetic information

what are histones

5 kinds of proteins forming complexes with eukaryotic DNA

cytokinesis in plant cells (4)

• Spindle fibres don’t disappear- form phragmoplasts.

• many organelles congregate in this area + some fluid filled vesicles budded off from golgi apparatus containing material needed to build new cellulose cell wall.

• vesicles join to form cell plate which grows across middle, eventually separating the 2 daughter cells

• in certain regions vesicles don’t fully form, forms cytoplasmic connection = plasmodesma

how can uncontrolled cell division cause cancer

Mitosis + the cell cycle are controlled by genes. Normally when cells have divided enough times to make enough new cells, they stop, but if there’s a mutation in a gene that controls cell division, the cells can grow out of control. The cells keep dividing to make new cells which forms a tumour. Cancer is a tumour that invades surrounding tissue.

What does cancer treatment often involve

Killing dividing cells by blocking part of the cell cycle, which prevents growth of tumours

What 2 things can chemotherapy be

Inhibiting enzymes needed for DNA replication so cell can’t enter synthesis phase. Inhibit metaphase by disrupting spindle formation

what is g1

gap phase 1- cell grows and new organelles and proteins are made

what is S

Synthesis- cell replicates its DNA, ready to divide by mitosis

what is g2

Gap phase 2- cell keeps growing and proteins needed for cell division are made

what is mitosis

the process by which identical body cells are produced for: growth e.g. tissues/embryo, replacing damaged or old cells, asexual reproduction in some organisms

what happens in prophase (4)

• chromosomes start to condense + spindle starts to form

• chromosomes become visible, each divided into identical chromatids held by centromeres.

• nuclear envelope breaks down and nucleolus disappears.

• spindle fibres develop from centrioles at poles + attach to centromeres

what happens in metaphase

Chromosomes align at centre of cell, aka metaphase plate. Chromosomes attached to spindle fibres by their centromeres

what happens in anaphase

spindle fibres shorten to pull sister chromatids to opposite poles of cell. results in separation of the chromatids to form 2 daughter chromosomes. energy provided by mitochondria.

what happens in telophase

chromosomes begin to lengthen + in doing so appear indistinct. spindle fibres disintegrate. separate nuclear envelopes and nuclei reappear so their movement is complete.

what happens in cytokenesis

Follows telophase. Other organelles e.g. ribosomes + mitochondria become evenly distributed around each nucleus + cytoplasm begins to divide.

What is the splitting of the cytoplasm in cytokinesis called in animal cells?

Cleavage

describe and explain what the student must have done when counting cells to make sure the mitotic index he obtained for the root tip was accurate

more detail, e.g. large number to produce a more representative sample

what is this

interphase

what is this

prophase

what is this

metaphase

what is this

anaphase

what is this

telophase