the cell cycle

what does replication of a DNA molecule begin with

the double helix partially unwinds

as it does what breaks down

the hydrogen bonds between complementary base pairs break down

what enzyme is involved in breaking the hydrogen bond

DNA helicase

what does the break down of hydrogen bonds between complementary base pairs allow the two polynucleotide strands to do

to move apart

what is the point at which they are separated called

the replication fork

what do we now have

two separate strands of nucleotides with unpaired bases exposed to free nucleotides

what can we find in the nucleus

individual DNA nucleotides

what are these nucleotides attracted to

the exposed bases on each polynucleotide strand

what now forms

hydrogen bonds between complementary bases

as a result of this what does each of the polynucleotide strands of DNA soon build up

a complementary sequence of nucleotides

what are the original strands known as

template strands

why is this

because each of the original strands are acting as a pattern for the assembly of a new strand

what forms between the nucleotides

phosphodiester bonds

by what reaction does this happen

condensation reactions

what enzyme is this linking of DNA nucleotides controlled by

DNA polymerase

how many new DNA molecules do we end up with

2

what type of replication is this called

semi-conservative replication

what is meant by semi-conservative replication

one original strand remains intact and one new complementary strand is made using the old strand as a template

what do the DNA molecules now do to complete the process

they rewind

go over semi conservative

accoriding to cell thoery how do all cells arise

all cells arise from previously existing cells by cell division

what is mitosis

a type of cell division that occurs in eukaryotic cells

what happens during mitosis

a parent cell divides to form two daughter cells

what do each of the daughter cells contain

some of the cytoplasm from the parent cell

what they also contain

a compete copy of the parent cell’s DNA

what does that make them to each other and to the parent cell

genetically identical

what is the DNA in eukaryotic cells contain in

linear chromosomes

describe the appearance of the chromosome before DNA replication

it is a single rod-like structure containing only one tightly wound double helix of DNA

what does DNA replication give rise to

two rod like structures each containing identical molecules of DNA

what is a centromere

the structure in a chromosome that holds together chromatids until they are separated by spindle fibres

how do we describe chromatids in a pair

sister chromatids

during mitosis what happens to the sister chromatids

they are separated

what happens during interphase

cells makes copy of its chromosomes involving DNA replication cell grows

what happens during prophase

chromosomes coil ,becoming shorter and fatter we can now see them with an optical microscope nuclear envelope disappears. protein fibres for a spindle in the cell . each chromosome contains two chromatids each containing an identical DNA molecule form DNA replication

what happens during metaphase

one or more spindle fibres attaches to the centromere of each chromosome. chromosomes line up in the middle

what happens during anaphase

centromere holding each pair of sister chromatids togetehr divide and spindle fibres shorten and pull one of each pair of sister chromatids to opposite piles of the cell. we can now refer to chromatids as chromosomes

what happens during telophase

the two sets of separated chromosomes collect at opposite ends of the cell a new nuclear envelope forms around each set of chromosomes. chromosomes become long and thin we can no linger see them clearly with an optical microscope .cytoplasm divides to form two new cells (cytokineis)

how does cytokinesis happen in animal cells

the cell membrane is pulled inwards across the centre of the cell pinching off the cytoplasm into two equal halves each containing a new nucleus

how does cytokinesis happen in plant cells

vesicles fuse to extend the cell membranes across the cytoplasm and then new cell walls develop between them

are all cells able to divide

no

what must the new cells do before they are able to replicate their DNA and and divide by mitosis

they must grow

what is formed

a cycle

what is this cycle called

the cell cycle

what happens during the g1 phase

the cell increases in size

what happens during the S phase

the cell replicates its DNA

what happens in the G2 phase

the cell increases further in size and replicates its cell organelles

what do prokaryotes not have

chromosomes

what is their DNA enclosed in

a single circular DNA molecule

what is also replicated in prokaryotes

plasmids

how many plasmids can a bacteria contain at any given time

more than one copy

what is regulated

the maximum number of copies of a plasmid a bacteria can have

what is cell division in prokaryotes called

binary fission

outline binary fission

the circular DNA molecule and any plasmids in the cell undergo DNA replication the cell then divides into two cells each containing roughly half of the cytoplasm one copy of the circular DNA molecule and some of the plasmid copies

what do prokaryotes lack

they have no membrane bound organelles no nuclear envelope to break down and there are no spindle fibres

even though there are no spindle fibres involved in binary fission what is put in place

mechanisms to ensure that a copy of the single circular DNA molecule and some copies of each plasmid are in each half of the bacterial cell before division takes place

how can a daughter cell die during binary fission

by not getting a single copy of a plasmid

what properties would we say that viruses have

they are acelluar and non living

what is meant by acellular

they do not have a cell structure and consist only of DNA or RNA surrounded by a protein coat

what does this mean they do not carry out

cell division

how do viruses replicate

they inject their nucleic acid into a host cell

once the nucleic acid is inside a host cell what does the host cell do

the host cells DNA replicating and protein synthesising systems make more viruse particles

what eventually happen to these viruses copies

they are released

what are the two ways in which these copies can be released

when the whole host cell bursts or by budding one at a time through the host cell memebrane

do all eukaryotic cells undergo the cell cycle

no

as most cells mature what do they lose the ability to do

divide

what is differentiation

newly formed cells changing their properties when they become specialised for specific functions

what do cells differentiate to form

a tissue with perform the same function

during differentiation what do most human cells lose the ability to do

divide by mitosis

what are two ways in which cells control their own division and thus numbers

differentiation and programmed cell death

what can sometimes happen to these mechanisms

they can break down

what is the result of this

uncontrolled cell division

what is a large mass of these cells called

a tumour

what may tumours become

cancerous

when does cancer occur

if cells from a tumour are able to break away and form secondary tumours elsewhere