Topic 3 Flashcards
what is a eukaryotic cell
cells that contain a nucleus and organelles enclosed by a plasma membrane
what is a prokaryotic cell
A type of cell that does not contain any membrane bound
organelles or a nucleus
what organelles have a double membrane
nucleus, mitochondria and chloroplasts
what is the rough endoplasmic reticulum
system of interconnected membrane-bound, flattened sacs that have ribosomes attached to the outer surfaces
proteins that are made on these ribosomes are transported through the ER to other parts of the cell
what are ribosomes
organelles made up of ribosomal RNA and protein
are found free in the cytoplasm or attached to the endoplasmic reticulum and are the site of protein synthesis
what are lysosomes
spherical sacs containing digestive enzymes and bound by a single membrane
involved in breakdown of unwanted structures/destruction of whole cells when old ones need to be replaced/during development.
acrosome is a specialised lysosome
what is the smooth endoplasmic reticulum
makes lipids and steroid
similar to rER but has no ribosomes attached
what is the golgi apparatus
stacks of flattened, membrane-bound sacs formed by the fusion of vesicles from the ER
modifies and packages proteins into vesicles for transport
what are centrioles
hollow cylinders made up o 9 protein microtubules
involved in formation of the spindle during nuclear division and in transport within cell cytoplasm
describe the production of proteins and their route through the cell
- transcription of DNA to mRNA
- mRNA leaves nucleus
- proteins made on ribosomes enter the rough ER
- protein moves through the ER, assuming 3D shape
- vesicles pinched off the rough ER contain the protein
- vesicles from the rER fuse to form the flattened sacs of the Golgi apparatus
- proteins are modified within the Golgi
- vesicles pinched off the Golgi apparatus contain modified protein
- vesicles fuses with cell surface membrane releasing the protein such as extracellular enzymes
define features of an egg cell
incapable of independent movement
wafted by ciliated cells along fallopian tube
cytoplasm contains lots of protein and lipid food reserves for a developing embryo
has a coating = zona pellucida
define features of the sperm
has a flagellum enabling it to swim
large reserve of mitochondria
describe steps of fertilisation
- sperm reach ovum
- chemicals released from ells surrounding ovum to trigger acrosome reaction
- acrosome swells and fuses with sperm cell membrane membrane
- digestive enzymes in acrosome are released.
- enzymes digest through the follicle cell and the zona pellucida surrounding ovum
- sperm fuses with the ovum membrane and the sperm nucleus enter ovum
- enzymes released from lysosomes in ovum to thicken zona pellucida to prevent other sperm entry
- nuclei of sperm and ovum fuse
what kind of nucleus do sperm have
haploid
to ensure a full set of chromosomes at fertilisation
what is the cortical reaction
when the lysosomes release enzymes to harden the zona pellucida
what is a locus
the fixed point on a chromosome occupied by a gene
explain how shortening the spindle fibres affects mitosis
sister chromatids cannot be separated
mitosis will stop at metaphase
daughter cells are produced with incorrect numbers of chromosomes
explain each stage of the cell cycle
- Interphase: new organelles synthesised and DNA replication occurs
- Mitosis
a) Prophase: chromosomes condense and chromatids become visible; spindle starts to form from centrioles; spindle fibres start to form and the equator is established
b) Metaphase: chromosomes’ centromeres attach to the spindle fibres at the equator
c) Anaphase: centromeres split; spindle fibres shorten; pulling each half of each centromere towards each pole; ends when separated chromatids reach the poles and spindle breaks down
d) Telophase: chromosomes unravel, nuclei form and the two separate sets of info become enclosed in each - Cytokinesis: ring of protein filaments bound to inside of surface cell membrane contract until cell as split into two
how is DNA folded from its double helix to a chromosome
is wound around histone proteins
they then coil to form chromatin fibres
chromatin fibre attaches to a protein scaffold forming loops
folding the protein scaffolding produces the condensed chromosome structure seen during nuclear division
what is the process of meiosis
- chromosomes replicate before division, after replication, each chromosome is made up of 2 strands of genetic material: 2 chromatids
- homologous chromosomes pair up and then separate
- they then separate again
what is the cell surface membrane
phospholipid bilayer containing proteins and other molecules forming a partially permeable membrane
what is a mitochondrion
the inner of its 2 membranes is folded to form projections - cristae
site of later stages of respiration
what is the nucleus
enclosed by a envelope of 2 membranes which is perforated by pore
contains chromosomes an nucleolus
chromosomes are made of DNA and contain genes that control the synthesis of protein
what is independent assortment
when homologous chromosomes align
randomly and separate
ensures genetic diversity in gametes
what is a homologous chromosome pair
chromosome pairs of approximately the same length, centromere position and staining pattern for genes with the same corresponding loci
what is a chromatid
one of the 2 identical halves of a chromosome that has been replicated in preparation in cell division
what is a chromatin
mass of genetic material that is composed of DNA and proteins that condense to chromosomes during eukaryotic cell division
what is “crossing over”
exchange of genetic material between non-sister chromatids of homologous chromosomes
what are sister chromatids
2 identical copies of the same chromosome formed by DNA replication
how are sister chromatids attached
by a centromere
in crossing over
what is the name given to the points of contact between a homologous pair of chromosomes
chiasmata
what happens during interphase
new organelles are synthesised and DNA replication occurs
what happens during mitosis
prophase: chromosomes condense and microtubules from cytoplasm form a spindle and establish a cell equator
breakdown of nuclear envelope signals end of prophase
Metaphase: spindle fibres attach to centromeres
Anaphase: spindle fibres shorten, pulling 2 halves of centromeres in opposite directions, one chromatid to each end of cell
Telophase: chromosome unravels, nuclear envelope reforms, each set of genetic info enclosed in separate nuclei
what happens in cytokinesis
it is thought that: ring of protein filaments bound to inside surface of cell surface membrane contract until cell divides
myosin and actin responsible
Plant cells synthesise a new cell plate between the 2 new cells
how does meiosis result in genetic variation
shuffling of existing genetic material into new combinations during meiosis
including independent assortment and crossing over
what happens during prophase 1 in meiosis
crhomosoems condense
pairs oh HOMOLOGOUS chromosomes line up closely together
1 centriole from each cell moves towards opposite poles of the cell
nuclear membrane break down
describe and explain what happens during anaphase
sister chromatids separate
they move to opposite poles of the cell
why is a stain used in mitosis experiment
to make DNA/genetic material visible
why is mitosis important in the life of an organism
growth/increase in cell number
replace cells/ repair tissues/organs/body
genetically identical daughter cells
asexual reproduction
describe what happens in
a) metaphase
b) anaphase
a) spindle is formed and chromosomes line up on the equator
b) chromosomes separate and are pulled apart to opposite poles of the cell
why is it advantageous for cells to complete cell cycle in a short time
cells can be replaced quickly
why might a drug that inhibits DNA polymerase be effective against cancer
prevents DNA from being replicated so new cells cannot be formed
why do you put the plant roots in acid
to stop mitosis; to separate cells; to hydrolyse the cell wall; to allow stain to into the cell; allows cells to be more easily squashed
what precautions must you take when handling hydrochloric acid
eye protection
add water to spills immediately
gloves worn
do not pour away down the sink
a student compares mitotic index in the roots of 2 different species
what should they take into consideration
roots/plants of the same age
same distance from root tip
same pressure when squashing them
same growing conditions
same amount of time in acid
picked at same time of day
describe appearance and behaviour of chromosomes
chromosomes condense and become visible
chromosomes appear as 2 sister chromatids joined at the centre by a centromere
chromosomes line up at equator
attach to spindle fibres by the centromeres
centromere splits
chromosomes pulled to opposite poles
chromosomes uncoil
describe and explain the processes that occur during meiosis that increase genetic variation
homologous chromosomes pair up
independent assortment
maternal and paternal chromosomes are shuffled into random combinations
crossing over leads to exchange of parts of alleles between homologous chromosomes
both create new combinations of alleles
describe the role of the centromere in mitosis
holds the chromosomes together; attaches to the spindle; allows the chromatids to be separated
describe 2 events during interphase which prepare a cell for mitosis
DNA Replication
protein synthesis
increase in cytoplasm
replication of organelles
describe the behaviour of chromosomes during mitosis and explain how this results in the production of 2 genetically identical cells
chromosomes thicken and shorten
chromosomes are made up of 2 identical chromatids due to replication
chromosomes move to the equator and attach to individual spindle fibres
spindle fibres contract and centromeres divide
chromosomes separate and move to opposite directions/poles
each pole receives identical copies of each chromosome
nuclear envelope forms around each group of chromosomes at each pole
explain why meiosis is important in sexual reproduction, apart from producing gametes are genetically different
produces haploid cells
fertilisation maintains diploid
what is a totipotent stem cell
a stem cell that can differentiate into all other types of cell
what is a pluripotent stem cell
a stem cell that can differentiate into most other types of cell
what is a multipotent stem cell
a stem cell that can differentiate into some other types of cell
what is a blastocyst
a hollow ball of cells formed 5 days after conception
outer layer goes on to form the placenta
what is the epigenome
chemical markers that attach to histone proteins
role is to influence which genes are transcribed in a particular cell
what does methylation of DNA do
attaches to cytosine of DNA and causes the nucleosomes to pack together tightly
prevents transcription factors from binding to DNA and the genes are not expressed
what does acetylation of DNA do
attaches to the histone proteins and results in the DNA being loosely packed
transcription factors can bind to DNA and the genes can be expressed
why are cells of the pancreas all the same even after division
during DNA replication, epigenetic markers are copied with the DNA so when the cells divide, it forms a cell with the same markers
what do epigenetics do
involve changes in gene function without changing the base seqence
what is the promoter region
a region of DNA where RNA polymerase begins to transcribe a gene
what is a gene repressor and how does it work
it attaches to the operator gene and switches the gene off as it blocks the attachment site where RNA polymerase attaches to the promotor region
what is the operon
the operator and genes associated
explain how cells differentiate to become specialised tissues
signals/ stimulus cause some genes to be activated
only activated genes are transcribed and mRNA is synthesised
mRNA leads to the synthesis of specific proteins
cell structure is then determined
what do chemical signals do
causes certain genes to be activated
only the activated genes are transcribed and mRNA synthesised
synthesis leads to specific proteins being made which causes cell modification
what is a gene regulatory proteins
any protein that influences DNA through activation and repression
what are activators
transcription factors that increase the rate of transcription
they work by helping RNA polymerase to bind to the start of a gene and to begin transcription of that gene
what are repressors
transcription factors decrease the rate of transcription
they work by stopping RNA polymerase from binding to the DNA at the start of the gene, inhibiting transcription of that gene
what do eukaryotes use to control gene expression
transcription factors
what is a transcription factor
a protein that controls the transcription of genes by binding by a specific region of the DNA
they ensure that genes are being expressed in the correct cells, at the correct time and at the right level
describe how pluripotent cells become specialised
stimulus
some genes are active
active genes are transcribed to mRNA
mRNA translated to produce protein
protein determines cell structure and function
explain how a bone marrow cell can give rise to red blood cells
by differentiation
due to certain stimuli
which causes some genes to be deactivated
mRNA produced from active genes
removal of nucleus/ produces a bio concave shape
explain how groups of specialised cells can produce the same enzyme
genes can be activated/ deactivated
cells receive the same stimulus
all these cells have the same gene for the enzyme activated
resulting in production of mRNA for the enzyme
define polygenic
a characteristic showing continuous variation caused by multiple genes at different loci
Explain how epigenetic changes affect the development of tissues in the embryo.
DNA is wrapped around histones
modification/ acetylation of histone affects binding of RNA polymerase
methylation of DNA affects transcription of genes
therefore gene expression is altered
They have a mutation in a gene coding for a protein in the cell membrane.
Deduce why this mutation makes these people resistant to HIV infection.
the protein is a receptor that HIV attaches to
viral RNA cannot enter cell
give a difference between a tissue and an organ
a tissue is made of one type of cell whereas an organ is made up of different tissues
Describe the decisions that society has to make about the use of these embryonic stem cells.
embryonic stem cells are totipotent and can be used in a wider range of treatment
source of embryonic stem cells has to be regulated/considered
moral/ethical issues as use of embryonic stem cells destroys embryos
need for research establishments to be regulated
Give the meaning of the term totipotent cell.
a cell that has the ability to differentiate into all types of cell
Describe how cells become specialised.
chemical signals some genes to be switched on
only activated genes are transcribed
mRNA leads to synthesis of specific proteins which cause cell modifications
Explain why stem cells from the heart cannot be used to grow cells to repair the cornea.
cell not totipotent
therefore some genes have already been activated/ deactivated
therefore will not be able to specialize into cornea cells
Explain why chemicals from the eye are needed to produce corneal cells from a suitable source of stem cells.
chemicals cause some genes to be switched on
genes are transcribed producing specific mRNA
specific mRNA are translated into specific proteins
these proteins cause the cell to develop into corneal cell
State what is meant by the term stem cell
a cell that is undifferentiated
that can give rise to specialised cells
that can divide to produce more stem cells
Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells.
both increase number of cells
mitosis produces diploid cells, meiosis produces haploid cells
meiosis produces genetically different daughter cells, mitosis produces genetically identical daughter cells
mitosis produces 4 sperm cells, meiosis produces 8 sperm cells
Explain what is meant by the term sex-linked disorder.
disorder caused by mutated gene on the X/Y chromosome
therefore disorder is more likely in one gender than the other
Epigenetic changes can cause monozygotic twins to have different body masses.
Explain how epigenetic changes can cause differences in a characteristic.
histone modification/ DNA methylation
affects activation of genes
affecting metabolism
Explain how epigenetic changes affect the activation of genes in daughter cells
genes are deactivated because of DNA methylation
the same genes will be activated in the daughter cells
Explain why an individual may have a greater adult height than their biological parents
height is affected by the environment as well as the genotype
height is an example of polygenic inheritance
offspring can inherit a mixture of alleles from both parents
could have a higher protein diet
Describe how a tissue differs in structure from a system.
tissue contains one type of cell
system contains different tissues/organs
Describe how mesenchymal stem cells can give rise to different types of cell
different stimuli activate different genes
genes activated are transcribed
mRNA translated to produce proteins
proteins determine structure/function of cells
different genes activated result in different types of cell being produced
The function of TET is to remove methyl groups from DNA.
Explain how a mutation in the gene for succinate dehydrogenase can increase the risk of developing cancer.
mutation is a change in the base sequence in gene/ DNA
succinate dehydrogenase less/non- functional
succinate then accumulates
accumulation inhibits TET
therefore methyl groups are not removed
affects gene transcription
greater methylation of DNA is associated with increased cancer risk
Explain how epigenetic events might be involved in regulating collagen synthesis in rats given alcohol.
exposure to alcohol may result in changes of methylation of DNA
so that collagen gene is more likely to be activated
define continuous variation
A type of variation within a population produced by polygenic
inheritance where the phenotypes are spread over a range of values.
define differential gene expression
the switching on or off of genes o control functions within a cell by varying the production of proteins.
what is the lac operon
A group of genes that control lactose uptake and metabolism in certain types of
bacteria and are all regulated by the binding of the lac repressor to the lac operator.
575 identified mutations to the F9 gene that cause severe symptoms of
haemophilia.
The same percentage of these types of mutation is found in the F8 gene.
Calculate the number of mutations to the F8 gene that produce severe symptoms.
575/1133 = 0.5075/0.51
2931 x 0.51 = 1495
Devise an investigation to determine the effect of exposure time to Agil on the rate of mitosis in onion root tips.
controlled conc of Agil
control temperature
roots exposed to agil for a range of different times
macerate roots
use toluidine blue stain
count number of cells undergoing mitosis
explain how crossing over may differ in sex chromosomes
crossovers cannot form between the X and Y chromosome
because they are not homologous chromosomes
Explain why DNA is replicated before mitosis begins
to ensure that the daughter cell has a diploid number of chromosomes
ensures that they are genetically identical
Explain how large numbers of cells with the same phenotype can be produced in a tissue
mitosis produces genetically identical cells
phenotype is determined by genotype and the effect of environment
explain why the nucleus cannot be observed at the end of prophase in eukaryotic cells
nuclear envelope has broken down
DNA is condensed into individual chromosomes
describe how each gamete receives only 1 allele of each gene
homologous chromosomes are separated from one another
sister chromatids are also separated from one another
spindle fibres pull chromatids to opposite poles of the cell
describe the events that occur during prophase
nuclear envelope breaks down
chromosomes condense
spindle + spindle fibres form
what is the purpose of the cortical reaction
to ensure that only 1 sperm fertilises the egg
give a reason for the high density of mitochondria found in the midpiece of a sperm cell
energy/ ATP for the movement of flagellum/ swim
