topic 3 Flashcards
what structures are always present in prokaryotic cells (5)
plasmid circular dna cell surface membrane cell wall cytoplasm
what discrete, membrane bound organelles do eukaryotic cells contain
- nuclei
- mitochondria
- chloroplasts (plants only)
differences: eukaryotic and prokaryotic cells
eukaryotic bigger
not all eukaryotic cells have a cell wall
lysosome
spherical sacks containing digestive enzymes, bound by a single membrane
Breakdown of unwanted structures within a cell and whole cell destruction when old cells replaced/ during development.
Smooth endoplasmic reticulum
makes lipids and steroids eg. reproductive hormones
rER
system of interconnected membrane bound flattened sacks
Ribosomes attached to outer surface
Proteins made on these ribosomes are transported through the ER to other parts of the cell
Mitochondrion
Inner of 2 membranes folded to form cristae.
Site of later stages of aerobic respiration
Golgi apparatus
stacks of flattened membrane bound sacs formed by fusion of vesicles from the ER.
Modifies and packages proteins in vesicles for transport
Protein production and route through cell
- Transcription of DNA to mRNA
- mRNA leaves nucleus
- Proteins made on ribosomes enter rER
- Protein moves through ER, assuming 3D shape en route.
- Vesicle pinched off rER contain the protein
- Vesicles from rER fuse to form flattened sacs of Golgi apparatus
- Proteins modified within Golgi apparatus
- Vesicle pinched off Golgi apparatus contain the modified proteins
- Vesicle fuses with cell surface membrane, releasing protein such as extracellular enzymes.
2 mammal gametes
ovum
sperm
adaptations of ovum (5)
large cell
not capable of independent movement
wafted along one of the oviducts from ovary to uterus by ciliated cells lining the tubes and muscular contraction of tubes
cytoplasm of ovum contains protein and lipid food reserves for a developing embryo
‘zona pellucida’: jelly like coating surrounding the cell
sperm adaptations
smaller
motile
flagellum powered by mitochondria energy release enables swimming
continually produced once maturity
enter vagina through intercourse + swim through uterus. Passage assisted by muscular contractions of walls
If intercourse during ovulation, sperm meet ovum in oviduct
Sperm attached to ovum by chemicals released by it
Intercourse🍆💦
- sperm reaches ovum
- chemicals released from the cells surrounding the ovum, triggering ACROSOME REACTION
- Acrosome swells, fusing with sperm cell surface membrane
- Digestive enzymes in acrosome released
- enzymes digest through follicle cells
- …..and zona pelucidia surrounding ovum
- sperm fuses with ovum membrane
- Sperm enters ovum
- enzymes released from lysosomes in ovum thicken the jelly like layer; preventing entry of other sperm
- Nuclei of ovum and sperm fuse
what are gametes
HAPLOID
23 chromosomes made up of one of each homologous pair and one sex chromosome
fuse to make a zygote (46 chromosomes)
what is mitosis
type of cell division
Produces new body cells as an organism grows and develops
Retains the full (diploid) number of chromosomes
what is meiosis
produces gametes haploid number of chromosomes occurs in ovaries//testes ovaries of flowering plants creates genetic variation
how does meiosis shuffle existing genetic material
crossing over
independent assortment
what is independent assortment
a random process which introduces variation
chromosomes in males and females
F: XX
M: XY
what is a fertilised ovum
a zygote
Interphase: preparation for division
individual chromosomes unravelled to allow access to genetic material, enabling new proteins to be synthesised
Cell synthesises additional cytoplasmic proteins, organelles and copies of DNA for 2 new cells.
Vital that DNA identical in structure and quantity. Achieved by DNA replication.
4 stages of mitosis:
- prophase
- metaphase
- anaphase
- telophase
prophase: (5)
- chromosomes condense because microtubules in cytoplasm form 3D structure; the spindle.
- Chromosomes now thicker and shorter. Each chromosome visible as 2 stands; ‘chromatids’
- Centrioles move around nuclear envelope and position themselves at opposite sides of the cell. This forms the 2 poles of the spindle’
- Spindle fibres form between poles
- Breakdown of nuclear envelope, forming vesicles in the cytoplasm because pores in envelope not large enough for whole molecules of DNA to pass through.
2.
metaphase
centromeres attach to spindle fibres at the equator
what is the spindle involved in
organisation of cell fibres
what is the widest part of the spindle known as
the equator
what produces spindles
centrioles
anaphase
centromeres split and spindle fibres shorten, which pulls the 2 halves of each centromere in opposite directions.
One chromatid of each chromosome is pulled to each of the poles
ends when separated chromatids reach the poles and spindle breaks down
telophase
reverse of prophase
chromosomes unravel and nuclear envelope reforms so 2 sets of genetic info are enclose in separate nuclei
cytoplasmic division in animal and plant cells
ANIMAL
cell surface membrane constricts around centre of cell
Ring of protein filaments bound to inside of cell surface membrane contracts until cell is divided in 2 new cells (proteins actin and myosin).
PLANT
instead of constriction, they synthesise a cell plate between the 2 new cells and Golgi apparatus carries material for a new cell move along the microtubules and fuse.
Why is mitosis important
insures genetic consistency (identical): growth, repair, asexual reproduction
what type of cell doesn’t carry out mitosis or meiosis
prokaryotes e.g. bacteria. Do not contain chromosomes. Thus, binary fission: one cell splits into 2 identical cells
early embryo cells are known as…..
TOTIPOTENT (can develop into complete human)
when does a blastocyst form and what is it
a hollow ball of cells formed 5 days after conception
outer layer goes on to form placenta
inner cell mass forms tissues of developing embryo known as ‘pluripotent embryonic stem cells’
what are adult stem cells
multi potent
eg. red and white blood cells
in plants can cells de - differentiate
yes, and many remain totipotent
why can plants be reproduced in tissue culture
totipotency. Small pieces of plants (explants) are surface sterilised and placed on solid agar medium with nutrients and growth regulators.
Cells divide to form mass of undifferentiated cells known as a callus.
what are human stem cells used for
replacing regenerating engineering tissues organs cells
how are stem cells used in research
embryo allowed to grow to form blastocyst
cultured to see if stem cells grow
isolated from each embryo and rest of embryo discarded
stem cells cultured and used in research
2 ways around tissue rejections
tissue typing
drugs
method of therapeutic cloning
- Diploid cell removed
- nucleus removed
- fused with ovum that has haploid nucleus removed
- diploid cell
- somatic cell nuclear transfer
- cell stimulated to divide via mitosis
uses of adult stem cells
produce cells for transplantation
treat patients with burns
use own stem cells for transplantation, e.g. trachea from donor windpipe is stripped of cells and other patients is grown on surface. Costly, and isolation and culturing of stem cells is difficult.
using stem cells to treat burns
patients skin stem cells from unburned area cultured
cells multiply
form sheet of cells covering bottom of culture flask
transplanted to burn
however, cells cannot differentiate so do not contain structures such as sweat glands
why would we reprogramme somatic cells
to make induced pluripotent stem cells
how is reprogramming somatic cells beneficial
- overcome problem of cell rejection
- address ethical concerns with use of embryonic stem cells
- effective for range of diseases e.g. parkinsons
what are embryonic and pluripotent stem cells used for in research
human development and diseases
help understand how cancer cells develop
how certain birth defects occur
provide a source of normal human cells in virtually any tissue type for use in screening new drugs.
who regulates the laws on stem cell usage
parliament - HOC and HOL (+advisory committees).
acceptable usage of human embyos: (5)
promote advances in infertility treatment
increase knowledge on congenital disease
increase knowledge on miscarriage causes
develop more effective contraceptive methods
develop methods for detecting gene/ chromosome abnormalities in embryos prior to implantation
where is development controlled
nucleus
what is the role of the EPIGENOME
influences which genes can be transcribed in a particular cell.
DNA is wrapped around histone proteins and both the DNA and the histones have chemical markers attached to their surface. These chemical markers make up the epigenome
Helps control change from single celled zygote to fully formed adult. During development, epigenetic changes bring about cell specilisation
why (how) are cells specialised
only some genes switched on and produce active mRNA that is translated into proteins within the cell
what is histone modification
the binding of epigenetic markers to histone tails alters how tightly DNA winds around histone proteins
tightly: genes inactive ‘switched off’ as cannot be transcribed to mRNA
tissue definition
a group of specialised cells working together to carry out one function
organ def
a group of tissues working together to carry out one function.
eg. muscle, nerve and epithelium working together in heart
organ system def
a group of organs working together to carry out a particular function e.g. circulatory system
what results in changes in epigenome
signals from inside and outside the cell
Changes in the epigenome alters the genes transcribed at specific times and locations
DNA replication and the epigenome
copying of epigenome during DNA replication ensures changes during development are passed onto new cells
what are master genes
control the development of each segment (arms/legs)
Produce mRNA that is translated into signal proteins
what are signal proteins
‘switch on’ genes responsible for producing proteins needed for specialisation of cells in that segment
what are differences in phenotypes between members of a population caused by
genotype
environment in which individual develops
what characteristics does genotype control
blood group.
Characteristics show ‘discontinuous variation’; they have phenotypes that fall into discrete groups with no overlap
characteristics affected by environment and genotype
height
‘continuous variation’’
controlled by genes at many loci; known as ‘polygenic inheritance’.
controlled by environment: directly or by influencing gene expression
what is monohybrid inheritance and polygenic inheritance
MONO= each locus is responsible for a different heritable feature
POLY= more than one gene involved in inheritance of a characteristic
what are multifactorial conditions (diseases)
several genetic AND environmental factors involved in disease development
why has height been increasing over years
- taller men have more children s gradual change in populations genetic make up
- greater movements of people = less interbreeding
- better nutrition = greater child growth
- improved health + reduction of infectious diseases
- end of child labour = more energy into growth
- better housing heating + quality clothing = less energy to heat body
what is the dark pigment in hair and skin
melanin, made in melanocyte cells
how is melanin made and what happens when more UV light
- A stimulating hormone activated melanocyte cells
- Receptors for melanocyte stimulating hormone (MSH) receive MSH
- Melanocytes place melanin into organelles- ‘melanosomes’
- Melanosomes transferred to nearby hair and skin cells- where they collect around the nucleus to protect their DNA from UV light
- More receptors = darker skin and hair
UV light increases amount of MSH and MSH receptors - so melanocytes more active + darker skin
Hair lightens because UV light causes chemical and physical changes to melanin and other proteins in hair cells. Melanin destructed by UV light
what enzyme makes melanin
enzyme tyrosinase changes amino acid tyrosin into melanin
what environmental factors can trigger changes in epigenome and affect gene expression
medecines
drugs
diet
what causes a tumour
rate of cell multiplication is faster than cell death
cancer causes
- DNA damage
- Carcinogens
- Mutations when cells divide - DNA incorrectly copied in gamete formation ‘inherited cancer’
2 gene types which have a role in controlling cell cycle in play a part in triggering cancer
- oncogenes
2. tumour suppressor genes
what do oncogenes do
code for the proteins which stimulate transition from one stage in cell cycle to next
DNA mutations// epigenetic changes= cell cycle continually active, excessive cell devision + tumour
what do tumour suppressor genes do
produce proteins which stop the cell cycle.
DNA//Epigenetic changes= inactivated genes- so no brake on cell cycle
Chemical environment and cancer
smoking: carcinogens in tar
Tar lodges in bronchi and causes damage to surrounding epithelial cells
physical environment and cancer
UV light
cancer cells spread to other parts of body in blood and lymphatic system if tumour not removed
diet and cancer
fruit and veg= antioxidants destroy radicals
radicals = ageing + cancer through accumulated damage
can a virus infection trigger cancer
yes.
Virus RNA may contain an oncogene picked up from one of its hosts and transfer it onto the cell it infects
