Topic 3 - Voice of the genome Flashcards
Describe the transport of a protein through a cell
- mRNA is transcribed off DNA and leaves the nucleus
- Protein enters RER and assumes 3D shape as it moves through
- Vesicles are pinched off the RER contain protein, they fuse to form flattened sacs of the Golgi apparatus
- proteins are modified within the Golgi, vesicles are pinched off containing the modified protein
- Vesicle fuses with the cell surface membrane releasing its contents (exocytosis)
Sperm cell
Sperm cell is motile, it has a flagellum enabling it to swim to egg.
Sperm body contains multiple mitochondria which provide energy through respiration to power the flagellum.
Egg cell (ovum)
Large cell incapable of independent movement.
Moved along oviduct from ovary to uterus by ciliated cells and muscle contractions.
Contains lipid drops and proteins to sustain egg till it fuses to uterus wall.
Acrosome reaction
- Acrosome in the head of the sperm nucleus fuses with the sperm cell surface membrane
- Contains digestive enzymes to digest the zona pellucida
Cortical reaction
- Once sperm penetrates membrane surrounding egg chemicals are released causing the zona pellucida to harden - preventing further sperm entering
- Sperm nucleus enters egg and fuses with ovum nucleus forming a zygote
Human chromosomes and gametes
Humans have 46 chromosome:
- 22 homologous pairs
- 1 sex chromosome pair ( XX or XY)
Gametes contain one chromosome from each homologous pair, so when they fuse the zygote has the full 46 chromosomes
Where + why
does meiosis occur
- Occurs in testes/ovaries of animals
- Helps maintain diploid nature of cells after fertilisation
- Allows genetic variation to occur among offspring
Independent assoirtment
only one chromosome from each pair ends up in a gamete
either chromosome from each pair can end up in any gamete
when joined with other gamete at fertilisation, the individual is guaranteed to be genetically diversity
crossing-over
during first meiotic division homologous chromosomes come together as pairs, all 4 chromatids are in contact
at contact point, chromatids break and rejoin - exchanging DNA between non-sister chromatids
several chiasmas (point at which chromatids break) can occur on the length of each pair of chromosomes - giving rise to a large amount of variation
Linkage
Any two genes with a locus on the same chromosome are linked together and tend to be passed on as a pair to the same gamete.
Strongly linked genes (close together on same chromosome) makes crossing-over unlikely, they will be inherited as a pair.
sex linkage
all the genes on the sex chromosomes are passed on with those that determine sex, they are sex-linked genes.
Male infertility
Chemical oscillin is required in sperm cytoplasm for fertilisation to occur.
Controls movement of calcium ions into/out of ovum cytoplasm stores
Low levels of oscillin may be linked to male infertility
Interphase
time of intense + organised activity where the cell synthesises new cell components eg organelles, membranes and DNA
G1 phase
period between the end of mitosis and start of S phase, period of growth and protein synthesis
S phase
period between G1 and G2 phase, DNA synthesis occurs during this period.
G2 phase
end of S phase and start of mitosis, period of growth and protein synthesis
Chromatin
substance within chromosomes consisting of DNA and protein
Prophase
chromosomes condense becoming thicker + shorter, with each chromosome visible as two chromatids
spindle fibres form, nuclear envelope breaks down forming vesicles in cytoplasm
metaphase
chromosomes move to centre of cell, centromeres attach to spindle
anaphase
spindle fibres shorten, pulling chromatids towards polls of the cell
telophase
opposite to prophase, chromosomes unravel and nuclear envelope forms
Cytoplasmic division
final reorganisation into two new cells, filaments and microtubules are involved. In plant cell synthesis a plate forms between two new cells.
importance of mitosis
Ensures genetic diversity, daughter cells are identical to each other and parent cell
essential for growth and repair
essential for asexual reproduction
growth and repair
all cells in the organism have the same genetic material
organism can regenerate and repair damaged parts of their body
asexual reproduction
many organisms reproduce without gametes.
They grow copies of themselves by mitosis producing offspring genetically identical to each other + parent
cells in the early embryo
After human zygote has undergone 3 complete cell cycles it consists of 8 totipotent cells that can develop into a complete human being
Plant tissue culture
Small pieces of plants (explants) are steralised and put on solid agar medium with nutrients + growth regulators
Cells divide and form callus (mass of undifferentiated cells)
Altering growth regulators in medium enables callus to differentiate forming groups of cells similar to plant embryo
Embryo develops into plant genetically identical to original plant
totipotent cells
undifferentiated stem cells which have the ability to differentiate and give rise to all specialised cells. They can give rise to more totipotent cells and to a whole human being
pluripotent cells
undifferentiated cells that also have the ability to differentiate, but as they are inactive they cannot differentiate into all cell types like totipotent stem cells.
multipotent cells
Can develop into more than one cell type, but are more limited than pluripotent
unipotent cells
can only mature into one type of cell
Therapeutic cloning
Diploid cell is removed from patient
Its cell or nucleus is fused with ovum without its haploid nucleus – diploid cell similar to zygote is formed
Cells could be stimulated to divide by mitosis
After 5 days blastocyst forms stem cells which are then isolated, and can be developed into tissue
This produces cell lines, which are genetically identical to patient from which diploid cell was taken
adult stem cell use
- Used in bone marrow transplants
- Treat burn patients
- Blood vessel production
Takahashi and Yamanaka 2006
reported successful reprograming of somatic mouse cells to make them pluripotent
They are known as induced pluripotent stem cells.
Human IPSC have since been produced resembling human embryonic stem cells
under what circumstances in embryonic cell research legally allowed
Promote advances in treatments for infertility
Increase knowledge about causes for miscarriage
Develop more effective methods for contraception
what controls development of a cell
nucleus and chemical messengers travelling through cytoplasm
dolly the sheep’s cloning process
They transported a nucleus from a mammary gland cell of one sheep into another sheep’s enucleated egg cell
The cell was then stimulated by electric shocks so it divides by mitosis
The diploid cell that formed the embryo was implanted into another adult sheep
The surrogate mother gave birth to a lamb who was chromosomally identical to mammary cell donor
what did dolly prove
The successful birth of Dolly suggests the cell must have contained all the info for making a complete organism
problems with cloning
Process not safe to try on humans
Animals cloned have health problems
Dolly got arthritis at a young age
Many factors could lead to low success rate
David and Sargent and gene expression
They extracted mRNA from undifferentiated and differentiated frog cells
Complimentary DNA strands were produced for all mRNA in differentiated (gastrula) cells using reverse transcriptase
These cDNA strands were mixed with (blastula) mRNA from undifferentiated cell
Complimentary strands of cDNA mRNA combined to produce double strand hybrids
When these hybrid strands were separated out, there remained a range of cDNA strands that had not been hybridised
The cells were expressing some of the same genes but also some different ones.
what is the epigenome
Epigenome influences what genes can be transcribed in a cell. DNA is wrapped around histone proteins, both DNA and histones have chemical markers attached to their surface. These chemical markers make up the epigenome
what happens when DNA is wrapped tightly around histone
genes are inactive, they can’t be transcribed. Gene therefor cannot make protein = it is switched off.
eukaryotes gene expression
Genes in uncoiled, accessible regions of the eukaryotic DNA can be transcribed into mRNA.
Enzyme RNA polymerase binds to section of DNA adjacent to gene to be transcribed (promoter region).
when is transcription prevented in eukaryotes
Transcription of gene can be prevented by protein repressor molecules attaching to the DNA of the promoter region – blocking attachment region.
Also, repressor protein can attach to regulator protein preventing it from attachment.
In both cases the gene is switched off and cannot be transcribed within cell.
what caused FOP
Inherited condition caused by gene mutation:
Bone cells are normally produced in growing limbs and in process where skeleton develops.
Here genes are expressed that produce all proteins needed to become specialised bone cells.
How are cells organised into tissue
Cells have specific recognition proteins (adhesion molecules) on their cell surface membrane.
Adhesion molecules helps cells recognise others like themselves + stick to them.
Small part of recognition protein is embedded in cell surface membrane, longer part extends from the membrane.
The extended part binds to complimentary proteins on adjacent cells.
cell
In multicellular organisms, cells are specialised for particular functions
tissue
group of cells working together to carry out one function
organ
group of tissues working together to carry out one function
organ system
group of organs working together to carry out a function
Gene expression and develop
Sequence of transcription and translation of genes determines sequence of changes during development.
Epigenome helps control changes from single-celled zygote to fully formed adult.
During development epigenetic changes bring about specialisation of cells.
Signals from inside and outside the cell result in changes to the epigenome that affect genes transcribed.
Copying of epigenome during DNA replication ensures that changes occurring during development are passed on to new cells.
Name 4 organ types in hermaphrodite flowers
petals
sepals
male stamens
female carpels
discontinuous variation
Not affected by the environment, controlled by genes at a single locus.
continuous variation
characteristics affected by both genotype and the environment
monohybrid inheritance
each locus is responsible for a different heritance feature, eg one gene codes for eye colour and another codes for height
polygenic inheritance
many genes involved in the expression of a characteristic
multifactorial inheritance
conditions where several genetic factors and one or more environmental factors are involved
Melanin production
Melanin is made in melanocytes (special cells) found in skin + hair follicles.
These are activated by melanin stimulating hormone (MSH). There are receptors for MSH on melanocyte cells.
Melanocytes place melanin into organelles called melanosomes.
Melanosomes are transferred to nearby skin + hair cells where they collect around the nucleus, protecting DNA from harmful UV.
More receptors -> darker hair + skin -> more protection from sunburn.
behaviour and the epigenome, rat experiment
Epigenetic difference between rats as pups grew up to be like their mother.
Offspring of good mothers (licked + groomed a lot) and bad mothers (rarely groomed + licked) were swapped.
Found two sets up pups were epigenetically different.
GR gene in pups with bad parent switched off due to methylation of gene.
Gene produces receptor protein that binds to stress hormone causing calm signals to be sent.
Low levels of GR protein = hormone level remains higher in blood and pup feels more stress.
Define cancer
when rate of cell division exceeds rate of cell death
Oncogenes (cancer triggers)
Code for proteins that stimulate transition from one stage to another in cell cycle.
DNA mutations or epigenetic changes in these genes can lead to cell cycle being continually active -> excessive cell division = tumour.
tumour suppressor gene (cancer triggers)
Produces suppressor proteins that stop the cycle.
DNA mutations or epigenetic changes in these genes eg more methylation inactivity means there’s no brake in the cycle.
Smoking - chemical risk factor for cancer
Greatest chemical risk is smoking which increases risk of lung cancer.
Tar lodges in bronchi and damages DNA surrounding epithelial cells.
UV light - physical risk factor for cancer
UV light physically damages DNA in skin cells.
Mole affected by UV can develop into tumour, if not removed can spread around the body.
Radicals and cancer
Radicals come from diet, the environment and can be produced by DNA’s own metabolism.
Radicals contribute to aging and cancer due to damage to DNA.
