3. Voice of the Genome Flashcards
Who is Robert Hooke?
He is the first person to view cells
Who were the two scientists to come up with cell theory?
Matthias Schleiden and Theodor Schwann
Three main ideas of “cell theory”
- All living organisms are made up of one or more cells
-Cells are basic functional unit in living organisms - New cells are produced from pre-existing cells
All living organisms share what common features?
- Cell surface membrane
- Cytoplasm
- DNA
- Ribosomes
What is meant by cell Ultrastructure?
Cell ultrastructure refers to the internal structure of the cell
What is a organelle?
A microscopic structure which does a particular job in a cell
Different structural elements and combinations of organelles in different cell types…
Prokaryotic cells- no internal membrane and smaller ribosomes
Eukaryotic cells - Several internal membrane-bound organelles and larger ribosomes
What is meant by the term specialised?
A specialised cell is a cell that has developed certain characteristics to perform specific function within an organism.
These adaptations enable the cell to carry out its particular role effectively
What is tissue?
A tissue is a group of cells that work together to perform a particular function
What is an organ?
An organ is a group of tissue working together to perform a particular function
What is an organ system?
Made from a group of organs with related function, working together to perform body functions within the organism
Example
- Circulatory system
- Digestive system
Limitations of a seeing cells under a microscope…
- The size of cells or structure of tissue may appear inconsistent in different specimen slides
- The treatment of specimens when preparing slides could alter the structure of cells
- Resolution may not be strong and therefore the some structures may not be seen
Why must cells be stained before placing them under a microscope?
Specimens may need to be stained as the cytoplasm and other cell structure may be transparent or difficult to distinguish
Common stains and there effects…
Methylene blue
- Stains animal cell nuclei blue
Iodine
- Stains starch-containing material in plant cells blue-black
Toluidine blue
- Stains tissue that contains DNA and RNA blue
What is the definition of magnification?
Magnification is how many times bigger the image of a specimen observed is in comparison to the actual, real-life size of the specimen
How can the magnification of a specimen be calculated
Total magnification = eyepiece lens magnification X objective lens magnification
Magnification = Image size / actual size
What is a graticule on a microscope?
A graticule is a small disc that has an engraved ruler
Different types of electron microscopes
Transmission electron microscope
Scanning electron microscope
What is the Cell Cycle
A series of stages that a cell undergoes, leading to its growth, replication and division to form two daughter cells
Three Phases of the cell cycle
- Interphase
- Nuclear division (mitosis)
- Cell division (cytokinesis)
Three phases of interphase
G1 Phase
S Phase
G2 Phase
Explain G1 Phase of Interphase
Cell growth: The cell grows in size and synthesizes various proteins an organelles
Function: The cell performs its normal functions, such as producing enzymes and other proteins necessary for its specific activities
Checkpoint: The cell checks for the DNA damage and ensures that the environment is favorable for DNA replication. If the conditions are not favorable, the cell ma enter a resting state called G0
Explain S Phase of Interphase
DNA Replication: The cells DNA replicated, resulting in two identical copies of each chromosome. This ensures that each daughter cell will have a complete set of genetic information
Chromosome Duplication: Each chromosome, originally consisting of one chromatid, is now made up of two sister chromatids held together by centromere
Explain G2 Phase of Interphase
Preparation for mitosis: The cell continues to grow and produce proteins
Final checks: The cell checks for any DNA damage that may have occurred during replication and ensures all DNA has been replicated correctly. It also verifies that the cell is ready to enter mitosis
Checkpoint: The G2 Checkpoint ensure =s the cell is ready for mitosis, confirming that DNA replication is complete and without errors
What happens in Cytokinesis?
Follows M Phase
One the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells
Animal cells
Cytokinesis involves constriction of the cytoplasm between the two nuclei
Plant cells
Cytokinesis involves a new cell wall forming
What happens in Prophase?
The chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA Molecule) that are joined together at the centromere
The two centrosomes (replicated in G2 phase just before prophase) move towards opposite poles (opposite ends of the nucleus)
What happens in Metaphase
Spindle fibres (proteins microtubules) reach the chromosomes and attach to the centromeres
Each sister chromatid is attached to a spindle fibre originating from opposite poles
What happens in Anaphase
The sister chromatids separate at the centromere (the centromere divides in two)
Spindle fibres (protein microtubules) begin to shorten
What happens in Telophase
Chromosomes arrive at opposite poles and begin to decondense
Nuclear nvelopes (nuclear membranes) begin to reform around each set of chromosomes
The spindle fibres break down
What does the root tip squash practical show?
- Growth in plants occurs in specific regions called meristem
- The root tip meristem can be used to study mitosis
-The root tip meristem can be found just behind the protective root cap
- In the root tip meristem, there is a zone of ell division that contains cells undergoing mitosis
Method - Root Tip Squash
- Garlic root is used ( the bulb can be encouraged to grow roots by suspending them over water for a week or two)
2) Prepare a boiling tube of 1m hydrochloric acid and place in a water bath at 60oc for 10 minutes
3) Remove the tip of the root ( about 1cm) and place in the warmed hydrochloric acid do 5 min
4) RInse the tips well in cold water using a pipette and blot dry with a paper towel
5) Cut approximately 2mm off the tip and place onto a microscope slide
6) Add a drop of a suitable stain (acetic orcein or tolodian blue)
7) The stained root tip is gently squared on a glass slide using a blunt instrument
8) View the side under the microscope
9) Cells undergoing mitosis can be seen and drawn
10) Annotations can then be added to these drawings to show the different stages of mitosis
What is a gamete
Gametes are the sec cells of an organism (egg and sperm cells)
How many chromosomes does a gamete have?
23 chromosomes (Haploid cell)
Adaptations of a sperm cell
Flagellum (tail) that allows them to swim towards the egg cell
Contains many mitochondria that provide energy for movement of the flagellum (swimming)
An acrosome that contains digestive enzymes to break down the protective glycoprotein layer ( a jelly-like coating known as the zona pellucida) surrounding the egg cell - Sperm cells ust penetrate this layer in order to fertilise the egg
Adaptations of a egg cell
Are much larger than sperm cells as most of their internal space contains food to nourish a growing embryo
Have a follicle cells that form a protective coating
Have a jelly like glycoprotein layer, known as the zona pellucida, that forms an impenetrable barrier after fertilisation by a sperm cell has occurred, to prevent other sperm nuclei from entering the egg
What is the process of fertilisation?
1) During sexual intercouse, semen is ejaculated high up into the vigina or fht efemale, near the cervix
2)The sperm cells then follow a chemical trail realesed by the egg cell and travel up the cervix to reach the uterus
3) The sperm cells thn travel into the oviduct containing the egg cell
4) If the sperm cell meets the egg cell in the oviduct fertilization occurs
5) ACROSOME REACTION - The head of the sperm releases digestive enzymes that make a path through the zone pellucida allowing the sperm to pass through the egg membrane
6) The egg cell them immediately releases vesicles known as cortical granules into the space between the egg cell membrane and the zona pellucida
7) CORTICAL REACTION - The chemical contained within the cortical granules causes the Zone pellucida to rapidly thicken and harden, preventing any more sperm cells from entering, ensuring only one sperm cell can fertilise the egg cell
8) The nucleus of the sperm cell then enters the egg and fuses with the nucleus of the egg cell
9) when the male and female gamete fuse it forms a zygote
10) the zygote goes through mitosis and new cells produced become specialized to perform particular functions
What is a gene
A length of DNA that codes for a single polypeptide or protein
What is a locus?
The position of a gene on a chromosome
Why are does a gene have the same locus on an other gene?
Each gene occupies a specific locus so that the gene for a particular characteristic i always found at the same position on a particular chromosome
What is an allele
Two or more different forms of a gene
What is autosomal linkage?
Autosomal linkage only occurs on the autosomes ( any chromosome that isn’t a sex chromosome)
Two or more genes on the same autosome do not assort independently during meiosis
instead these genes are linked and they stay together in the orgainal parental combination
These linked genes are passed onto offspring all together (through the gametes)
What is Sex Linkage?
Some genes are only present on one chromosome and not the other
As the inheritance of these genes is dependent on the sex of the individual they are know as sex-linked genes
- Most often the sex-linked genes are found on the longer X chromosome
Because males only have one X-Chromosome, they are much more likely to show sex-linkage recessive conditions
Females having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele
What happens in Meiosis I
The nucleus of the original parent cell is diploid (2n)
The homologous pairs (similar in shape, size and genetic content) of chromosomes are split up, to produce haploid nuclei
*same way as mitosis
What Happens in Meiosis II
Chromatids that make up each chromosomes separate to produce four haploid nuclei
(Both crossing over and independent assortment result in different combinations of alleles in gametes)
What is crossing over?
Crossing over is the process by which non-sister chromatids exchange alleles
can result in the new combination of alleles on the two chromosomes
Process of Crossing over
1) during meisosis 1 homologous chrmoskes pair up and are in very close proximity
2) The paired chromosomes are known as bivalents
3) The non-sister chromatids can cross over and get entangled
4) These crossing points are called chiasmata
5)The entangled places stress on the DNA molecules
6) As a result of this, a section of chromatids from one chromosome may break and rejoin with the chromatid from other chromosome
What is independent assortment?
Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignemtn of homologous pairs along the equator of te spindle during meisois.
Process of independent assortment
In meiosis I, homologous chromosome pair up and are pulled towards the equator of the spindle
- Each pair can be arranged with either chomosome on top, this is completely random
- The orientation of the homologous pair is independent/unaffected by the orientation of any other pair
The homologous chomosomes are then sperarated and pulled apart to diffrent poles
The combination of alleles that end up in each daughter cell depend on how the pairs of homologous chromosomes were lined up
What is a stem cell?
A stem cell is a cell that can divde (by mitosis) an ulimited number of times
Each new cell (produced when a stem cell divides) has the potential to remain a stem cell or the develop into a specilised cell
What is potency
The ability of stem cells to differentiate into more specialised cell types
What are the two main types of potency?
Totipotency
Pluripotency
What is totipotency?
Differentiate into any cell type found in an embryo,
Placenta, umbilical cord and Zygote
What is pluripotency?
Embryonic stem cells that can differentiate into any cell type found in an embro bit are not able to differntiate into cells forming the placenta and umbilical cord
What are multipotent cells?
adult stem cells that have lost some of the potency associated with embryonic stem cells and are no longer pluripotent
Benefits of stem cells
great potential to treat a wide-varity of diseases from diabetes and paralysis
Organ development from patients own stem cells reduces the risk of organ rejection and the need to wait for an organ donation
Adult stem cells are already used successfully in a variety of treatment acting as proof of benefits
Risk/issues of using stem cells
Stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient
There is a risk of cultured stem cells accumulating mutations that can lead to them developing into cancer
low number of stem cell donors
Social issues of stem cells
Embryonic stem cells can be collected before birth (from amniotic fluid) or after birth (umbilical cord) ad stored by a clinic - but this can be expensive and isn’t an option for everyone
A lack of peer reviewed clinical evidence of the success of stem cell treatment
educating the public sufficiently about stem cells can and cannot be used for
Ethical issues with stem cells
Stem cells may be sourced from unused embryos produced in IVF treatment - is it right ti use them? Who gives permission
Is it right to create embryos through therapeutic cloning and then destroy them? Who owns the embryo?
Should an embryo be treated as a person with human rights? or as a commodity?
What is meant by ‘switched on”
When stem cells differentiate certain genes and are expressed
How are stem celled differentiated
Under certain conditions, some genes in a stem cell are activated, whilst others are inactivated
mRNA is transcribed from active genes only
The mRNA is then translated to form protiens
These protiens are responsible for midofying the cell
As these protiens continue to modify the cell, the cell becomes increasingly specialise
The process of specialisation is irreversible
What is the definition of a transcription factor?
A transcription factor is a protein that binds to specific DNA sequencs to regulate the transcription of gentic information from DNA to messenger RNA
How do transcription factors increase increase the rate of transcription? ACTIVATORS
Activators work by helping tRNA polymerase to bind to the DNA at the start of a gene and to begin transcription of that gene
How do transcription factors decrease increase the rate of transcription? REPRESSORS
Repressors work by stopping RNA polymerase from binding to the DNA at the start of a gene, inhibiting transcription of that gene
What is a operon
Control the gene expression in prokaryotes
What is the function of a lac Operon
control the production of the enzyme lactase
Structure of the lac operon
- Promoter for structural genes
- Operator
- Structural gene lacZ that codes for lactase
- Structural gene lacY that codes for ermease (allows lactose into the cell
- Structura gene lacA that codes for transacetylase
What is epigenetics?
Epigenetics is the control of gene expression by factors other than an individual’s DNA sequence
it involves the switching - on and switching - off of genes, but without changing the actual genetic code
how can chromatin be chemically modified?
Methylation of DNA
Histone modification via acetylation of amino acid tail
what is an epigenome
A set of chemical modification to the DNA and histone proteins of an organism that regulate gene activity without changing the DNA sequence
Enviromental factors that can effect the epigenome…
Smoking, stress, exicite and diet
Internal signalling from the body’s own cells can also cause modification to occur
What happens to the DNA if it is wound around the histones more tightly?
DNA= switch off
gene and promoter region are more hidden from transcription factors and RNA polymerase
what does DNA methylation cause?
inactivation of genes
DNA methylation involves the direct additoon of methyl grop to cytosine bases wihc can influence gene expression
it supresses the trancription of the affected gene by inhibating the binding of transcription factors and enzymes needed for transcription
what does acetylation of histones do?
Acetyle groups can be added to lysine amino acides on histone protiens
lysine has a positivly chared R group, this forms ionic bonds with the neagativly charged phosphate backbone of DNA
- this helps DNA to coil tightly around the histone protien core
Adding acetyle gorups to lysine resides removes the positove ion and therefore removes a bond between the histone protien and the DNA, causing the DNA to not be wound round th histones as tightly
- RNA polymerase and transcription factors can bind more easily ans therefor gene expression can occue
