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biology unit 2 - area of study 1

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what are chromosomes

-Structure containing single DNA molecule and associated proteins - they carry genes

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295 questions
What are chromosomes
-Structure containing single DNA molecule and associated proteins - they carry genes
What do chromosomes look like
Various shapes and sizes – appearance changes over life of organism - when condensed they are depicted as long oval shapes - when uncondensed they are just floating strings
What does each chromosome possess
Each chromosome has a set of genes – passed on to daughter cells in mitosis and germ cell in meiosis
What chromosomes do prokaryotes have
Prokaryotes have a single circular chromosome – may also contain small circular DNA called plasmids which can move between cells
What is histone proteins
Histone proteins are the substance that DNA is wrapped around
What is a nucleosome
They are sections of DNA which is wrapped around histone proteins nucleosomes are particles, so they give DNA the appearance of string beads
What is the main function of nucleosomes
Serve to package DNA efficiently and protect it from enzymatic degradation
What happens to nucleosomes when chromosomes are condensed
When chromosomes are condensed nucleosomes fold producing supercoils
What is a centromere
Chromosomes have a constriction point called a centromere which divides the chromosome in to two sections called chromosome arms
What are chromosome arms
They are the two sides of a chromosome separated by a centromere
What are the names for the two types of chromosome arms
The shorter arm is the p arm and the longer the q arm – p arm is always on top
What are the names for the four positions centromeres can be in
Metacentric, submetacentric, acrocentric and telocentric
Where is the centromere if a chromosome is metacentric
Centromere is in the centre - p and q are equal
Where is the centromere if a chromosome is submetacentric
Centromere closer to one side making q almost double the length of p
How many genes does each DNA molecule have
Each DNA molecule has many genes
What is a locus
Each gene has a particular position called a locus on a specific chromosome
What is spacer DNA and what does it do
- Genes of each DNA molecule are separated by regions called spacer DNA → spacer DNA doesn’t code for a protein product → they space genes far enough apart that it enables enzymes and other molecules to interact with genes easily
What is a ploidy level
The number of sets of chromosomes in a cell
What is gametes ploidy level and how many sets of chromosomes do they have
Gametes have one set of chromosomes and are haploid (n)
What are somatic cells ploidy level and how many sets of chromosomes do they have
Somatic cells are diploid (2n) – two sets of chromosomes (1 from each parent) -> Humans have a diploid number of 46
What are homologous chromosomes
Two chromosomes in a matching pair - have the same genes found in the same location -> same genes but different DNA (different variations of each gene - one maternal and one paternal)
What are sister chromatids
They are two chromosomes that are genetically identical and are created when DNA is duplicated
What are sex chromosomes
Chromosomes involved in the determination of a person’s sex
What are allosomes
Sex chromosomes
What is an autosome
Chromosomes not involved in sex determination
What are mating types
Some organisms (fungi and algae) don’t have allosomes and therefore don’t have sexes instead they have mating types
What are organisms called is they have two similar allosomes
Individuals with two similar allosomes are of the homogametic sex
What are organisms called is they have two different allosomes
Individuals with 2 different allosomes are of the heterogametic sex
What is haplodiploidy
In some species sex is determined by haplodiploidy – males develop from unfertilised eggs so are haploid and females are derived from fertilised eggs hence they are diploid (bees and wasps)
What are some environmental factors that can determine a species sex
Some species sex is determined by environmental factors such as temperature (turtles and crocodiles), day length (some types of shrimp) or richness and availability of food resources (types of worms) → when sea turtles lay their eggs if the temperature is between 32 and 34 degrees there will only be females but if the temp is between 26 and 18 degrees, they will all be male
What is chromosome banding
Chromosome banding refers to alternating light and dark regions along the length of a chromosome, produced after staining with a dye. A band is defined as the part of a chromosome that is clearly distinguishable from its adjacent segments by appearing darker or lighter
What are banding types used for
Banding types are specific and consistent in each species hence they can be used to distinguish between chromosomes and to identify changes in chromosome structure which may be associated with genetic abnormality
What is a karyotype
A karyotype is the image or picture of the full set of chromosomes from an organism’s cell – represented by chromosomes arranged in pairs according to length and centromere position
What are karyotypes used for
Karyotypes allow scientists to compare chromosomes of related species and allows them to identify changes associated with genetic abnormalities such as changes in chromosome number or structure
What is the human karyotype
The human karyotype is made up of 22 pairs of autosomes and 1 set of allosomes → the autosomes are numbered 1-22 and are order largest to smallest → allosomes are usually shown after autosomes
Give a brief description of a somatic cell
Somatic cells or body cells are diploid and undergo mitosis
Give a brief description of a gamete
Gametes or sex cells are haploid cells that are created when a diploid cell undergoes meiosis forming 4 haploid gametes
Do all somatic cells divide
No, some differentiate becoming specialised and lose their ability to divide
What are the four stages of mitosis
Prophase, metaphase, anaphase, and telophase – followed by cytokinesis
What occurs in the first stage of mitosis
The first stage is prophase → nuclear division begins (the nucleus begins to split in two) – nuclear membrane dissipates → chromosomes condense and become visible – appear as double stranded → the nucleolus shrinks (nucleolus produces and forms ribosomes – found in the nucleus) → centrioles move to opposite sides of the cell → spindle microtubules or fibres form between the two centrioles – spindle fibres are made of contractile proteins
What occurs in the second stage of mitosis
Metaphase is second and is the longest stage of mitosis (50% of the time) → chromosomes are fully condensed and are lined up along equator → each chromosome is attached to a spindle fibre and each chromatid is slowly being pulled to each pole with equal forces from each direction
What is the nucleolus
Nucleolus produces and forms ribosomes – found in the nucleus)
What are microtubules
They are contractile proteins
What is kinetochore
It is a protein that connect spindle fibres and chromosomes
What is the third stage of mitosis
Anaphase is the third and shortest phase only lasting a few minutes → centromere holding the two chromatid separates – each chromatid (now a single chromosome) begins moving to opposite poles by shortening microtubules (contractile proteins)
What occurs in the last stage of mitosis
Telophase is the last stage before cytokinesis → chromosomes arrive at the two poles and are grouped at each end of the cell → revert to extended fibres of chromatin and nuclear membrane forms around each group of chromosomes → spindle microtubules disassemble
What are the 2 main stages of the cell cycle
Interphase and M phase (mitosis and cytokinesis)
What are the stages of interphase
Interphase is broken in to three stages – gap 1 (G1), synthesis (S) and gap 2 (G2)
What happens in the first stage of interphase
G1 is the longest stage and takes around 8-10 hrs → in this stage the cell grows and makes proteins and organelles → if the cell is big enough at the end of the stage the cell will pass the restriction or check point and continue to the S phase
What is Gap 0 or G0
Some cells such as nerve cells and differentiated tissue cells never leave G1 and don’t undergo mitosis – this is known as G0 stage
What occurs in the second stage of interphase
S phase is the second one in interphase and takes 6-8 hours → DNA is replicated, and centrioles are duplicated → it ends when the DNA in the cell has doubles – each chromosome is now made from two sister chromatids → chromosomes become visible at the start of M phase (mitosis and cytokinesis) – evidence for S phase
What is the last stage of interphase
G2 is the phase when the cell actively prepares for mitosis and takes 4-6 hours → period of high metabolic activity and lots of protein production (for histones and spindle fibres) → after the phase ends the cell goes through a second checkpoint to ensure all genetic material is doubled and the cell is big enough to undergo division
Where are the two checkpoints in the cell cycle and what do they check for
1. after G1 - if the cell is big enough at the end of the stage the cell will pass the restriction or check point and continue to the S phase 2. after G2 - cell goes through a second checkpoint to ensure all genetic material is doubled and the cell is big enough to undergo division
What is cytokinesis
Division of cytoplasm and is the last stage before the cell becomes two and re-starts interphase
What is a cleavage furrow
A cleavage furrow appears at the equator of the cell before the cell splits in to two daughter cells
What can the daughter cells do after they are created
Daughter cells can either grow via cell enlargement, become specialised or continue to divide
What are some features dividing plant cells dont have but somatic cells do
Most dividing plant cells do not contain asters or centrioles
Where are new cells formed in the plant body
New cells are formed in specialised areas of the plant body called meristems – plants contain many meristems but there are four types
What are the four meristems of a plant
Apical meristem, young leaves, axillary meristems, and root meristems
Where are apical meristems
Growing tip or apex of the plant which divides causing the plant to grow
What are young leaves
They are a type of meristem and they demonstrate active growth
Where are axillary meristems
Buds of developing leaves or flowers form in the axils of plants (axils are the upward angle between the main stem and a leaf or branch)
What are root meristems
They are a place of active growth - growing tips of roots
Why cant cytokinesis occur in plants
Plant cells have a rigid cell wall so cytokinesis cannot constrict the cell membrane
What do plant cells do to divide instead of cytokinesis
Due to the rigid cell wall cytokinesis cannot constrict the cell membrane inwards so instead a new cell wall and membrane is grown along the cell plate (centre of the cell)
What is the importance of mitosis
Has two main purposes – growth and repair → also, important as it maintains the chromosome number of somatic cells -> Mitosis also is helpful as when a cell becomes too large and the surface area to volume ratio is too low so it has to divide which increase surface area to volume ratio and makes gas exchanged more efficient
Why is mitosis important for growth
→ multicellular organisms are grown from a single fertilised egg which divides increasing cell number → during period of growth cell replacement is higher than cell death however as you grow older and stop growing cell replacement occurs at the same stage as cell death
Why is mitosis important for repair
Responsible for the repair and replacement of damaged cells allowing your body to heal from injuries such as broken bones and scrapes → some organisms can generate new body parts when they are lost – sea star
What are two genes that help control the cell cycle
Proto-onco genes tumour suppressor genes
What is the function of protol-onco genes
Proto-oncogenes promote cancer, produce proteins that stimulate cell division, inhibit cell differentiation, and decreases apoptosis - -> also triggers apoptosis when cells are faulty, dividing too often, tumourous etc
What is the function of tumour suppressor genes
They slow down cell division, help repair damaged DNA, and inform cells when they need to activate apoptosis
What are tumour suppressor and proto-onco genes
They are two genes that control the cell cycle and they work together to control the cell cycle and when one is damaged or silenced problems tend to arise
What is apoptosis
Apoptosis or programmed cell death is the deliberate death of healthy cells → natural feature of healthy tissue and cells are preprogramed to die
What happens when cell reproduction and cell death is unbalanced
Cell reproduction and death is usually balanced – if there is too much reproduction it can lead to tumours and if there is too much it can lead to neurodegenerative diseases
What is the function of apoptosis
Apoptosis is a form of self-defence as well as it killed cells with viruses, old cells, cells with DNA damage, cells of the immune system, and cancerous cells
What are three reasons otherwise healthy cells die via apoptosis
→ not fully developed cells are killed – in the embryonic brain cells that are not incorporated into the brain network are killed via apoptosis → there are more than needed – it takes energy to keep extra cells alive so excess cells die via apoptosis → they have outlived their usefulness – foetuses have webbed toes and fingers and when this feature is no longer needed the cells connecting these extremities die via apoptosis – also when you recover from an illness any leftover immune cells that are not needed anymore die via apoptosis
What is syndactyly
Incomplete differentiation of toes or fingers is called syndactyly and is a result of a lack of apoptosis
What are the two signals to activate apoptosis
The mitochondrial pathway and the death receptor pathway
For what reason is the mitochondrial pathway activated
The mitochondrial pathway is a signal from inside the cell to activate apoptosis and begins when there is serious damage inside the cell (damaged DNA)
What are the four steps of cell death via the mitochondrial pathway
→ first proteins on the outside of the mitochondria are activated breaking down the mitochondrial membrane → this causes an enzyme known as caspase to enter the nucleus and destroy the DNA → organelles other than the nucleus and mitochondria are preserved as the cell is broken down into small fragments which are enclosed by a membrane → fragments bind to phagocytes which engulf them
What is the death receptor pathway
The death receptor pathway is a signal from outside the cell to activate apoptosis – cells have death receptors on their membrane that receive the message to begin apoptosis – process occurs in 5 steps
What are the five steps of the death receptor pathway
→ message is received, caspases are activated, contact to neighbouring cells is lost, and messages are sent to phagocytes → cells shrink and blebs (bumps) form of the outside of the cell → caspase enters the nucleus destroying all DNA → organelles other than the nucleus and mitochondria are preserved as the cell is broken down into small fragments which are enclosed by a membrane → fragments bind to phagocytes which engulf them
What are blebs
They are bumps on the outside of the cell which are caused by the onset of apoptosis via the death receptor pathway
What is caspase
Caspase is an enzyme that destroys DNA and it is used in apoptosis
What can too much apoptosis lead to
Too much apoptosis can lead to neurodegenerative diseases such as AD and PD
What can too little apoptosis lead to
Too little apoptosis can lead to the formation of cancer and can lead to autoimmune diseases
What is necrosis
Is a type of cell death that occurs when cells are damaged by chemical or mechanical trauma
What are the main two steps of necrosis
→ first the plasma membrane is damaged so it can’t control what enters and exits the cell, chromatin clumps, organelles swell, and the mitochondria has a loosely clumped texture almost resembling tufts of wool → cell swells and bursts, spreading intracellular contents over nearby cells causing inflammation
What causes necrosis
Chemical or mechanical trauma
What is chemotherapy
Chemicals that inhibit mitosis and causes apoptosis – also blocks growth promoting signals
What are some side effects of chemotherapy
Side effects – also effects cells that divide fast such as hair follicles and cells in the digestive tract
Define aneuploidy
It is when there is an abnormal number of chromosomes