Topic 3: Voice of the Genome COPY

Question 1

Describe and explain features that ALL prokaryotic cells have

Answer 1

Circular DNA= cell’s genetic material
70S ribosomes= made of RNA and protein, the site of ps
Cell membrane controls what enters and leaves
Cell wall= made of peptidoglycan

Question 2

Describe and explain features only some prokaryotic cells have

Answer 2

Flagella enabling the cell to swim
Slime capsule= slimy surface layer to protect and prevent dehydration
Pili= thin protein tubes allow bacteria to adhere to surfaces. Involved in conjugation

Question 3

Describe the structure and function of the centrioles

Answer 3

Centrioles are hollow cylinders made up of a ring of 9 protein microtubules.
These microtubules are arranged in a helix.
They from the spindle during mitosis and are involved in transport w/in the cytoplasm

Question 4

Describe the structure and function of the Golgi apparatus

Answer 4

Vesicles from the ER fuse to form flattened, membrane bound sacs.
The GA modifies and packages proteins in vesicles for transport
Hay transport vesicles, which move within the cell, and secretory vesicles which move molecules out of the cell, (exocytosis).

An example of a vesicle that stays in the cell is lysosome, spherical sacs w digestive enzymes. They’re bound by a single membrane.
Lysosomes break down unwanted structures or old cells that need to be replaced.

Question 5

Describe exocytosis of proteins

Answer 5

Transcription forms mRNA, which leaves the nucleus and joins onto a ribosome on the rough ER.
Protein moves through the ER assuming its 3-D shape en route.
Vesicles containing the protein are pinched off the rER.
These pinched off vesicles fuse to form flattened sacs of the Golgi apparatus. Proteins are modified within the Golgi apparatus.
Vesicles containing the MODIFIED protein are pinched off the G. ap.
Vesicle fuses with the cell membrane and releases the protein.

Question 6

State the function of mitosis and meiosis. Where do they take place?

Answer 6

Mitosis produces identical cells for growth, repair and asexual reproduction.
Meiosis forms gametes w variation, it takes place in the ovaries and testes.
Interphase occurs before mitosis and meiosis

Question 7

Is how is variation achieved in meiosis?

Answer 7

During meiosis only one chromosome from each pair ends up in each gamete to produce variation.
The mixing up is completely random, so a large number of possibilities exist.
This is known as independent assortment
Crossing over produces chromosomes with new allele combinations from both parents, leading to variation. There is no crossing over between the sex chromosomes.

Question 8

Describe and explain meiosis I

Answer 8

Before meiosis, interphase occurs- which is cell growth and DNA replication.
Chromosomes condense and line up in homologous pairs in the cell centre. Crossing over occurs: this is when all 4 chromatids come into contact.
At these contact points (chiasmata) chromatids break and rejoin, exchanging DNA sections between non-sister chromatids. This produces recombinant chromosomes which leads to variation.
Anaphase I- Chromosomes are pulled away from each other by spindle fibres
Telophase I- nuclei reforms. 2 new cells are formed w 23 chromosomes (46 chromatids)

Question 9

Explain the concept of linkage

Answer 9

Some characteristics are inherited together.
Linkage is when 2 genes w/ a Locus on the same chromosome will be passed on together to the same gamete.
This is because crossing over is very unlikely to happen.
Genes on a single chromosome make up a linkage group

Question 10

Why do some diseases such as colourblindness disproportionately affect men?

Answer 10

As men only have one X chromosome they often have one allele for sex linked genes, even if it is recessive. Therefore men are more likely to inherit a recessive genotype that leads to a genetic disease like colourblindness.

Question 11

Describe the cell cycle

Answer 11

The cell cycle is split into 2 phases: interphase and division.
Interphase is split into G1, S and G2
G1: Protein synthesis occurs. Production of new organelles, rapid growth.
S: DNA replication, chromosomes are copied.
G2: Cell growth, some organelles divide. Hay a buildup of energy reserves.
Respiration occurs in G2 and G1
G0: Cells that wont divide again enter this stage

Question 12

Describe prophase

Answer 12

Chromosomes condense, getting shorter and fatter. Each chromosome is seen as two identical strands called sister chromatids, produced by replication, joined at the centromere.
Microtubules from the cytoplasm form a 3-D spindle.
Centrioles move to opposite sides of the cell to form the two spindle poles. The widest part of the spindle is the equator.
The nuclear envelope breaks down

Question 13

Describe metaphase

Answer 13

Chromosomes line up in the middle of the cell

Chromosomes’ centromeres attach to spindle fibres at the equator.

Question 14

Describe late anaphase

Answer 14

Spindle fibres shorten and pull 2 halves of each centromere to opposite poles. The centromeres split.
When the chromatids reach the poles the spindle breaks down.

Question 15

Describe telophase

Answer 15

Chromosomes unravel. The nuclear envelope reforms so that two sets of genetic information are enclosed into separate nuclei

Question 16

Describe cytoplasmic division

Answer 16

In animal cells, the cell membrane constricts around the cell centre. A ring of actin or myosin contract until the cell is divided

Plant cells synthesise a new cell plate between two new cells. Golgi Vesicles carrying material for a new cell wall move along microtubules and fuse.

Question 17

How is DNA organised in chromosomes?

Answer 17

DNA is a double helix.
DNA winds around histone proteins.
DNA and histone proteins coil to form chromatin fibre. Chromatin fibre attaches to a protein scaffold, forming loops.
Folding the protein scaffolding produces the condensed chromosome structure

Question 18

Describe binary fission.

Answer 18

Prokaryotes don’t have chromosomes so they can’t do mitosis or meiosis. instead, they asexually reproduce via binary fission.
This is the simplest form of reproduction, where one cell splits into 2 identical cells.
Some bacteria multiply in this way every 20 mins

Question 19

what is a stem cell?

Answer 19

Undifferentiated cells. Embryonic stem cells are totipotent, meaning they have the potential to develop into any total individual.
Stem cell research is controversial because they need to be obtained from human embryos.

Question 20

How do embryonic stem cells form?

Answer 20

5 days after fertilisation, a hollow ball of cells called a blastocyst is formed.
There, the outer cells form the placenta and inner cells form the embryo. These cells are called pluripotent scs because they can form most cell types.

Question 21

What happens to embryonic stem cells as they develop?

Answer 21

As the embryo develops, pluripotency decreases because cells gets more specialised. By 3 months, cells are fully differentiated

Question 22

Describe adult stem cells

Answer 22

Even in adults some cells have capacity to differentiate into a variety of different cell types. These are multipotent stem cells.

Question 23

Describe the structure and function of ribosomes and mitochondria

Answer 23

Ribosomes are small organelles made of RNA and protein attached to the ER or free in the cytoplasm. Involved in ps.
In mitochondria the inner membrane folds to form finger like projections called cristae. It’s the site of aerobic respiration

Question 24

Explain the structure and function of the rough and smooth ER

Answer 24

The rER consists of many interconnected, membrane bound flattened sacs.
Ribosomes are attached on the outer surface
Proteins made on these ribosomes are transported through the ER to other parts of the cell.

The smooth ER makes lipids and steroids. It has the above structure, but no attached ribosomes

Question 25

Where are pluripotent stem cells obtained?

Answer 25

Pluripotent sc for research can be isolated from spare embryos from IVF treatments.
The embryos are left to grow to form blastocysts.
The embryos are cultured for a further period of time to see if stem cells are formed.
The stem cells are isolated from each embryo and the rest of the embryo is discarded.

Question 26

What is therapeutic cloning?

Answer 26

A diploid cell is taken from a patient, the nucleus is removed and placed in an enucleated ovum.
The process is somatic cell nuclear transfer.
The cell is stimulated to divide by mitosis into a blastocyst to form pluripotent scs. These can develop into genetically identical tissues to the patient.
Therapeutic cloning was allowed by HFEA in 2004, but cloned embryos must be destroyed after 14 days and cannot be for reproductive purposes

Question 27

Describe laws surrounding stem cell use

Answer 27

Adult use is advocated.
The HFEA regulates research on human embryos. Until 2001 embryos were only allowed to be used in the treatment of infertility, to understand miscarriage, contraception, to know about the causes of congenital disease and for PGD.
After 2001 the law was further extended to allow research into spare embryos from IVF and to use animal-human embryos

Question 28

Give advantages and disadvantages of Adult scs in transplantation

Answer 28

Adult scs move into the patients bone marrow and produce healthy blood cells
Scs are injected into brains/joints to replace damaged neurones or treat damaged cartilage in arthritis patients.
Used to treat skin burn victims, but new skin won’t have any sweat glands etc
Tissues developed by scs can cause rejection for the patient so to avoid this, drugs or tissue typing is used.
Culturing and isolating scs are difficult and expensive

Question 29

What are IPSCs

Answer 29

Somatic cells can be reprogrammed to make them pluripotent. These cells are called Induced pluripotent scs (IPCs.)
They’re effective in treating haemophilia, Parkinson’s etc.
For research, IPCs help understand how cancer cells develop, how birth defects occur.
They provide normal human cells of any tissue type which can be used to screen new drugs.
Therefore IPSCs would overcome the problems of rejection and address ethical concerns with the use of embryonic stem cells

Question 30

How do cells get specialised

Answer 30

As cells divide after fertilisation they become specialised bc only some genes are switched on and produce active mRNA that becomes translated.

Question 31

Who showed that different genes are expressed in different cells?

Answer 31

Dawid and Sargent extracted mRNA from diff and undiff cells.
Using reverse transcriptase, complimentary DNA strands were produced for mRNA in DIFFerentiated cells.
These cDNA strands from differentiated cells were mixed w the mRNA from the undiff cell to form double-stranded hybrids.
When these hybrids were separated out, there remained a cDNA strand that had not been hybridised: the two cells were expressing some of the same and some different genes

Question 32

What is the difference between the genome and the epigenome?

Answer 32

The genome is all the DNA containing a full set of genes.
The epigenome consists of all the chemical tags attached to the DNA and the histones. The epigenome influences which genes can be transcribed.

Question 33

How can epigenetic changes prevent transcription?

Answer 33

Epigenetic markers like methyl and acetyl groups modify the histone, affecting how tightly the DNA is wrapped around the histone. When the wound tightly, RNA polymerase can’t bind, the gene cannot make the protein so it is switched off.
Methylation of DNA may also attract proteins called protein repressor molecules. These attach to the promoter region and prevent RNA polymerase binding.
OR protein repressor molecules bind to the regulator protein. All stop transcription, so the gene is switched off.

Question 34

Describe and explain the lac operon model

Answer 34

E coli metabolise glucose to respire. But, if glucose isn’t present in the environment, they can use lactose. Beta- galactosidase hydrolyses lactose into glucose and galactose. Genes that code for proteins involved in lactose metabolism are called the lac operon.

If NO HAY lactose, a repressor protein binds to the operator region which is next to the promoter region. This prevents RNA polymerase from binding so prevents transcription of beta-galactosidase.

If lactose is present, it binds to the repressor protein, changing its shape and preventing it from attaching to the operator. RNA polymerase binds to the promoter and the beta-galactosidase gene IS expressed, allowing it to be transcribed and translated.

Question 35

What must happen in order for transcription to occur?

Answer 35

RNA polymerase must successfully bind to the promoter region.
This is a non coding region next to the gene being transcribed.
The attachment of a regulator protein is also required to start transcription.
Otherwise genes remain switched off

Question 36

Describe FOP

Answer 36

FOP is an inherited gene mutation causing bone growth in places like muscle.
In FOP, a gene coding for proteins for specialised bone cell is not switched off in WBCs.
When tissue gets damaged, WBCs produce this protein which diffuses into surrounding muscle cells, leading to bone growth.

Question 37

How are cells organised?

Answer 37

Specialised cells group into clusters to work together as tissue. Cells have adhesion molecules, or specific recognition proteins that help similar cells recognise each other and stick together.
A small part of each recognition protein is embedded into the cell membrane, and a larger part extends from the membrane.
This extended section binds to complimentary proteins on adjacent cells.
So, if cells from different tissues are separated and then mixed together, they reform into their original tissues as the adhesion molecules and recognition proteins bind.

Question 38

How is tissue organised and reorganised as the embryo develops?

Answer 38

In the embryo, cells form tissues as they start their specialised functions.
Genes coding for recognition proteins are switched on.
During development, cells change the type of recognition proteins they produce, leading to reorganisation of tissues.

Question 39

What is discontinuous variation?

Answer 39

In discontinuous variation, environment has no effect on the phenotype eg blood type.
The characteristics are controlled by genes at a single locus.
The phenotypes fall into discrete groups with no overlap.

Question 40

What is continuous variation?

Answer 40

Characteristics affected by both genotype + environment eg height show cont variation.
The characteristics are controlled by genes at many loci = polygenetic inheritance.
The environment can also cause epigenetic changes to gene expression, causing more variation.

Question 41

What is the difference between polygenetic and monohybrid inheritance?

Answer 41

Monohybrid inheritance is when characteristics are produced by allele interaction at a single locus. Each locus is responsible for a different trait.
Polygenetic inheritance is when characteristics are produced by allele interaction at many loci

Question 42

How can certain diseases be multifactorial?

Answer 42

Several genes may create susceptibility to a disease, but environmental factors trigger them. Conditions where several genetic factors and >1 environmental factors are involved are multifactorial

Question 43

Describe and explain melanin

Answer 43

Melanin is activated by an MSH hormone and is made in melanocyte cells in the skin + hair.
Melanocytes place melanin into organelles called melanosomes. These transfer onto hair and skin cells where they collect around the nucleus, protecting DNA from harmful UV light.
UB increases the amount of MSH + MSH receptors, making melanocytes more active, darkening skin. Hair lightens due to destruction of melanin by UV light.

Question 44

What is the difference between a regulatory gene and a structural gene?

Answer 44

Regulatory genes make repressor proteins that switch other genes off. Structural genes make proteins

Question 45

Explain why a fat yellow mouse and a small brown mouse are genetically identical despite appearing different.

Answer 45

In the fat yellow mouse, the Agouti gene is NOT methylated, so it is expressed. The Agouti protein binds to MSH receptors and prevents melanin production.
The mouse has similar receptors in the brain. The Agouti blocks the receptors, causing overeating.
In the small brown mouse, the Agouti gene is methylated so it is NOT expressed.
However if a pregnant fat yellow mouth is fed a methyl rich diet, her young will be slim and brown because the Agouti gene will be methylated.

Question 46

How can behaviour cause epigenetic changes?

Answer 46

There was an experiment where good affectionate mothers and bad mothers swapped offspring. In a good mother with bad offspring, high licking and grooming leads to no methylation of the GR gene in offspring so it is expressed. The GR gene produces a receptor that binds to the stress hormone glucocorticoid. This causes low anxiety and high licking and grooming.
In the bad mother, low licking and grooming leads to methylation of the GR gene, so it is NOT expressed and is switched off. Glucocorticoid levels remain high, increasing anxiety and leading to low levels of licking and grooming. The two types of pups are epigenetically different. .

Question 47

Describe cancer

Answer 47

Cancer occurs when the rate of cell division is greater than cell death. This causes tumour growth often in tissues with high rate of mitosis like lung or bone marrow.
DNA damage, mutations or epigenetic changes to DNA cause cancer because they result in uncontrolled cell division.
DNA damage arises from physical factors (UV light, asbestos) and chemical factors (carcinogens).
If DNA is incorrectly copied in gamete formation, cancer can be inherited.

Question 48

How can epigenetic changes cause cancer?

Answer 48

epigenetic changes to DNA can activate oncogenes and inactivate tumour suppressor genes which lead to cancer.
Activation of oncogenes means overproduction of proteins for cell growth and activity, making them cancerous.
Inactivation of tumour suppressor genes means p53 isn’t made. Therefore it cannot stop faulty cells going through the cell cycle and cancerous cells can continue dividing.

Question 49

How is the cell cycle controlled?

Answer 49

During each stage of the cell cycle, proteins are produced.

These proteins either stimulate or stop the next stage of the cycle by activating or inhibiting enzymes.

Question 50

What gene types control the cell cycle?

Answer 50

Oncogenes and tumour suppressor genes control the cell cycle.
Oncogenes code for proteins that stimulate cell growth and activity.
Tumour suppressor genes code for suppressor proteins that stop the cell cycle.
p53 is a tumour suppressor protein. p53 inhibits enzymes at the G to S transition, preventing a faulty cell copying DNA.
The faulty cell thus cannot process in the cell cycle

Question 51

What happens in order for Cancer to occur? Why do older people get it more?

Answer 51

In order to cancer to occur, there must be damage to >1 parts of the cell control system.
Older people are more likely to get it because they’ve accumulated more mutations.

Question 52

How can cancer be inherited?

Answer 52

Mutations in the BRCA1 gene predisposes someone to breast-cancer.
If one defective allele is inherited, the person may get breast cancer if the second allele becomes damaged in breast tissue cells.
Therefore individuals who have already inherited one faulty allele for BRCA1 are more susceptible to cancer through environmental damage.

Question 53

Explain how smoking and UV light causes cancer.

What happens if the tumour is not removed?

Answer 53

Carcinogens in tar lodge in bronchi and damage DNA in surrounding epithelial cells, causing cancer.
UV light damages DNA in skin cells.
Sometimes moles affected by UV can develop into a tumour.
If the tumour is not removed, cancer cells can spread to other organs, as they can be carried in the blood and lymphatic systems.

Question 54

Explain how a poor diet/ radicals and viral infections can cause cancer.

Answer 54

Radicals are from chemicals in the diet, environmental factors like UV or from the cell’s metabolism. It causes ageing and cancer via DNA damage. Fruit and veg are antioxidants that destroy radicals.
Viral infections can trigger cancer. Hepatitis can cause liver cancer. A virus’ RNA may even contain an oncogene which it has picked up from a host and transfers the oncogene to cells it infects.

Question 55

State the definition for the following:
tumour 
Metastasis
Malignant
Proto-oncogenes
Melanoma

Answer 55

Tumour= is an abnormal new growth of tissue.
Metastasis= cancer cells break away from the primary tumour and form in other organs.
Malignant= tumour made of cancer cells that can invade nearby tissue
Proto-oncogenes= normal genes that become oncogenes when mutated.
Melanoma= tumour of melanin forming cells, associated with skin cancer.

Question 56

What are epigenetic changes?

Answer 56

Epigenetic changes are chemical modifications to DNA or histones which regulate gene expression.
Epigenetic changes are not mutations because they don’t change the base sequence of DNA
epigenetic changes occur during development of an organism and are caused by environmental factors.
Many epigenetic changes are heritable- they can be passed on during mitosis or meiosis

Question 57

What are operons?

Answer 57

In prokaryotic cells, genes are found in groups called operons.
An operon is a group of genes that are all transcribed juntos because juntos they code for a specific metabolic pathway
They are useful because genes that code for a specific metabolic pathway can all be switched on or off

Question 58

What is the cytoskeleton?

Answer 58

The cytoskeleton is made out of proteins like microfilaments, microtubules, and intermediate filaments, which all provide structural stability.

The cytoskeleton is v dynamic, allowing the cell to change shape by selectively contracting and extending filaments. This is important in some cell functions like muscle contraction, cell division, cell movement

The cytoskeleton also helps structures within the cell move from one area to another.

Question 59

What is a cell filled with?

Answer 59

The cell is filled with organelles and intracellular fluid called cytosol, which contains ions like Na and K.

The cytosol and the organelles make up the cytoplasm of the cell.