Topic 3 - Voice Of The Genome Flashcards
(55 cards)
1
Q
What are the 12 organelles in an animal cell?
A
- Cell membrane
- Rough er
- Smooth er
- Lysosomes
- Centrioles
- Nucleus
- Nucleolus
- 80s ribosomes
- Golgi
10.mitochondrion - Nuclear pore
- Nuclear envelope
2
Q
What do the ReR and SeR do?
A
- Covered in ribosomes, involved in protein trafficking and is membrane bound.
- Does lipid synthesis,it makes new membrane
3
Q
What does the mitochondrion do?
A
It is involved in aerobic respiration, has circular DNA chromosomes, outer membrane is smooth and inner membrane is folded into cristae. Also contains 70S ribosomes.
4
Q
What does the Golgi do?
A
Is a series of flattened membrane vesicles, it sorts and modifies proteins.
5
Q
What do lysosomes and centrioles do?
A
- Membrane bound vesicles that contain digestive enzymes
- Hollow cylinders made of microtubules that sit at right angles and organise fibres during cell division.
6
Q
What does the nucleus and nucleolus do?
A
- MRNA leaves out of its pores.
- Transcription takes place there.
7
Q
What are the 80s ribosomes for?
A
Protein synthesis
8
Q
What are the 9 organelles that make up prokaryotic cells?
A
- Pili = not in all bacteria, allow plasmids to be passed between bacteria
- Slime capsule = protects from dehydration
- Cell wall = made up of peptidoglycans (sugars and amino acids)
- Cell membrane
- Mesosome = infolding of cell membrane, existence is controversial
- Flagellum = not in all bacteria, rotates for movement
- Nucleoid = bacterial chromosomes, circular molecule of DNA, DNA is not wrapped around proteins
- Plasmids = small circles of DNA, contains extra genes.
- 70S ribosomes = for translation, smaller than Eukaryotic ones
9
Q
What are 2 similarities between prokaryotic and eukaryotic cells?
A
- Both have organelles
- Both cell membranes are made up of phospholipid bilayer which controls passage of substances across exchange surfaces.
10
Q
What are 4 differences between eukaryotic and prokaryotic cells?
A
- Prokaryotic cells make up single celled organisms whereas eukaryotic cells make up complex organisms.
- Eukaryotic cells are larger and more complex whereas prokaryotic cells are smaller (0.1-5 micrometres)
- Eukaryotic cells contain membrane bound structures whereas prokaryotic dont.
- Prokaryotic cells use binary fission whereas eukaryotic cells use mitosis and meiosis.
11
Q
What are the 4 components of the sperm cell?
A
- Flagellum = rotates so sperm can swim to egg
- Mitochondria= spiral shaped to provide energy for flagellum
- Haploid nucleus
- Acrosome = modified lysosome, contains digestive enzymes to digest zona pollucida
12
Q
What are the 6 components of an ovum?
A
- Follicle cells from ovary = release chemicals to attract sperm
- Zona pollucida = jelly like layer around egg
- Cell membrane
4.lysosomes = around the edge and contain enzymes which harden zona pollucida following fertilisation. - Lipid droplets = provide nutrients to zygote
- Haploid nucleus
13
Q
What are 3 adaptations of the ovum?
A
- Egg is much larger than sperm as it contains nutrients and so sperm can find it easily.
- Follicle cells attract sperm and provide protective coating
- Jelly like glycoprotein layer, zona pollucida, forms in-penetrable barrier after fertilisation.
14
Q
What are the 8 steps of fertilisation?
A
1.sperm cells attracted to ovum by the chemicals released from the follicle cells.
2. Sperm cell attaches to follicle cells and chemicals from follicle cells trigger the acrosome reaction.
3. Acrosome swells and fuses with sperm cell membrane.
4. Enzymes released from acrosome digest through follicle cells and zona pollucida.
5. Sperm cell fuses with ovum cell membrane
6. Sperm nucleus enters ovum
7. Cortical reaction takes place where enzymes are released from lysosomes which harden the zona pollucida to prevent further fertilisation.
8. Sperm and ovum nuclei fuse.
15
Q
What are the 6 steps of protein trafficking?
A
- DNA is transcribed into mRNA, the mRNA leaves nucleus through the nuclear pore.
- MRNA binds to a ribosome on the Rough er and is translated into the lumen of the er.
- Polypeptide chain is folded into a protein and packaged into a vesicle
4.vesicle buds off er and fuses with Golgi. - Proteins are modified by adding carbs and sorted by destination.
- Vesicle buds off Golgi and fuses with cell membrane and released outside of the cell.
16
Q
Which type of cell division produces gametes?
A
Meiosis
17
Q
What is meiosis?
A
Type of cell division that produces gametes with a haploid number of chromosomes.
18
Q
What are the 3 steps of meiosis?
A
- DNA replication, each chromosome is replicated.
- Meiosis 1, where the homologous chromosomes line up and divide into 2 daughter cells each with only one homologous pair.
- Meiosis 2, where the 2 divide into 4 haploid daughter cells, each with only one chromatid from each homologous pair.
19
Q
How do you work out the number of all the possible chromosome combinations?
A
2^n n= number of pairs of chromosomes.
20
Q
How does meiosis provide genetic variation?
A
By crossover/recombination and independent assortment.
21
Q
What is crossover?
A
It takes place in meiosis 1.
Homologous chromosomes line up and have points where they are in contact which are called chiasmata. Where the chiasmata are, the chromatids break off and switch places.
22
Q
Definition of locus?
A
Location of a gene on a chromosome
23
Q
What does linkage refer to?
A
Linkage refers to how alleles of genes on the same chromosome are more likely to be in the same gamete after meiosis so are inherited together.
24
Q
Why do 2 genes that are more linked have a higher chance of being inherited together?
A
This is because the closer the loci of two genes on a chromosome, the less likely a crossover will occur between them so they are more linked.
25
What is independent assortment?
It is a random process where either chromosome from each pair could end up in any gamete as it depends on which side the chromosome is.
26
What is sex linkage?
Genes that are only on the x or Y chromosomes.
27
Why are recessive genes on X chromosome more likely to exhibit their phenotype in males?
Because there is no other allele on the Y chromosome to dominate it.
28
What is mitosis and what is it needed for?
Mitosis is a type of cell division producing 2 genetically identical daughter cells with exact copies of DNA. It is needed for growth of multicellular organisms, repairing damaged tissues and for asexual reproduction.
29
What are the 3 parts of the cell cycle and describe each one?
Interphase:
- Intense and organised activity
- Cells synthesise new membrane, organelles and DNA
- DNA synthesis only happens in S though
- Interphase is a different length for different cells e.g human embryos do not have interphase for the first few divisions and the embryo divides into smaller cells with each division making it the fastest dividing cell.
1. G1= can take weeks, months or even years
2. S= synthesis of DNA, where DNA replication occurs.
3. G2= Further growth and checks the DNA for errors.
4. Nuclear division (mitosis) which separates the DNA.
5. Cytoplasmic division which separates the cytoplasm and 2 new cells are produced.
30
What are the 4 stages of mitosis?
Prophase, metaphase, anaphase and telophase.
31
What are the steps of each mitosis stage including interphase?
Interphase:
- DNA is replicated doubling the genetic material
- Organelles are replicated
- ATP content is increased
Prophase:
1. The nuclear envelope breaks down
2. The chromosomes condense becoming shorter and fatter
3. Centrioles migrate to poles at either end of the cell
Metaphase:
1. Chromosomes line up along the centre of the cell
2. Spindle fibres connect the chromosomes to the centrioles by their centromeres
Anaphase:
1. Centromeres divide, separating each pair of sister chromatids
2. Spindle fibres shorten pulling the chromatids to either end of the cell.
Telophase:
1. Nuclear envelope reforms around the 2 groups of chromosomes forming 2 new nuclei
2. Chromosomes start to decondense
3. Cytokinesis takes place resulting in 2 new genetically identical daughter cells with identical genetic makeup to original cell.
32
What are the 4 points about cell differentiation and stem cells?
1. Multicellular organisms are many up of many different types of cells e.g tissue cells, liver cells and WBC’s.
2. All of these specialised cell types come from stem cells.
3. Stem cells divide by mitosis to then become new cells which become specialised. This process is called differentiation.
4. The ability of a stem cell to differentiate is called potency.
33
What are the 3 types of cell potency?
1. Totipotency= The ability to produce all cell types including all specialised cells in an organism and extra embryonic cells (including placenta cells and umbilical cord cells).
2. Pluripotency= the ability of a stem cell to produce all specialised cells types except for extra embryonic cells as the genes for these have been inactivated.
3. Multipotency= these are stem cells which can only differentiate into a limited number of stem cells. These occur in adult stem cells.
34
What are the 3 types of adult stem cells?
1. Haematopoetic stem cells (bone marrow)- differentiates into red blood cells, b cells or T cells.
2. Skin stem cells
3. Neural stem cells.
35
What is the pathway of getting stem cells from a zygote?
1. Zygote divides by mitosis several times to produce a bundle of totipotent cells.
2. These become blastocysts which consist of fluid filled cavity, inner mass/embryonic stem cells and trophblast layer which becomes the placenta.
3. The inner mass/embryonic stem cells are retrieved and are pluripotent.
4. They differentiate to become cardiac tissue, digestive tissue and nervous tissues.
36
Why does specialisation occur?
Specialisation occurs due to the selection of proteins present in a cell. Genes can be switched on or off which is called differential gene expression and the changes in gene expression as a cell specialises determines the final characteristics within the cell.
37
How do stem cells become specialised? (5)
Through differential gene expression
1. All stem cells contain the same genes but not all the genes are expressed as not all the genes are active.
2. Under the right conditions, genes are either activated or inactivated.
3. MRNA is then only produced from the active genes.
4. Active mRNA is then translated into proteins which modify the cell as they control the cell structure and cell processes.
5. These changes caused by the proteins produced, cause the cell to become specialised which is very difficult to reverse and so the cell stays specialised.
38
How can gene expression be controlled?
Transcription factors, histone proteins or DNA methylation
39
What is the definition of a transcription factor and the 2 types?
Transcription factors= proteins that control gene expression by stimulating or inhibiting the transcription of target genes. They are made in the cytoplasm and move to the nucleus.
Activators= promote transcription of genes by interacting with RNA polymerase and allowing it to bind to DNA.
Repressors= prevent transcription of genes by stopping RNA polymerase from binding to DNA.
40
What are the 4 steps of control of gene expression by transcription factors?
1. Gene expression can be controlled by altering the rate of transcription e.g increased transcription produces more mRNA which produces more proteins.
2. Transcription factors control this by using repressors and activators.
3. In Eukaryotes like plants and humans, the transcription factors bind to specific DNA sites that are near the start of the target genes. However, in prokaryotes, the transcription factors bind to persons.
4. Operons are sections of DNA that include clusters of structural genes that are transcribed together as well as control elements and sometimes regulatory genes.
41
What are control elements?
Control elements= include promotors which are sequences of DNA located before structural genes which RNA polymerase binds to, operators are sequences of DNA that transcription factors bind to.
42
What are the 2 points about the lac operon?
1. E.coli are a bacterium that respire glucose but can use lactose when glucose is not present.
2. The genes that produce enzymes to respire the lactose are on an operon called the lac operon which produced B-galactosidase an enzyme which digests lactose into glucose and galactose.
43
What happens at the lac operon when lactose is not present? (3)
1. The regulatory gene produces the lac repressor which is a transcription factor which binds to the operator site.
2. The RNA polymerase is now unable to bind to the promotor region, blocking transcription.
3. So no B-galactoside as produced.
44
What happens at the lac operon when lactose is present? (2)
1. When lactose is present, it binds to the repressor which changes its shape meaning it can no longer bind to the operator site.
2. RNA polymerase is now able to bind to the promotor region allowing transcription to begin and producing B-galactosidase.
45
How can epigenetics control gene expression?
Epigenetic control can determine whether genes are expressed, altering phenotype. Epigenetic control does not alter the DNA base sequence, it works by attaching or removing certain chemical groups to and from DNA.
Epigenetic changes occur in response to a stimulus such as light or a signal from another cell however they can also be due to environmental changes such as change in pollution, smoking or food availability.
46
What is the definition of the epigenome?
The epigenome is all of the chemical modifications which affect transcription and DNA.
47
What is the definition of epigenetic markers?
Epigenetic marks are the chemical groups such as acetyl or methyl groups which modify DNA or histone proteins.
48
What is chromatin?
Chromatin is the combination of histone proteins and DNA, it is only found in eukaryotes and can be more or less condensed and how condensed it is influences the accessibility of DNA and transcription.
49
How are histone proteins modified including addition and removal of acetyl groups? (5)
1. Histone proteins are modified by the addition or removal of acetyl groups.
2. When histones are acetylated, chromatin becomes less condensed as the acetyl makes the histone tails less positively charged which weakens the intermolecular bond between the negatively charged sugar phosphate backbone.
3. This means the regulatory regions are exposed and therefore transcription factors are able to bind to them and transcription can take place.
4. When acetyl groups are removed, the chromatin becomes highly condensed as the histone tails become more positively charged allowing the DNA to bind much more tightly.
5. This prevents the access of transcription factors so the gene is switched off as it cannot be transcribed.
50
How does increased methylation repress genes? (4)
1. DNA becomes methylated on cytosine bases.
2. Methylation of DNA suppresses the transcription of the affected gene by inhibiting the transcription factors and other enzymes needed for transcription like RNA polymerase from binding.
3. This means that the gene is now switched off or repressed permanently.
4. This gene will remain methylated and switched off in any subsequent cells.
51
How are epigenetic changes passed on?
1. When cells divide and replicate, epigenetic changes to the expression of genes may be passed down to subsequent daughter cells e.g methyl groups are usually removed during gamete production but some escape this process and can end up in sperm or egg cells.
2. This means that certain genes activated or inactivated in the original cell, will also be activated or inactivated in the daughter cells.
3. If the epigenetic changes occur due to a change in the environment, then the daughter cells will be equipped to deal with the changed environment in the same way as the original cell was.
52
What are the 2 types of variation?
Continuous variation= individuals within a population fall within a range, there are no distinct categories for example height and mass.
Discontinuous variation= when there are 2 or more categories and people only fall into one e.g blood type.
53
What is monogenic/monohybrid inheritance?
Characteristics that are only controlled by one gene.
54
What is polygenic inheritance?
Characteristics which are controlled by a number of genes at different loci usually showing continuous variation.
55
What if the expected ratios for monohybrid inheritance and for dihybrid inheritance?
3:1
9(DD):3(DR):3(RD):1(RR)
