Topic 3 - Voice of the Genome Flashcards
Compare and contrast prokaryotes and eukaryotes.
Bacteria and cyanobacteria (photosynthetic bacteria) together make up the prokaryotae kingdom. They are smaller than eukaryotes with diameters between 0.5 and 5 um whereas eukaryotes have diameters 20um or more. Prokaryotes do not contain membrane bound organelles whereas eukaryotes do. Smaller ribosomes in prokaryotes than in eukaryotes. Prokaryotes have a flagellum whereas eukaryotes do not. Prokaryotes also have circular DNA. Additionally, not all eukaryotes have a cell wall.
Describe the functions of the structures that are not always present in prokaryotic cells.
a. Plasmid – small circles of DNA
b. Capsules – A slimy layer on the surface for protection and to prevent dehydration.
c. Pili – thin protein tubes which allow bacteria to adhere to surfaces.
d. Flagellum – hollow cylindrical thread-like structure which rotates to move the cell.
What structures are present in all prokaryotic cells?
a. Infolding of the cell surface membrane – site of respiration.
b. Ribosomes which are smaller than in eukaryotes.
c. Circular DNA
d. Cell surface membrane
e. Cell wall (contains peptidoglycan, a type of polysaccharide and polypeptide combined.
f. Cytoplasm
What is the calculation for magnification?
Magnification = image size / actual size
How are proteins processed after being synthesised in our body?
a. Once transcription of DNA to mRNA, the mRNA leaves the nucleus, proteins made on ribosomes enter rough ER (endoplasmic reticulum), protein moves through the ER assuming three-dimensional shape en route.
b. Vesicles pinched off the rough ER contain the protein, vesicles from rough ER fuse to form the flattened sacs of the Golgi apparatus, proteins are modified within the Golgi apparatus, vesicles pinched off the Golgi apparatus contain the modified protein, the vesicles then fuse with the cell surface membrane releasing protein, such as extracellular enzymes.
Describe fertilisation.
a. If intercourse takes place at about the time of ovulation, sperm may meet the ovum in the oviduct. The sperm which contains a protein called antifertilizin are attracted to the ovum by chemicals released from it, a protein called fertilizin. The acrosome in the head of the sperm swells, fuses with the sperm cell surface membrane and releases digestive enzymes. These enzymes break down the follicle cells and zona pellucida of the ovum. This is called the acrosome reaction.
b. The acrosome is a type of lysosome. Lysosomes are enzyme-filled sacs found in the cytoplasm of many eukaryotic cells.
c. Once a sperm fuses with and penetrates the membrane surrounding the egg, enzymes released from lysosomes in the ovum cause the zona pellucida, to thicken, preventing any further sperm entering the egg. This is called the cortical reaction. The sperm nucleus that enters the egg fuses with the egg nucleus to produce a fertilised egg (zygote).
Where does meiosis occur and what important roles does it have?
a. Meiosis produces gametes with only half the number of chromosomes, called the haploid number (n) (23 in humans).
b. Meiosis occurs in the ovaries and testes of animals, and the ovaries and anthers of flowering plants.
c. Meiosis has two important roles.
i. Firstly, it results in haploid cells, which are necessary to maintain the diploid number after fertilisation.
ii. Secondly, it helps create genetic variation among offspring.
Describe independent assortment.
During meiosis only one chromosome from each pair ends up in each gamete. Either chromosome from each pair could be in any gamete. For example, an organism with six chromosomes, that is three homologous pairs XX, YY and ZZ, could form eight (2^3) combinations in its gametes.
Describe crossing over.
During the first meiotic division, homologous chromosomes come together as pairs and all four chromatids come into contact. At these contact points the chromatids break and rejoin, exchanging section of DNA between non-sister chromatids. The point where the chromatids break is called a chiasma and several of these often occur along the length of each pair of chromosomes, giving rise to a large amount of variation. There is no crossing over between the sex chromosomes during meiosis.
What is Gregor Mendel’s garden peas experiment in 1850?
He crossed pure breeding, homozygous, tall purple-flowered plants with short white-flowered plants. All of the offspring produced were tall with purple flowers. He went on to cross two of these plants and found that plants were produced showing all combinations of the characteristics: tall and purple, tall and white, short and purple, and short and white.
When are genes inherited independently?
genes are inherited independently only if they are on separate chromosomes or are far apart on the same chromosome.
What is the linkage of genes?
a. Any two genes with a locus on the same chromosome are linked together and will tend to be passed as a pair to the same gamete. This is known as linkage of genes.
b. The genes will only be separated and go into different gametes if crossing over happens between the pair of genes. If the two genes are very close together on the same chromosome, crossing over is very unlikely to happen between them. The two genes are said to be strongly linked and they will be inherited as a pair.
How many linkage groups are inside humans and how are chromosomes numbered?
a. Genes on a single chromosome make up a linkage group. In humans, there are 23 linkage groups because we have 23 pairs of chromosomes.
b. Chromosomes are numbered from the longest to the shortest, so we expect chromosome 1 to contain the most genes and chromosome 22 the fewest.
c. Chromosome 23 is the sex chromosome.
What is sex linkage?
a. Mammals, including humans, sex is controlled by the sex chromosomes.
b. Females are XX and males XY.
c. The Y chromosome contains genes that make a person male and very few other genes.
d. All the genes on the sex chromosomes are passed on with those that determine sex, they are sex linked.
How is red-green colour blindness sex linked and how is it inherited?
a. The gene loci for the three pigments found in the eye’s cone cells are on the X chromosome.
b. Cone cell pigments are needed for colour vision.
c. If one or more cone pigments is faulty or absent, the person will not be able to see colours normally: they will have some form of colour blindness.
d. Red-green colour blindness happens when there is a mutation in one of the cone pigment genes. This could happen (very rarely) when an egg or sperm is produced in meiosis.
e. The Y chromosome has no locus for the gene.
What is one cause of male infertility?
For the human zygote to develop, the gamete nuclei have to fuse and a chemical from the sperm cytoplasm is required to activate the fertilised cell. The chemical is a protein called oscillin. It causes calcium ions to move in and out of stores in the cytoplasm of the ovum. These oscillations of calcium ion concentration trigger the zygote to begin developing into an embryo. Oscillin is concentrated in the first part of the sperm to attach to the ovum and enters before the male nucleus, activating the ovum. It is though that low levels of oscillin in sperm may be linked to male infertility.
What happens in the S phase of the cell cycle and how long does it take?
a. In the S phase, the cell synthesises a complete copy of the DNA in its nucleus. It also duplicates a microtubule-organising structure called the centrosome. The centrosomes help separate DNA during the M phase.
b. The S and G2 phase of most cells remain relatively constant in duration.
How is DNA organised within chromosomes?
a. DNA winds around histone proteins.
b. DNA and histone proteins coil to form chromatin fibre.
c. Chromatin fibre attaches to a protein scaffold forming loops.
d. Folding the protein scaffolding produces the condensed chromosome structure seen during nuclear division.
Describe what happens in interphase.
During interphase, new cell organelles are synthesised, and DNA replication occurs. By the end of interphase, the cell contains enough cell contents to produce two new cells.
What happens in prophase?
a. During prophase, the chromosomes condense, becoming shorter and thicker, with each chromosome visible as two strands called chromatids. Apart from the occasional mutation, the two strands are identical copies of one another, produced by replication. They are effectively two chromosomes joined at one region called the centromere.
b. During prophase, microtubules from the cytoplasm form three-dimensional structure called the spindle. The centrioles move around the nuclear envelope and position themselves at opposite sides of the cell. These form the two poles of the spindle and are involved in the organization of the spindle fibres. The spindle fibres form between the poles. The widest part of the spindle is called the equator. The breakdown of the nuclear envelope signals the end of prophase and the start of the next stage.
What happens in metaphase?
During metaphase, the chromosomes’ centromeres attach to spindle fibres at the equator. When this has been completed the cell has reached the end of metaphase.
What happens in anaphase?
During anaphase, the centromeres split. The spindle fibres shorten, pulling the two halves of each centromere in opposite directions. One chromatid of each chromosome is pulled to each of the poles. Anaphase ends when the separated chromatids reach the poles and the spindle breaks down.
