Topic 2

Question 1

What is cell theory?

Answer 1

All living organisms are made of cells
Cells are the smallest unit of life
Cells arise from pre-existing cells.

Question 2

how are organ systems made?

Answer 2

Organelles -> cells -> tissues -> organs -> organ systems

Question 3

What are prokaryotic cells?

Answer 3

These are organisms without a nucleus. E.g Bacteria.

They divide by binary fission.

Question 4

What are the structures in prokaryotic cells?

Answer 4

70s Ribosomes: the site of protein synthesis.

Cell Wall: peptidoglycan layer that protects and maintains cell shape. Bacterial cell walls are either gram positive or gram negative.

Nucleoid: region containing a single, free, circular strand of DNA.

Pili: protein filaments that facilitate adhesion and conjugation.

Plasma membrane: phospholipid layer with embedded proteins that controls the movement of materials in and out of the cell.

Plasmid: an independent, small, circle of DNA.

Flagella: elongates, relatively inflexible. Corkscrew-shaped structures resembling pili that can be rotates to move the cell.

Question 5

What is the structure of a gram positive cell wall

Answer 5

THICK peptidoglycan layer: a polypeptide and polysaccharide mix made from cross linking to maintain strength and shape.

Periplasmic space

Plasma membrane

Cytoplasm.

Susceptible to penicillin and lysozyme (enzyme) as they interfere with inter-peptide linkages in peptidoglycan.

Will stain violet as thick peptidoglycan layer absorbs crystal violet.

Question 6

What is the structure of a gram negative cell wall?

Answer 6

Lipopolysaccharide outer membrane

Periplasmic space

THINNER peptidoglycan layer:

Periplasmic space

Plasma membrane

Cytoplasm.

Resistant to penicillin and lysozyme (enzyme). Antibiotics must target prokaryotic protein synthesis.

Will not absorb crystal violet as protected by lipopolysaccharide outer membrane.

Question 7

Function and structure of nucleus and nucleolus in eukaryotic cells.

Answer 7

A double nuclear membrane containing pores, known as the nuclear envelope. Chemicals pass in and out through these pores so the nucleus can control events in the cytoplasm. Inside NE are nucleic acids + protein. In nucleus is nucleolus, an extra dense area of pure DNA and Protein.

Question 8

Function and structure of 80s ribosomes in eukaryotic cells.

Answer 8

Where protein synthesis takes place. Made up of ribosomal RNA and protein.

Question 9

Function and structure of RER in eukaryotic cells.

Answer 9

The outside of endoplasmic reticulum is covered with 80s ribosomes. The ribosomes makes proteins and the RER isolates and transports them.

Question 10

Function and structure of SER in eukaryotic cells.

Answer 10

SER is NOT covered with ribosomes. It synthesises and transports steroids and lipids.

Question 11

Function and structure of mitochondria in eukaryotic cells.

Answer 11

Site of respiration. Inner and outer membrane. They have their own genetic material so when cell divides, they replicate themselves under the control of the nucleus. Inner membrane folded to form cristae, giving large surface area.

Question 12

Function and structure of centrioles in eukaryotic cells.

Answer 12

involved in cell division. When cell divides, the C pull apart to produce a spindle of microtubules that move the chromosomes. Made up of a bundle of 9 tubules.

Question 13

Function and structure of Lysosomes in eukaryotic cells.

Answer 13

Dark, spherical bodies that contain a mix of digestive enzymes. They fuse with each other, or membrane bound vacuole containing food or obsolete organelle. The enzymes break down the contents.

Question 14

Function and structure of Golgi Apparatus in eukaryotic cells.

Answer 14

Gathers simple molecules and combine them to make more complex molecules. The big molecules are then packaged in vesicles and either stored or sent out of the cell. It also build lysosomes.

Question 15

Function and structure of Cell Wall in eukaryotic cells.

Answer 15

Made up of insoluble cellulose. Consists of several layers; middle lamella is made of pectic (acts like glue to hold the cell together), secondary cell wall - cellulose microfibres laid densely and at different angles to each other to create strong and rigid structure.

Question 16

Function and structure of Chloroplast in eukaryotic cells.

Answer 16

site of photosynthesis

Question 17

Function and structure of Vacuole and Tonoplast in eukaryotic cells.

Answer 17

A fluid filled space inside the cytoplasm, surrounded by a specialised membrane called the tonoplast, which controls the movement of substances in and out of the vacuole through protein channels and carrier systems. Vacuole filled with cell sap, causes H2O to move into cell = presses cytoplasm against wall = turgid.

Question 18

Magnification equation

Answer 18

Image size = actual size x magnification

Question 19

mm to um conversion

Answer 19

There are 1000 um in a mm.

Question 20

DNA Viruses

Answer 20

DNA VIRUSES:
The genetic material is DNA. The viral DNA acts directly as a template for both new viral DNA and for the mRNAs needed to induce synthesis of viral proteins.
E.g. smallpox virus and some bacteriophages such as λ phage.

Question 21

RNA viruses

Answer 21

RNA VIRUSES:
RNA viruses do not produce DNA. The majority of RNA viruses contain a single strand of RNA and are known as ssRNA viruses.
Positive ssRNA viruses have RNA that can act directly as mRNA and can be translated at the ribosomes. E.g. tobacco mosaic viruses
Negative ssRNA viruses cannot be directly translated. The RNA strand must be transcribed before it is translated at the ribosomes. E.g. Ebola.

Question 22

RNA Retroviruses

Answer 22

RNA RETROVIRUSES:
They have a protein capsid and a lipid envelope. The single strand of RNA directs the synthesis of reverse transcriptase (enzyme). This goes on to make DNA molecules corresponding to the viral genome. This DNA is then incorporated into the host cell DNA and used as a template for new viral proteins and a new viral RNA genome. E.g. HIV

Question 23

DNA Virus Replication

Answer 23

DNA Virus Replication
There are two different routes of infection once a virus is inside a host cell:
LATENCY – THE LYSOGENIC PATHWAY
Some DNA viruses are non-virulent when they first get inside the host cell. They insert their DNA (provirus) into the host’s DNA so it is replicated every time the cell divides. mRNA is not produced from the Viral DNA. The Virus does not affect the host cell at this stage. During this period of lysogeny the virus is said to be latent. Under certain conditions (host is damaged) lysogenic viruses are activated.
LYTIC PATHWAY
viral DNA is replicated independently of the host DNA. Mature viruses are made and eventually the host cell bursts releasing virus particles to invade other cells. The virus is virulent and the process of replicating and killing cells is known as the lytic pathway.

Question 24

Retrovirus replication/life cycle

Answer 24

Retroviruses
Retroviruses have a complex life cycle.
They have viral RNA as their genetic material.
It cannot be used as mRNA, but is translated into DNA by the viral enzyme reverse transcriptase in the cytoplasm of the cell.
The viral DNA passes into the nucleus of the host cell where it is inserted into the nucleus of the host cell and hence its DNA.
Host transcriptase enzymes then make mRNA and new viral RNA.
New viral material is synthesised and new viral material leaves the cell.
The host cell functions as a virus making factory and the viruses infect other cells.
E.g HIV

Question 25

Treatment of viruses

Answer 25

Antiviral treatments target virus replication:
target the receptors by which virus recognize their host cells.
Target the enzymes that translate or replicate DNA or RNA.
Inhibit the protease enzymes that enable new virus particles to bud from host membranes.
Preventing the spread of viral diseases e.g. Ebola:
rapid identification
nursing in isolation
preventing transmission from one individual to another
sterilizing/disposing of equipment
use of protective clothing by workers
identifying contacts

Question 26

Eukaryotic cell cycle

Answer 26

Cell cycle is a regulated process of three stages, (interphase, mitosis and cytokinesis) in which cells divide into two genetically identical daughter cells.
Interphase is the period between active cell divisions when cells increase their size and mass, replicate their DNA and carry out normal metabolic activities.
Mitosis is the process by which a cell divides to produce two genetically identical daughter cells.
Cytokinesis is the final stage of the cell cycle before it enters interphase again. it is the division of the cytoplasm at the end of mitosis to form two independent genetically identical cells.

Question 27

How is the cell cycle controlled?

Answer 27

In multicellular organisms, the cell cycle is repeated very frequently. But once the organism is mature, it may stop or slow down in some tissues.
The cell cycle is controlled by a number of different chemical signals made in response to different genes. This control is brought about at a number of different checkpoints where the cell cycle moves from one phase to the next. The controls chemicals are small proteins called Cyclins.
Cyclins build up and attach to enzymes called cyclin dependent kinases (CDKs). The Cyclin/CDK complex phosphorylates other proteins, changing their shape and bringing about the next stage in the cell cycle.
e.g the phosphorylation of some proteins in the nuclear membrane, which leads to the breakdown of the nuclear membrane structure during cell division.

Question 28

Spindle Microtubule definition

Answer 28

Spider like projections that attach centriole to centromere

Question 29

Chromosome definition

Answer 29

DNA molecule combined with histone protein

Question 30

Sister chromatids definition

Answer 30

newly replicated chromosome (from molecular duplication to time pf separation in Anaphase)

Question 31

Centromere definition

Answer 31

point at which two sister chromatids are joined

Question 32

Centriole definition

Answer 32

organelle that helps to organise microtubules in cell division. one at each pole of cell.

Question 33

Supercoiling definition

Answer 33

Repeated coiling of chromosomes so they become short and fat. (And visible under high of microscope)

Question 34

Stages of Mitosis

Answer 34

Mitosis is the process by which a cell divides to produce two genetically identical daughter cells. Mitosis occurs for growth, tissue repair and asexual reproduction.

Prophase: The chromosomes are coiled up and consist of two daughter chromatids joined by the centromere. The nucleus breaks down.

Metaphase: A spindle of overlapping protein microtubules form. The chromatids line up on the metaphase plate.

Anaphase: The centromeres split, so chromatids become new chromosomes. They are moved to the opposite poles of the cell, centromere first, by contractions of the microtubules of the spindle.

Telophase: The nuclear membrane forms around the two sets of chromosomes. The chromosomes unravel and the spindle breaks down.

Question 35

Meiosis:

Answer 35

Meiosis results in haploid gametes. It is responsible for genetic variation.

Prophase 1:
Each chromosome appears in the condensed form, with two chromatids. Homologous pairs of chromosomes associate with each other. Crossing Over occurs.

Metaphase 1: The spindle forms and the pairs of chromosomes line up on the metaphase plate

Anaphase 1: The centromeres do no divide. One chromosomes from each homologous pair moves to each end of the cell. As a result the chromosome number in each cell is half that of the original.

Telophase 1: The nuclear membrane reforms and the cells begin to divide. In some cells this continues to full cytokinesis and there may be a brief or prolonged interphase. During interphase there is no further replication of DNA.

Prophase 2: New spindles form

metaphase 2: The chromosomes, still made up of pairs of chromatids, line up on the metaphase plate.

Anaphase 2: The centromeres now divide and the chromatids move to the opposite ends of the cell.

Telophase 2: Nuclear envelopes re-form, the chromosomes return to their interphase state and cytokinesis occurs, giving four haploid daughter cells.

Question 36

how does meiosis lead to genetic variation?

Answer 36

Crossing over (recombination): large multi-complexes ‘cut and join’ bits of the maternal and paternal chromatids together. The points where the chromatids break are called chiasmata. 
Independent assortment (random assortment): the chromosomes derived from the male and female parent are distributed into the gametes at random.

Question 37

Chromosome mutations

Answer 37

Translocation: a mutation in which part of one chromosome breaks off and rejoins to another completely different chromosome.

Non-dijunction: members of a pair of chromosomes fail to separate during the reduction division of meiosis, resulting in one gamete with two copies of a chromosome and one gamete with no copies.
Polysomy: a cell contains three or more of one type of chromosome. E.g Down’s syndrome is trisomy 21.
Monosomy: when only one member of a pair of chromosomes is present in a cell. E.g Turners syndrome.

Question 38

Spermatogenesis

Answer 38

The production of sperm:

1. Primordial gem cells on basement membrane undergo mitosis to form 1 spermatogonia and a primordial gem cell.
2. Spermatogonia undergoes growth to form primary spermatocyte.
3. Meiosis 1 occurs to form two secondary haploid spermatocytes.
4. meiosis 2 gives 4 haploid spermatids.
5. Spermatids differentiate into spermatozoa (sperm cells)

Question 39

Oogenesis

Answer 39

The production of egg cells:

1. primordial gem cell undergoes mitosis to form 1 oogonia and a primordial gem cell.
2. Growth to form primary oocyte. This takes place in gestation. Primary oocytes are arrested in Prophase 1
3. Afer puberty 1 primary oocyte completes meiosis 1 each cycle to form a secondary oocyte and a polar body which degenerates.
4. During ovulation, 1 secondary oocyte is release and is arrested in prophase 2, unless fertilisation occurs.
5. if fertilisation occurs, the secondary oocyte divides to form a haploid ovum before becoming a diploid zygote .

Question 40

Fertilisation

Answer 40

1. sperm approaches the egg.
2. Whilst sperm are swimming, their acrosome regions matures .
3. Many sperm cluster around the secondary oocyte triggering the acrosome reaction. ( Enzymes digest the follicular cells and zone pellucid of the secondary oocyte)
4. One sperm will reach and fuse with the plasma membrane of the oocyte.
5. INSTANTLY:
   - secondary oocyte completes meiosis 2, forming an ovum and polar body.
   - ion channels in the vum open and close so the inside of the cell beocomes positively charges, temporary blocking entry of other sperm.
6. Cortical reaction occurs: cortical granules in ovum are exocytosed. This makes the zone pelucia permanently impenetrable as it becomes hard and thick.
7. make and female chromosomes group together to form a diploid zygote.

Question 41

Embryonic development:

Answer 41

1. the zygote is totipotent.
2. Cleavage occurs. The cells divide repeatedly without interphase between divisions.
3. This happens as the embryo traveled down the oviduct.
4. the resulting sphere of small cells after 5-6 days is known as a blastocyst.
5. the outer layer forms the placenta, the inner mass is now pluripotent.
6. the Blastocyst will implant in the endometrium 7 days after fertilisation.

Question 42

Microgametogenesis:

Answer 42

1. the anthers of angiospermophytes contain four pollen sacs, where pollen grains develop.
2. a diploid microspore mother cell divides by mitosis to form four haploid microspores.
3. The nucleus undergoes the first mitotic division to form a pollen grain that contains two haploid nuclei. The tube nucleus and generative nucleus.
4. The generative nucleus undergoes a second mitotic division to form two male gametes.

Question 43

megagametogenesis:

Answer 43

1. the ovule in angiospermaphytes contains a diploid megaspore mother cell.
2. this divides by meiosis to form 4 haploid cells. Tree cell degenerate.
3. The megaspore undergoes three mitotic divisions to form a multi nuclei structure called the embryo sac.
4. Cell walls begin to form and divide the structure into 3 antipodal cells, 2 synergies, 1 egg cell and 2 polar nuclei.

Question 44

Pollination and double fertilisation

Answer 44

1. the transfer of mature pollen to a receptive stigma.
2. Pollen tube grows down the style due to the release of digestive enzymes. It enters the embryo sac through the micropyle.
3. haploid sperm nuclei travel downwards through one synergic (which degenerates)
4. One sperm nuclei fuses with the egg to produce a diploid zygote. one sperm nucleus fuses with the two polar nuclei. This produces a triploid endosperm which is used as a food source.