2013 HSC COURSE

living tissue responsible to the bilateral movement of organic substances in plants from source to sink 

composed of: 1. sieve tube elements and compagnion cells linked end to end 2. sieve tube plates perforated with pores linked by plasmodesmata 

suggested with crick that DNA molecule was made up of 2 chains of nucleotides each in a helix by one going up and the other going down

realised that A - T pair held togethor by 2 hydrogen bonds was identical to G - C pair  - therefore these pairs of bases could serves as rungs on the twisting ladder of DNA

deduced that the matching base pairs of which there were similar amounts interlocked in the middle of the double helix to keep the distance between the chains constant 

Concluded that the DNA molecules was made up of 2 chains of nucelotides, bonded in a double helix shape with one going up and the other going down

Produced the "world's best" X ray diffraction images of DNA 

Extracted fine DNA fibers than ever before and arranged them in paralled bundles before studying reaction to humid conditions 

Found her images showed that the 'wet' form of DNA had the characteristics of a helix

X ray diffraction images became the basis of watsons and cricks conclusion 

Showed that the chains of nucleotides in DNA were in the shape of helixes - crucial to watsons and cricks conclusions 

Found DNA could exist in 2 forms depending on humidity of surrounding air

deduced that the phosphate part of DNA was on the outside 

Showed watson one of franklins X ray diffraction images giving vital information

Enabled the combination of Franklins images and Watsons and Cricks research leading to watsons and cricks conclusion on the structure 

Franklin's reluctance to share her works ultimately meant she was not directly credited for her work and the discovery of the structure was retarded 

Good collaboration between watson and crick helped find a quicker solution

for any particular trait the pair of alleles / factors each each parent seperate and only one allele / factor passes from each parent to an offspring 

different pairs of alleles are passed to offspring interpendant of one another

e.g. if a pea plant inherits purple flower its is no more likely to inherit yellow seeds 

• Two scientists are credited with the discovery of the role of chromosomes in 1902. They were the German scientist Theodor Boveri and the American microbiologist Walter Sutton.

• Boveri worked on sea urchins and showed that their chromosomes were not all the same and that a full complement was required for the normal development of an organism.

• Sutton worked on grasshoppers and showed that their chromosomes were distinct entities. He said even though they duplicate and divide they remain as a distinct structure. He associated the behaviour of chromosomes with Mendel's work on the inheritance of factors and concluded that chromosomes were the carriers of hereditary units.

• Together their work became known as the Sutton-Boveri chromosome hypothesis.

Meiosis is the process of division in which sex cells are produced(ie gamates)

In the process half the number of chromosomes are in each sex cell (compared to a normal cell)

occurs in the sex organs 

models the process of meiosis using jelly snakes to represent chromosomes   

cell with diploid number of 2 (2 pairs of 2 chromosomes) 1 pair short homologous 1 pair long homologous with each chromsome in the homologous pair a different colour

Chromosomes were doubled keeping colours consistant (copy attached to original at centromere) 

crossing over was modelled between homologous chromosomes by breaking off pieces from the homolougous chromatid and rejoining to the other homologous chromatid

random segregation was modelled as each homologous pair lined up at the equator in random order 

The homologous chromosomes then moved away from each other to the poles of the cell by the spindle

cytokinesis occurs 

Chromosomes are once again drawn to the equator and then the chromatid are seperated drawn by the spindle to the poles 

cytokinesis 

4 cells each with 2 seperate chromosomes 

Colours of the snakes helped understand the idea of homologous chromosomes and made crossing over clear as well as the random segregation of chromosomes (different possibilities)

The snakes being soft and sticky demonstrated crossing over clearly 

Moving the snakes around to simulate movement in meiosis helped to understand the dynamic nature of the process 

The snakes could be resized to make chromosome pairs different sizes 

• Chromosomes are made of DNA. Genes are coded within the DNA on the chromosomes. Meiosis in four genetically different sex cells (due to crossing over and random segregation) that are haploid, (ie contain half the chromosome number of the original cell) thereby creating 4 possibilities for the inheritance of genes

Gamete formation results in the halving of the chromosome number (n) (diploid to haploid) and sexual reproduction results in combining gametes (haploid to diploid) to produce a new diploid organism (2n).

The processes involved in forming this new organism result in variability of the offspring as not only does 2 different genetic makeups combine through sexual reproductioon, but in gamete formation each sex cell is also genetically different each other due to random segregation and crossing over during meiosis

aim: to demonstrate the effect of the environment on the phenotype of bean sprouts 

hypothesis: The different environmental condition will result in different phenotypes 

risk: spilt water is a slipping hazard and may cause injury. As such clean up any split water immeadiatly 

materials 100 x bean sprouts 10 x plastic contrainer 1x cotton wool 1 x 1L water 1x light impermiable sheet 

method: 1x place a layer of cotton wool into each of the plastic containers 2. soak cotton so that it is damp 3. place 10 bean sprouts into each container equally spaced 4. store 5 containers under the light impermiable sheet and 5 in a light abundant area 5. leave for 2 days and return 6. record results 

1. DNA double helix unwound by helicase enzyme 

2. DNA unzips to form two seperate strands 

3. Complementary nucleotides are brought over by DNA enzyme polymerase and form hydrogen bonds with the single strands resulting in two identical strands of DNA

4. DNA double helix rewinds 

takes place during interphase in preparation for nuclear division that occurs during meiosis or mitosis 

Ensures daughter cells receive a copy of DNA from parent cells in asexual reproduction and mitosis and half the genetic information in meiosis

Semi conservative (each new double helix has one original and one new strand)

DNA carries the instruction for making a polypeptide and therefore a protein 

RNA is used to transcribe the message from DNA (as it is small enought to fit through the nuclear pore to the ribosome) it does so through helicase enzyme unwinding the enzyme, and RNA polymerase building a complementary strand of mRNA

The ribosomes translates the DNA sequence 3 bases at a time and tRNA (transfer RNA) molecule brings over the corrosponding amino acid (the amino is based on the mRNA condon) 

Peptide bonds form between neighbouring amino acids

tRNA molecule is released back into the cytoplasm

Chain of amino acids form a polypeptide chain

sequence stops when ribsosome reaches a stop sequence and starts again when it reaches a start condon 

DNA ---> transcription ---> RNA ---> translation ---> polypeptide 

Polypeptides are the basic units of proteins 

Sometimes more than one polypeptide chain is needed to create a protein (and therefore more than one gene may be needed to create a protein)

A chain of amino acids 

• Any change in the base sequence in DNA by mutations may result in different polypeptides being produced and therefore a new allele
• if the mutation occurs in the sex cells of the organism the mutated code may be passed off to offspring
• The offspring may therefore have a new allele/s from the changed protein/s depending on the effect of the mutation

depending on types of mutations mutations may have:

no effect - as mutation produces the same amino acid 

neutral effect - eye colour

harmful effect - e.g. sickle cell anaemia 

beneficial effect - e.g. sickle cell anaemia immunity to HIV

Changes in the number and/or structure of entire chromosomes 

may occur during meiosis when homologous chromosomes dont seperate properly 

e.g. down's syndrome (trisome 21)

inheritance from parents (if mutation occurs in sex cells)

environmental damage (radiation)

mistakes when DNA is compied 

insecticide DDT was used to eradicate maleria carrying mosquito 

however widespread use cause resistance to occur arising from a mutation in a single genen DDT-R  (occured in the sex cellsand was passed on)

A mutagen is a natural or human-made agent (physical or chemical) which can alter the structure or sequence of DNA.

Mutagens can be carcinogens (cancer causing) or teratogens (birth defects causing).