3.16 DNA and Genetic Information

Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C ) with guanine (G)

Chromosomes are likely to contain thousands of genes
Position on it a gene loci
Expanding a gene loci -> double helix

Double helix
Parallel
Expanding small section holding double helix together -> Helixes

Helixes are called sugar-phosphate backbone

Source: http://ghr.nlm.nih.gov/handbook/illustrations/dnastructure.jpg

Centre - group of molecules called bases
(4 types of base - adenine, thymine, cytosine, guanine)
Base pairs: A-T and G-C

Example of gene - ACTGAACCAG
Order of the bases -> The order is a gene

Nucleus - Order of bases (ACTG)
- Number of bases

Source:  http://www.youtube.com/watch?v=CEBmnfLWDQs

Gene (nucleus) -> Protein (cytoplasm) -> Characteristic

A gene is the order of the bases on one side of the helix

3.15 Genes

Understand that a gene is a section of a molecule of DNA

Source:  http://www.youtube.com/watch?v=-GPZCggg2lA

DNA - double helix shape

A section of DNA is called a gene
Gene carries information which forms the characteristic of organism
e.g. blood group, petal colour, etc. (different genes for different characteristics)

- Genes are located in the nucleus
- Information is passed to the cytoplasm
- Information is transformed into protein (inside cytoplasm)

Information flow:
Gene (nucleus) -> Protein (cytoplasm)

3.14 Chromosomes

Recall that the nucleus of a cell contains chromosomes in which genes are located

Chromosomes - Genetic information within a cell in the nucleus

1. Chromosome composed of molecule called DNA
- takes shape of double helix

Sections of DNA are called genes
- 1 chromosome can have thousands of genes

Source: http://www.elmhurst.edu/~chm/vchembook/images/580dna.gif

Each gene carries information for construction of protein
Protein gives characteristic associated with gene (e.g. blood group)

DNA (Gene) -> Protein -> Characteristic

2. Different organisms have different numbers of chromosomes
e.g. Cat 38, Chicken 78, Chimp 42, Human 46 (chromosomes per cell)

3. Homologous pairs - genes operating in pairs

Source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiV4AMLxhPmVPzgztkcFYq64mZVeEWsFfljGLIf9-JLwnV4FMg2qdOsCaT0W_B8O5gbU-9SiNKN2sO0WE8C7l_w6E0cWfAdjnK-PZM1ETUsqhyphenhyphenPcKbY4ExnSmUPVS-a2A7xwH02TqQn2g-i/s400/female+karyogram.jpg

Homologous nature is based on length of chromosomes

Location of gene - gene loci
Same gene loci on homologous pair - same gene

-> 2 versions of each gene for one characteristic
-> Versions are called alleles

http://www.monteweston.com/Biology/Bio/joalleles.gif

3.1 Sexual and Asexual reproduction

Describe the differences between sexual and asexual reproduction

1. Sexes
- Exist in sexual reproduction - male/female
- None in asexual

2. Cells
- Sexual reproduction needs gametes
- Sperm - male
- Egg - female
- Asexual - no gametes

3. Cell division
- Sexual reproduction - Meiosis - ½ total adult number of chromosomes in gamete cells
- In humans the number of chromosomes in each cell is 46 - in gamete cells there are 23 per cell
- Asexual reproduction - Mitosis / Binary fission
- The number of chromosomes is constant (two cells are identical)

4. Fertilisation
- Sexual - egg cell and sperm cell fuse together
- Asexual - no fertilisation

5. Variation / Difference
- Sexual - broad + many differences
- Asexual - small variation (due to mutation), almost all identical (clone)

What are some examples of genetic mutation in asexually reproducing species?

4.9 Carbon Cycle

1. Photosynthesis

CO2 + H20 -(chlorophyll + light)-> C6H12O6 + O2

CO2 - Atmosphere 0.03%

Photosynthesis reduces atmospheric CO2

2. Feeding

Passage of carbon through different trophic levels

Producer -> Primary consumer -> Secondary consumer

Primary con. takes carbon molecules from producer etc..

Carbon is passed down through chain

3. Respiration

C6H12O6 + O2 -(enzymes in cell)-> Energy + CO2 + H2O

Adds CO2 to atmosphere

(All trophic levels/consumers/producers respire)

4. Decomposition

All organisms die

Organic molecules -(bacteria, fungi)-> CO2

Decomposition releases CO2

5. Combustion

a) Fossil fuels [oils, coals] -> CO2

(formed by compression and pressure of biomass)

industrial/cars, lorries etc

b) Occurrence in environment naturally

e.g. Lightning striking trees, causing forest fires etc

http://www.windows2universe.org/earth/climate/images/carboncycle_sm.jpg

4.11 Gas Pollution

Pollution of air by sulphur dioxide and carbon monoxide

1. Sulphur dioxide (SO2)
Added to atmosphere by combustion of fossil fuels
- Factories
- Vehicles (oils, petrols)
SO2 + H20 -> Sulphuric acid
Sulphur + Water vapour

Sulphuric acid = Acid rain
Affects plants and animals
Plants 'burned' by acid rain
- Top of conifers dead
- Causes Ca2+ and Mg2+ ions to be leached from system, causes yellowing of leaves (chlorosis)
Acid rains form streams, lakes
- reduces pH (acidic)
- release of aluminium ions
- thickening of mucus that lines the gills of fish
- O2 from H2O reduced
- fish suffocates

2. Carbon monoxide (CO)
Produced when fossil fuels (coal, gas) burned with insufficient oxygen
Combines with haemoglobin in red blood cells
Forms molecule called Carbaminohaemoglobin
Blocks haemoglobin from carrying O2
Reduces O2 circulation
Toxic -> fatal

4.7 Energy efficiency

(Kilojoules)

In the producer, only 10% of the energy is transferred to primary consumer, and so on

Causes of losses

Producer -> Primary consumer -> Secondary consumer

100 kJ -> 10 kJ -> 1 kJ

1) Respiration (energy lost by primary consumer)

2) Plant cell wall cannot be digested (not all of the plant can be digested) -> Faeces

-- 90 kJ loss --

3) Not all of primary consumer is available to secondary consumer

All eventually die

Broken down by decomposers