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  • Created by: Kelly
  • Created on: 05-05-13 16:08

Nature & Developtment

  • DNA sequence determines amino acid sequence. 
  • Proteins and enzymes are formed.
  • Enzymes enable metabolic pathways.
  • Metabolic Pathways help determine nature and developtment. 

The order of bases in the gene determines the order of amino acids.

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  • Genes are sections of DNA found on chromosomes that code for proteins.
  • They contain instructions for proteins to be made.
  • Proteins are made form amino acids.
  • Different proteins have a different number and order of amino acids.
  • Its the order of the nucleotide bases in a gene that determines the order of amino acids because 3 bases (triplet) codes for an amino acid.
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Gene Mutations can result in non funtioning proteins.

  • Mutations are changes in the base sequence of DNA.
  • Mutations can produce new alleles in genes.
  • A gene codes for a protein, so if the order of bases changes in a gene then a non functional protein could be produced.
  • All enzymes are proteins, if theres a mutation in a gne that codes for an enzyme it may fold up differently and have the wrong structure so in turn a different shaped active site so no substrate can bind.

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Crossing Over

Crossing over:

  • Homologous pairs of chromosomes come together, and the chromatids cross over. Swap alleles so they now have a different combination of alleles.
  • Each cell has a diferent chromatid with a different combination of alleles which increases genetic variation.

HAPLOID: Only one copy of each chromosome.

DIPLOID: TWO of each chromosome- one from mam, one from dad. (Normal body cells.

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Mitosis produces genetically identical cells. It occurs in the cell cycle.

NEEDS: Growth and Repairing damaged tissues.


Interpahse: DNA is unravelled and replicated as well as organelles. ATP content is increased.

Prophase: The chromosomes condense (shorter and fatter). Centrioles move to opposite ends of the cells forming the spindle. The nuclear envelope breaks down.

Metaphase: Chromosomes line up along the middle of the cell and become attatched the the spindle by their centromere.

Anaphase: Centromeres divide separating the sister chromatids. Spindles contract pulling chromatids to opposite ends of the cell centromere first.

Telophase: Chromatids uncoil and become thin again (chromosomes again). Nuclear envelope forms around each group of chromosomes and the cystoplasm divides.

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  • If theres a mutation in a gene that controls cell division the cells can grow out of control, forming a tumour.

Cancer Treatments:

Chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for DNA replication. So the cells cant enter the S phase forcing it to kill itself.

Radiation damages DNA. In the S phase it checks for damage and if detected, kills itself.

A chunk of tumour is often removed in surgery which increases the access of any left to nutrients ect so the cell enters the cell cycle where the cells are more susceptible to treatment.

Repeated Treatments are given with breaks to allow the body to recover (treatment kills normal cells too). It is repeated to kill any tumour cells not killed that carriend on dividing in the break.

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DNA Replication & The Cell Cycle

  • Hydrogen bond break by DNA helicase.
  • Both original strands act as templates.
  • Free complimentary nucleotides attach to exposed bases.
  • DNA polymerase joins nucleotides on NEW strands.

THE CELL CYCLE Consists of a period of cel growth, DNA replication (interphase) and a period of cell division (mitosis). Interphase- G1 S G2

G1 - Cell grows, new organelles and proteins made.         S - Cell replicates DNA

G2 - keeps growing           Mitosis

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DNA is a polynucleotide. Each nucleotide has a phosphate group, a deoxyribose sugar and a nitrogenous base. There are 4 possible bases : Adenine Thymine Cytosine and Guanine. DNA nucleotides join together to form polynucleotide strands, the nucleotides join up from the phosphate group of one and the deoxyribose sugar of another forming a sugar phosphate backbone. Two strands join together by hydrogen bonds forming between bases, by specific base pairing.

DNA's structure makes it good at its job. It contains all genetic information, DNA molecules are very long and coiled up tightly so is compact to store a lot of genetic information in a small space. It has a paired structure which make it easier to copy itself and the double helix structure means DNA is very stable. 

Contains linear DNA that exist as chromosomes. The DNA molecule is wound around histone proteins (which also help support the DNA). Then the DNA and the protein are coiled up very tightly to make a compact chromosome.
Also carry DNA as chromosomes but the DNA is shorter and circular and not associated with proteins. It condenses to fit in the cell by supercoiling. 

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Not all DNA codes for proteins. Sections of DNA that don't code for proteins are called introns. (Exons do). Introns are removed during protein synthesis. DNA also contains multiple repeats (DNA sequences that repeat over and over). They dont code for amino acids either.

Genes can exist in different forms called alleles. DNA is stored as chromosomes, humans have 23 pairs of chromosomes (46 all together). Pairs of matching chromosomes are called homologous pairs, they have the same genes but different alleles. Alleles on homologous pairs of chromosomes are found in the same position.

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Meiosis and Sex Cells

DNA from one generation is passed onto the next by gametes. Gametes are sex cells. Normal body cells have the diploid number of chromosomes (each cell has two of each chromosome). Gametes have a haploid number of chromosomes (only one copy of each chromosome). At fertilisation two haploid gametes fuse forming a zygote with the correct number of chromosomes (diploid).

INDEPENDENT SEGREGATION:This is when any allele of one gene can go with any allele of another gene. So gametes have a different combination of alleles increasing genetic variation. 

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