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67 Cards in this Set

  • Front
  • Back

DEFINE DNA

Deoxyribose nucleic acid


located in the nucleus


controls all the chemical changes in the cells


The kind of cell which is formed ( Muscle, blood, nerve) is controlled by the cell


The kind of organism produced is controlled by the cell


DOUBLE HELIX STRUCTURE

NUCLEOTIDE

Phosphate group
-PO4

Phosphate group


-PO4

RIBOSE VS DEOXTRIBOSE

Ribose is a sugar, like glucose, but with only five carbon atoms in its molecules


Deoxyribose is almost the same but lacks one oxygen atom

ORGANIC BASES

Adenine - Thymine/Uracil (2 H bonds)



Cytosine - Guanine (3 H bonds)



PURINES


Adenine Guanine


PYRIMIDINES
Thymine Cytosine


CHARGAFF'S RULE

-Adenine must pair with Thymine


-Guanine must pair with Cytosine


-Their amounts in a given DNA molecule will be about the same

DNA CHARACTERISTICS

STRONG bonds between deoxyribose sugar and phosphates


WEAK bond between hydrogen and organic bases


Weak bond easily breaks when heat is applied


WHEN DOES DNA SYNTHESIS OCCUR?
INTERPHASE, Meiosis

DNA REPLICATION

-The DNA begins to separate.


-Each strand makes a new partner by adding appropriate nucleotides.


-Result is there are now two double-stranded DNA molecules in the nucleus.


-So when the cell divides, each nucleus contains identical DNA


REPLICATION #1

-DNA polymerase comes onto the scene


-HELICASE: UNWINDS the DNA upstream and then UNZIPS the DNA.


- This site is known as the replication bubble.

REPLICATION #2

- Complementary bases begin adding into both sides of DNA


- A binds with T, C binds with G (no other possibility because of the shape of the base).

REPLICATION #3

- The final job of the polymerase is to PROOFREAD the nucleotides after they are added and clip out any that are incorrectly paired.

ENZYMES INVOLVED

HELICASE: unzips and unwinds DNA


PRIMASE: begins synthesis of new strands


POLYMERASE: joins new nucleotides to the strand


LIGASE: 'glues' new nucleotides together.

GENETIC CODE

The sequence of bases (A,T,G,C)

WHAT DOES A TRIPLET CODE FOR?

Amino Acids.


The different amino acids and the order in which they are joined up determines the sort of protein being produced.

WHAT DO AMINO ACIDS CODE FOR?

PROTEINS

AMINO ACIDS (list)

-Serine


-Cysteine


-Valine (C, A, T)


-Glycine


-Alanine (C, G, A)

WHAT DO PROTEINS MAKE?

-ENZYMES


-They also build the cell structure as well as hormones

WHAT MAKES UP A GENE?

A sequence of triplets in the DNA molecule that codes for a complete protein

PROTEIN SYNTHESIS

- Proteins are synthesised by joining amino acids together


- Sequence of amino acids that make up different proteins in known by the DNA


- Ribosomes in the cytoplasm are the organelles which put together the amino acids, they need sequence form DNA which cant leave nucleus.


- 2 distinct processes involved

TRANSCRIPTION

The part of the DNA molecule that the cell wants information from the make a protein unwinds to expose the bases


Free mRNA nucleotides in the nucleus base pair with one strand of unwound DNA molecule

TRANSCRIPTION

mRNA copy is made with the help of RNA polymerase. This enzyme joins up the mRNA nucleotides to make mRNA strand.


mRNA strand is a complementary copy of the DNA


mRNA molecule leaves the nucleus via a NUCLEAR PORE into the cytoplasm

TRANSLATION

mRNA travels to the ribosome


mRNA copy attaches to a small subunit of the ribosome in the cytoplasm or ER


Transfer RNA (tRNA) exists in the cytoplasm and attaches to amino acids


tRNA molecules 'collect' amino acids


CODON: group of 3 nitrogenous bases

TRANSLATION

tRNA bons with mRNA via its anticodon. It has an amino acid attached.


A second tRNA bonds with the next three bases of mRNA, amino acid joins onto the amino acid of first mRNA via a PEPTIDE BOND


Ribosome moves along. First tRNA leaves the ribosome. A third tRNA brings a third amino acid.


Stop condon reached. new polypeptide leaves

PLASMID

PLASMID: A circular piece of DNA that exists apart from the chromosome and replicates independently of it

PLASMID: A circular piece of DNA that exists apart from the chromosome and replicates independently of it

WHAT IS RECOMBINANT DNA?

-DNA that has been cut from one strand of DNA and then inserted into the gap of another piece of DNA that has been broken.


- Host DNA often bacteria


- Purpose is so the host can produce many copies


-Bacteria reproduces in very short time so it is possible to make millions of copies quickly.

HOW IS IT MADE?

-The required gene is cut from the DNA using a restriction enzyme.


-Plasmid is removed from bacteria and cut open using same restriction enzyme.


-The cut human gene is then mixed with the plasmid in a test tube.


-The cut ends of the plasmid and human gene match beause they were cut by the same enzyme, 'STICKY ENDS' - LIGASE sticks ends

RE-INTRODUCING PLASMID

-The plasmid needs to be reintroduced into bacteria so they can multiply the gene


-Can be don by combing in a test tube with CaCl2. The high concentration of calcium ions makes bacterial membranes more porous.


-Plasmids can now move back into the cells.


-Not all bacteria takes up plasmids so this is why monitoring must happen

ISOLATING HOST BACTERIA

-Only want the recombinant DNA


-By having a gene on the same plasmid the gives resistance to an antibiotic, the non hot bacteria can be removed by culturing bacteria in a medium of anitbiotic.


-The bacteria containing resistance will survive whilst the ones that are not needed will simply die.

POSSIBLE IN ALL CELLS?

-No, will not work in eukaryotic cells


-Other methods are used


- VIRAL VECTORS: virus injected into DNA of animal host.


-GENE GUN: used to insert genes into plant cell

EXAMPLES

1) Insulin for diabetics


2) Wheat crops that are attacked by insects


3) People sick with cystic fibrosis

POLYMERASE CHAIN REACTION

Enables large amounts of DNA to be produced from very small samples.


There is a repeating cycle of: SEPARATION of double DNA strands SYNTHESIS of a complementary strand for each

4 MAIN COMPONENTS OF PCR DNA

1) DNA Template


2) Primers


3) Polymerase


4) Buffer Solution

3 STEPS OF THERMAL CYCLING

1) Denature DNA


2) Primer Annealing


3) Extension

DENATURE DNA

-DNA heated to 95C


-Breaks weak hydrogen bonds that hold the DNA strands together


-Allowing strands to separate creating single stranded DNA

PRIMER ANNEALING

-Mixture cooled to 45-72C


-Allows the primers to bind(anneal) to their complementary sequence in the template DNA.

EXTENSION

-Reaction heated to 72C - optimal temperature for DNA polymerase to act


-DNA polymerase extends the primers


-Adding nucleotides onto the primer in a sequential manner


-Using target DNA as a template.

BENEFITS OF PCR

- Can create many copies from a minimal starting amount.


- Paternity Test


- Recombinant technology

GEL ELECTROPHORESIS

-Techniques used to separate DNA fragments by size.


-The gel (agarose) is subjected to an electric charge.


-The DNA (negative charge) migrates towards the positive pole.


-Larger DNA fragments move slower through the gel matrix


-DNA seen using fluorescent dyes

WHO WAS ADOPTED?

WHO WAS ADOPTED?

S2


Has alleles not present in either parent

GENOME

-An organisms entire genetic make up


-Includes all their chromosomes, genes, and DNA

HUMAN GENOME PROJECT

-Set out to identify all the genes in the human genome (about 25,000) and discover the sequence of base pairs (about 2.8 billion)


-99% of the gene-containing part of human DNA had been analysed by 2003.

MAPPING

Identification of genes and their positions in the chromosome.


Special staining methods reveal bands in the chromosomes.

SEQUENCING

Aims to fond out the sequence of nucleotides in a stretch of DNA


Automated to give results quickly


Analysis of small piece of DNA to give results like:


GCTTATCGATTCCGAT

DNA MICROARRAY

-Allows simultaneous measurement of the level of transcription for every gene in a genome


-Microarray detects mRNA

MANUFACTURE MICROARRAY

-Start with individual genes


-Amplify all of them using polymerase chain reaction


-"spot" them on a medium


-Spotting done by robot


-Complex and potentially expensive task

DEFINE MEIOSIS

-The form of cell division by which gametes, with half the number of chromosomes, are produced.


-Diploid(2n) - Hapliod(n)


-Two divisions (meiosis l and meiosis ll)

HOMOLOGOUS CHROMOSOMES

-Pair of chromosomes that are similar in shape and size.


Homologous pairs carry gene controlling the same inheritable traits.


-Each locus (position of gene) is in the same position on homologues.

INTERPHASE 

INTERPHASE

-Chromosomes replicate


-Each duplicated chromosome consists of two identicle sister chromatids attatched at their centromeres


-Centriole pair also replicate


-CROSSING OVER occurs

PROPHASE l

PROPHASE l

-Longest most complex phase (90%)


-Chromosomes condense


-SYNAPSIS: homologous chromosomes come together to form a TETRAD (two chromosomes or four chromatids)

METAPHASE l

METAPHASE l

-Shortest phase


-Tetrad align on equator


-Independent assortment occurs


1. Orientation of homologous pair to poles is random


2. Variation


3. Formula 2n

ANAPHASE l

ANAPHASE l

-Homologous chromosomes separate and move towards the poles.


-Sister chromatids remain attached at their centromeres.

TELOPHASE l

TELOPHASE l

-Each pole now has haploid set of chromosomes.


-CYTOKINESIS occurs and two haploid daughter cells are formed.

MEIOSIS ll

-No interphase (or very short - no more DNA replication)


-Meiosis ll is similar to mitosis

PROPHASE ll

PROPHASE ll

-Chromosomes condense


-Synapsis occurs, homologous chromosomes come together to form a tetrad.

METAPHASE ll

METAPHASE ll

-Tetrads align on the equator


-Independent assortment occurs:


1.Orientation of homologous pairs to poles is random.


2.Variation

ANAPHASE ll

ANAPHASE ll

-Homologous chromosomes separate and move towards poles.


-Sister chromosomes separate.

TELOPHASE ll

TELOPHASE ll

-Nuclei form


-Cytokinesis occurs


-Four haploid daughter cells produced


gametes - sperm or egg

CROSSING OVER

-The exchange of chromosomal segments between two non-sister chromatids


-Occurs at one or more points along adjacent homologoues during synapsis


-Points contact each other


-DNA is exchanged

CROSSING OVER BASICS

-Genes that are far apart have a greater chance of crossing over


-Genes that are closer have a less likely chance of crossing over


-Genes that stay together are LINKED

KINDS OF CROSSING OVER

1.Single crossing over - only one chiasma is formed. only one chromatid of each chromosome id involved.


2.Double crossing over - Two chiasma are formed. Formed between the same or different chromatids, so 2 or 3 chromatid may be involved


3.Multiple crossing over - More then one chiasma are formed

FACTORS AFFECTING CROSSING OVER

1.HIGH TEMPERATURE - increase frequency


2.X-RAY - increases frequency


3.AGE - decreases frequency

DISCONTINUOUS VARIATION

-Entirely genetically controlled


-cannot be altered by external conditions


-You either have the condition or you don't


-Example- colour blindness, dwarfisim, albanism, sickle cell anaemia

CONTINUOUS VARIATION

-The situation in which there are a great many intermediates between extremes


-Example- different shades of hair colour


-Variations under genetic control but there are several pairs of genes involved. (genome AA,Bb)

DEFINE MUTATION

A mutation is a spontaneous change in a gene or chromosome.

GENE MUTATION

-Result of faulty replication of DNA


-in a nucleotide is not copied right, the triplet will not code for the right amino acid


-protein will not function with wrong amino acid


-no protein = no enzyme


-no enzyme = no functioning orgamism

CHROMOSOME MUTATION

-Result of:


Damage to, or loss of chromosome


Incomplete separation of chromosomes


doubling a whole set of chromosomes


i.e. Down syndrome (47 not 46)


Klinefelters syndrome (XXY)