Where is the DNA located
- 3 places in eukaryotic cells
1) Within the nucleus ( DNA)
2) In mitochondrie ( mtDNA)
3) In chloroplasts ( chloroplastic DNA) - no 2 and 3 = extra-nuclear DNA
- Nuclear DNA = found tightly intertwined forming parts of the chromosomes
- Non-dividing cells chromosomes aren’t visible but are a mass of threads ( chromatin network)
What is the structure of DNA
- DNA = made up of nucleotides which are the building blocks of nucleic acids
- Nucleotide has 3 parts :
1) phosphate ion
2) deoxyribose sugar
3) nitrogen base - There are 4 nitrogen bases:
1) Adenine which pairs with thymine
2) Guanine which pairs with cytosine- Base pairs = held together by weak hydrogen bonds
- 2 between A & T
- 3 between G & C
- Base pairs = held together by weak hydrogen bonds
- Ladder like DNA twists so that one strand coils around the other to form a double helix which is further coiled around bead-like proteins called histones
What are the functions of DNA
- In the nucleus :
1) controls cell functioning
2) controls protein synthesis ( thus formation of hormones; proteins; enzymes)
3) stores hereditary info and transmits the info from one generation to the next - In chloroplasts and mitochondria it controls protein synthesis
Explain the storing of hereditary info
- Transmits characteristics like hair type; eye colour; tallness etc
- Are located in short segments of DNA called genes
- Gene = made up of at least 150 nucleotides in a specific sequence
Explain non-coding DNA
- Are components of an organisms DNA that don’t encode protein sequences.
- some = transcribed into functional non-coding RNA molecules ( eg. transfer RNA)
- ’’ Junk DNA’’ = non-coding DNA with no known biological functions but now there might be functions for it ( eg. acts as switches to determine when and where the gene gets expressed)
Explain DNA replication and its significance
- Occurs during interphase
- Involves making an identical copy of DNA
- Occurs in the nucleus before mitosis and meiosis and is controlled by enzymes
-Significance :
1) Ensure the daughter cells in mitosis will have identical genetic make ip as the parent cell
2) Before mitosis ensures that the chromosome no in each daughter cell is the same as the np in the parents cell
3) Ensures genetic properties are transmitted from one generation to the next
Explain the steps in DNA replication
1) DNA unwinds from one end to appear as a ladder
2) The weak hydrogen bonds between nitrogen bases break and the two single strands move apart
3) Each single strand picks up free nucleotides from the nucleoplasm and becomes double again
4) The two new double strands are identical to each other and to the original. Each double strand now becomes twisted and helical in structure
Explain DNA profiling
- Uses fingerprints from the crime scene and a match is made to identify the person who left behind the fingerprints
- A match = person is guilty of the crime
- Can done using body tissue; body fluids and hair with its root attached
- Each pattern obtained is unique except for identical twins, otherwise two people having the same DNA profile is very rare
- not always accepted in court as you can ‘‘plant’’ DNA at crime scenes to frame someone
How do you obtain a DNA profile
1) DNA sample is cut into fragments of varying lengths by restriction enzymes
2) DNA fragments are sorted into bands by gel electrophoresis
3) DNA fragments are transferred to a filter sheet and radioactive DNA probes are added
4) Radioactive DNA sows up as dark bands when placed on x-ray film
Advantages and disadvantages of DNA Fingerprinting
Advantages:
- Criminal cases : DNA profile is identical to the evidence found at a scene = person is guilty or was at scene
- Identifying individuals : siblings separated at birth; children separated from parents
- Making positive identifications of unrecognisable human remains ( eg. in wars)
- Paternity tests
- Diagnosis of inherited genetic disorders in unborn / newborn babies
Disadvantages:
- Expensive process
- The process = subject to human error
- Can be used to frame innocent people
- Not everyones DNA has been profiled
- Profiling innocent peoples DNA may infringe on individual rights
Explain RNA
- Single stranded and shorter than DNA
- Made up of nucleotides each consisting of a phosphate ion; ribose sugar and nitrogen base
- 4 Nitrogen bases: Adenine; uracil; guanine; cytosine
- 3 types of RNA:
1) Ribosomal RNA ( rRNA)
- Combine proteins to form ribosomes
2) Messanger RNA ( mRNA )- Formed in nucleus and move into the cytosol; plays a role in protein synthesis
3) Transfer RNA (tRNA) - found in cytosol and plays a role in protein synthesis
- Formed in nucleus and move into the cytosol; plays a role in protein synthesis
Difference between DNA and RNA
DNA:
-Double stranded
-Pentose sugar is deoxyribose
- Bases are paired
- Chains are very long
- Helical shape
- Nitrogen bases : A;T;G;C
RNA:
-Single stranded
Pentose sugar is ribose
- Chains are relatively shorter
- No pairing of bases occurs
- Nitrogen bases : A;U;G;C
- Various shapes
What is protein synthesis
- A process whereby proteins are manufactured in a cell
-Proteins ( hormones; enzymes) = made up of amino acids - A protein type is determined by the number and sequence of the amino acids in the chain
Explain how DNA controls the synthesis of proteins
1) Transcription:
- A process whereby a mRNA is built on a DNA template
2) Translation
- A process whereby different amino acids are assembled to forma specific protein
Explain transcription fully
- In cell nucleus
- DNA unwinds and splits into 2 where H bonds break
- One DNA strand = template to form mRNA
- Free RNA nucleotides from nucleoplasm = attach to DNA template
- to form mRNA
-mRNA = now has the coded message for PS
-mRNA breaks away from the DNA and moves into cytosol via a nuclear pore
- and becomes attached to a ribosome
Explain translation fully
- Each tRNA carries a specific amino acid
- When the anticodon on tRNA matches the codon on the mRNA, tRNA brings along its amino acid
- Amino acids become attached by peptide bonds
- To form a particular protein
Explain the DNA extraction practices fully
1) Chop onions
- To seperate and break d cell walls
2) Add a solution of salt and soap
- Salt: causes DNA to precipitate in the alcohol
- Soap : causes the cell membrane and nuclear membrane to break d so the DNA is released from cells
3) Heat in a water bath
- Softens phospholipids in cell membranes and denatures enzymes that would otherwise cut DNA into smaller pieces
4) Cool in a cold bath
- Slows down rate at which DNA breaks up
5) Filter Mixture
- To filter out large particles and the DNA from the solution
6) Add alcohol
- Dissolves soluble components ( not the DNA). DNA and salt precipitate clump together out of the solution
7) Spool the DNA onto a glass rod
What are mutations and the types
- An unpredictable change in the DNA of an organism
- they occur when mistakes are made in the process of DNA replication
Types:
- Chromosomal
-Gene
Explain chromosomal mutations fully
- Some mutations involve larger sections of chromosomes
- involve a change in the number or structure of whole chromosomes
- Only happen during meiosis
- Abnormal gametes and offspring are produced
eg. Down syndrome
Explain gene mutations fully
- Small, permanent change in the structure of a gene and as a result of a change in the DNA nucleotide sequence
-Happens in DNA replication or RNA transcription
- Affect sequences of bases in a DNA molecule and thus the sequence of amino acids on the protein that ti=his piece of DNA is coding for
- Causes a change in the info that the gene gives to the cell which will either cause faulty or abnormal protein
eg. Albinism or sickle cell anaemia
Explain point mutations types fully
1) Those that affect many codons
- Caused by insertions or deletions of bases in DNA
- Changes the reading foramen the DNA
Results in a Frameshift mutation
2) Only affect one codon
- Caused by inversion or sub of bases in DNAE
Explain DNA profiling in paternity testing
- DNA profile of mother and father and child must be taken
- Profile of mother and child must be compared
- Half DNA bands of mother and child will match
-Profile of father and child must be compared - The remaining bands of the child must match with those of the father
- If the remaining bands match the father then he is the father
- If they don’t match with the father then he is not the father
