Genetic Flashcards
Eukaryotic DNA
Long linear chromosones
DNA in nucleus
DNA tightly wrapped around proteins called histones
Prokaryotic DNA
Supercoiled - condenses circular chromosones so they can fit inside the cell
Short and circular
Bases of DNA
Adenine
Guanine
Cytosine
Thymine
Locus
Specific physical location of a gene or other DNA sequence on a chromosone
Exons
Coding regions in a gene
Introns
Non coding regions in a gene
Removed during splicing
Features of the genetic code
Degenerate
Universal
Non - overlapping
Degenerate
More than one codon can code for the same amino acid
64 possible triplet codes but 20 amino acids
Universal
Same four bases (A,T,C,G) are used in the DNA of every organism
Codons in DNA are transcribed into mRNA and translated into amino acids in every organism
Non - Overlapping
No overlapping between triplet codes
Each triplet is separate from other triplets
Substitution mutation
One base is substituted for another
eg. ATCCGT - ACCCGT
Name the 3 types of substitution mutation
Silent
Misense
Nonsense
Silet mutation
Base changes but doesn’t change the amino acid
eg. UCU = Serine , UCC = Serine
Misense mutation
Base changes and it changes the amino acid (alters binding site)
eg. AAG = Lysine , AGG = Arginine
Nonsense mutation
Base changes and alters amino acid to have a stop codon (anticodon) that is complementary
eg. UCU = Cystine , UGA = Stop
Stops DNA replicating
Name the two types of frameshift mutation
Deletion
Insertion
Deletion
One base is deleted
Causes codons to change which results in different amino acids
Changes the primary structure of a protein which results in a potentially whole different protein / faulty - leads to disease
Insertion
A base is added
Changes the amino acid sequence
How do mutagenic agents work
Increase the frequency of a mutation occurring
Act as a base
Alter a base
Change structure of DNA
Name the 3 mutagenic agents
Xray
Ionising radiation
Chemicals
What are the effects of mutation
Production of new/superior protein - results = gain of reproductive advantage
Neutral mutation - results = no change
Production of an inferior / no protein - result = fatal/ disease killing
Causes of mutation
A mutation can occur by mistake during DNA replication - spontaneously occur
DNA polymerase makes a mistake about once every 100,000,000
Transcription
Occurs in the nucleus
Transcription - Initiation
RNA polymerase attaches to the beginning of the DNA code - Promoter
The DNA molecule unwind and the weak hydrogen bonds between the complementary strands break
One strand now acts as a template for the formation of the mRNA strand
Transcription - Elongation
Free nucleotides in the nucleus bond to the complementary baes of the DNA template (Uraci replaces Thymine in mRNA)
More free nucleotides bond to their complementary bases , to elongate the mRNA strand , until the entire code has been transcribed
The RNA polymerase joins the nucleotides in condensation reactions (forms phosphodiester bonds)
Transcription - Termination
The mRNA will detach from the DNA template
The RNA polymerase detaches and starts all over again at a different location where needed
Now the pre-mRNA strand has to undergo modification and RNA splicing before it can leave the nucleus
Splicing
RNA splicing removes introns (non coding RNA) and joins exons (coding RNA)
Creates a mRNA molecule with continuous coding sequence
RNA
Ribonucleic acid
Single stranded
Consists of - pentose sugar (ribose) , phosphate group, base (A,U,C,G)
mRNA
Transfers the DNA code from nucleus to cytoplasm
Complementary to DNA code
Small enough to leave nucleus pore
Single stranded
tRNA
Small
Single stranded - folded into a clover leaf shape
Amino acid at top , Anti codon at bottom
Translation
A cell translates mRNA message into polypeptide
Translation - Initiation
Small ribosomal subunit binds with mRNA
Small subunit moves along mRNA until it reach the start codon (AUG)
The matching anti codon of the tRNA (with amino acid) bonds with start codon
Large ribosomal subunit is added - complete translation initiation complex
Translation - Elongation
More tRNA anticodon attach to mRNA codons
The amino acids attached to the tRNA’ attach to one another by peptide bonds
Amino acid form a long polypeptide chain
tRNA releases Amino acids to pick up more amino acids
Translation - Termination
Occurs when a stop codon in the mRNA reaches the active site of a ribosome
Releases polypeptide
Meiosis
Only takes place in sex organs - produces gametes
Starts with a diploid cell - results in 4 identical haploid cells
Contain individual chromosomes - not pairs
Homologus chromosones
One from mother and one from father
Both chromosones in a homologous pair have the same genes
Can inherit different alleles from each parent
Meiosis 1
Homologous chromosomes are separated from each other
Meiosis 2
Sister chromatids separated from each other
Meiosis - Interphase
Before meiosis the cell will have been through interphase
During interphase - cell copies chromsones and organelles
Chromosones not visible as distinct structures in interphase
Prophase 1
Chromosones condense and become visible
Homologous chromosones link together forming chiasmata
Crossing over takes place - exchanging alleles between homologous chromosones
Nuclear membrane breaks down
Metaphase 1
Homologous pairs of chromosones now line up along the equator
Anaphase 1
Spindle fibres shorten and homologous chromosones move to opposite poles
Chiasmata between homologous chromosones breaks
Telophase 1
Chromosones now reached poles of cell
Nuclear membrane reforms and chromosones move to opposite poles
Cytokinesis 1
Divides into 2 cells
Haploid
Cytokinesis 1
Divides into 2 cells
Haploid
Prophase 2
Chromosones condense and become visible again
Nuclear membrane breaks down and spindle fibres begin to develop
Metaphase 2
Chromosones are lined up on the equator
Anaphase 2
Centromere of each chromosome divides
Spindle fibres shorten
Chromatids pulled apart to opposite poles of cell
Telophase 2
Chromatids have reached the poles of the cell
Chromosomes
Nuclear membrane reforms and chromosones coil back to chromatid state
Cytokinesis 2
Produces 2 haploid cells
