Central Dogma
First step: a genetic message from DNA is to copied (transcribed) into mRNA, which contains the code for making proteins
Second step: is to decode mRNA into a polypeptide chain which builds a protein.
Functions of a Protein
Functions of Protein:Functions of Protein:
• StructuralStructural– muscle, hairmuscle, hair
• ChemicalChemical– antibodies, hormones, enzymes (regulate antibodies, hormones, enzymes (regulate
all chemical reactions in cells)all chemical reactions in cells)
Proteins
• Proteins are made, from mRNA, by joining amino acids into long polypeptides (which are proteins)– There are only 20 naturally occurring amino
acids
Review of DNA
• DNA is the genetic material
• DNA codes for different genes– Genes are codes for a protein which
determines different traits
DNA is made up of nucleotidesWhich contain: - a phosphate group
- a sugar (deoxyribose)- a nitrogenous base
RNA
• Involved in protein synthesis• Made up of nucleotides:
–Nitrogenous bases (RNA only has A, U, C, G there is no T!)
–A phosphate group
–A sugar (ribose)
Types of RNA
• There are three main types:–Messenger RNA (mRNA)–Transfer RNA (tRNA)–Ribosomal RNA (rRNA)
mRNA
• Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.
Transcription• Flow of info: DNA -> mRNA
• Location: Nucleus
• mRNA is produced by copying part of the DNA
– The mRNA leaves the nucleus and goes into the cytoplasm and attaches to the ribosome.
Transcription
• Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.
The Genetic Code
• The genetic code is read from mRNA– mRNA made off of a strand of DNA is read.
• mRNA is only 4 letters A, U, C, and G
• The code is read 3 letters/bases at a time• Codon= three consecutive nucleotides
which are specific for an amino acid
Translation
• Flow of info: mRNA -> Proteins
• Location: Cytoplasm/Ribosomes
• Translation is decoding mRNA into a polypeptide chain(protein)
Step 1 Translation
• mRNA attaches to a ribosome
• The start codon (AUG) is located by tRNA
• The matching tRNA, containing the anitcodon UAC, will bind to AUG
• The tRNA carries the animo acid specific to the mRNA sequence AUG, which is methionine.
Step 3As each new tRNA enters the ribosome, one leaves. Before tRNA can leave the ribosome, the animo acidswill bond together to make a polypeptide chain
Mutations• Changes in genetic material
• Many have little effect on gene expression or protein function
• A few can be harmful and then some are good– Harmful mutations can cause cancer and
genetic disorders– Good mutation can make altered proteins
which may be beneficial in different/changing environments
Point Mutations
• Mutation of 1 or more nucleotides– Substitution – changing one base, usually
only changes one amino acid– Insertion – addition of 1 or more bases,
causes frameshifts– Deletion – removal of 1 or more bases,
causes frameshifts
Chromosomal Mutations
• Change in number or structure of a chromosome– Deletion – loss of all or part of a chromosome– Duplication – extra copies of parts of
chromosomes– Inversion – reverse direction of parts of
chromosomes– Translocation – chromosome breaks and
attaches to another
Changes to Chromosome Number
• Monosomy 2n-1– 45 chromosomes– Turners (XO)
• Trisomy 2n+1– 47 chromosomes– Down syndrome(trisomy 21), Klinefelters
(XXY), Triple X (XXX), Jacobs (XYY)
• Polyploidy (Triploid, Tetraploid, etc)
Down Syndrome
•Mothers in early 20s 1 in 1,500 births•Mothers over 35 1 in 70 births•Mothers over 45 1 in 25 births