the genetic code biol 2401
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The Genetic CodeBIOL 2401Central Texas CollegeChelsea Barker, MS
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Cell Reproduction
•Necessary for continuation of life•Somatic cells divide to form two identical
daughter cells with complete genetic codes through mitosis
•Gamete cells divide to carry half of the genetic code (sperm and eggs) through meiosis
•Cells grow and go through other living processes until division occurs again (cell cycle)
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Cell Cycle
•Continual process of growth and division characterized in these steps▫Interphase▫Mitosis
Prophase Metaphase Anaphase Telophase
See Figure 3.35 in book.
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Interphase
•Cell undergoes growth•Carries out its specified functions•Synthesis phase: DNA replicates•Growth phase: other structures are
synthesized
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Mitosis•Prophase
▫ Chromatin condenses into identical chromatids•Metaphase
▫ Chromosomes align at the center along spindle fibers
•Anaphase▫ Chromosomes separate and move to opposite
ends of the cell along shortening spindle fibers•Telophase
▫ Chromosomes are at each end and begin to uncoil•Citokinesis
▫ Begins in anaphase where cell membrane begins to pinch off and continues through telophase
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Cell Cycle
See Figure 3.36 in book.
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Genetic Information
•Your genetic information contains instructions for cellular makeup through protein construction
•Gene-a sequence of DNA that codes for a particular protein
•Genome-entire set of genetic information
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Human Genome
See figure 24.3 in the book.
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Base Pairing• DNA
▫ Guanine-cytosine▫ Adenine-thymine
• Purines: A & G▫ 2 rings
• Pyridimines: T &C▫ 1 ring
• RNA▫ Guanine-cytosine▫ Uracil-adenine
*DNA is universal among species as a result of this base pairing.
*Triplicates code for the same amino acid in all species.
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DNA Structure•Base pairs are aligned in a particular
sequence•Hydrogen bonds hold base pairs together
and phosphate bonds hold adjacent nucleotides
•A “ladder” is formed and then twisted into a double helix
•Double helix DNA--->chromatin---> chromatid--->chromosome
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DNA Structure
See Figure 4.19 in book.
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DNA Replication•DNA must have an exact copy made so
that each daughter cell has a full genetic code
•Hydrogen bonds broken between base pairs
•Free nucleotides link up with the opposing nucleotide making new hydrogen bonds using the enzyme DNA polymerase
•DNA unwinds continuously to give two new double helix strands
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DNA Replication
See Figure 4.20 in book.
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RNA Molecules•Messenger RNA (mRNA)
▫ Formed through transcription (DNA to mRNA)▫ Each triplicate, called a codon, “codes” for an
amino acid▫ mRNA takes the information outside the nucleus
•Transfer RNA (tRNA)▫ Made of anticodons that match mRNA codons
with amino acids attached▫ Transfers amino acids to mRNA and translates
the codons of mRNA to specific amino acids to form proteins, a process known as translation
•Ribosomal RNA (rRNA)▫ Provides enzymatic activity for ribosomes
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Codons
See Table 4.2 in book.
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Protein Synthesis
See Figure 4.23 in book.
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Protein Synthesis
See Figure 4.24 & table 4.3 in book.
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DNA Mutation
• Bases get exchanged in replication of DNA or translation of RNA
• Some mutations are unnoticed
• Some mutations are large and change cellular function/metabolism
• Repair enzymes try to catch and correct mutations
• Example: cancer
See Figure 4.25 in book.
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Inheritance of DNA
•Gametes (sperm and egg) receive only half of the full genetic code during the division
•A full genetic code is restored when egg and sperm meet
•The paring up and unique set is obtained based on what “half” of each parent’s genetic code is passed on
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Punnett Square
XX XX
XY XY
X X
X
Y
MOM
DAD
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Genotype vs. Phenotype• The genetic make up of
the individual for a specific trait
• Expressed by letters▫ BB-2 dominant genes▫ Bb- 1 dominant, 1
recessive gene▫ bb-2 recessive genes
• The expression of the genetic make up of a trait in an individual
• Expressed by letters▫ BB-Brown eyes▫ Bb-Brown eyes▫ bb-Blue eyes
•Homozygous: sameDominant: BBRecessive: bb
•Heterozygous: different (Bb)
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Punnett Square Practice•Male or female child?
▫X-female, Y-male▫XX (mom) with XY (dad)
•Widows Peak?▫P-widows peak (dominant), p-straight
(recessive)▫Mom-widows peak (Pp) and Dad-straight (pp)
•Flower color in plants?▫C-red, c-white & can co-express to give pink
(Cc)▫Red flower (CC) and a white flower (cc)
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