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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