Biology
Class Notes
Lesson 21 The Structure and Role of RNA
Objective: 3.1.1, 3.1.2, 4.1.2
DNA Determines Protein Characteristics
 Information stored in DNA is used to make proteins
 Genetic traits are determined by proteins
 Proteins are chains of amino acids. Humans have 20 amino acids.
 The combination and arrangement of amino acids determines a protein’s shape and purpose.
Protein Synthesis
 Every cell contains a complete copy of the organism’s DNA.
 The creation of proteins defined by DNA occurs through the steps of transcription and translation.
 Only the proteins necessary for the functioning of a specific cell type (i.e. liver cells) are transcribed
within that cell.
 Proteins are assembled on ribosomes.
RNA (Ribonucleic acid)
• Single stranded
• Carries info from the DNA in the nucleus to the ribosomes.
• Uracil (U) replaces thymine, so in RNA it’s A + U, not T
• Contains ribose as a sugar
• Three main types of RNA: mRNA (messenger), tRNA (transport), rRNA (ribosomal)
Base Pairing Rules for RNA
 Cytosine bonds with Guanine
 Thymine bonds with Adenine
 Adenine bonds with Uracil (not Thymine as with DNA)
Ex:
Template:
A-T-T-C-C-G
Complement:
U-A-A-G-G-C
Steps of Protein Synthesis:
DNA
↓
Transcription (in nucleus)
↓
mRNA (transfers information)
↓
Translation (in cytoplasm)
↓
Protein
Codons: Arrangements of 3 nucleotides that code for amino acids.
Transcription
• DNA is used to communicate a code determined by the order of nucleotide bases.
• The process is similar to DNA replication with two exceptions: 1) transcription produces on one strand
of nucleotides and 2) uracil replaces thymine.
• Nucleotides are arranged in sets of three (triplets).
• 64 possible code words
Steps of Transcription
1. DNA splits
2. Complementary bases of RNA are added to the strand and a new strand of RNA is formed.
3. The DNA strands used as a template reconnect.
4. Messenger RNA (mRNA) carries the instructions from DNA to where they will be translated.
5. Instructions in mRNA are arranged in sequences of three nucleotides called codons.
6. Each codon codes for an amino acid, or the beginning/end of a protein.
Translation
1. The info is translated as information from mRNA into a sequence of amino acids using 3 base
anticodons on tRNA. The sequence of bases on tRNA is specific to the amino acid it carries.
2. Transfer RNA (tRNA) carries amino acids to the ribosomes where ribosomal RNA (rRNA) assists
with the process of joining them to form proteins.
3. Once the tRNA releases its amino acid, it is free to bond with another amino acid and continue the
process while other tRNA already carrying amino acids deliver them to the growing amino acid chain…
Gene Expression
Chromosomes: Compressed/tightly coiled bundles of DNA (double helix) that are wrapped around proteins
for organization.
• Are formed at the beginning of cell division.
• The # and arrangement for healthy individuals within a species is the same.
• The number of c’somes among species doesn’t correlate with complexity.
• They are only found in eukaryotes. In prokaryotes, the DNA stays in a ring and doesn’t compress.
Karyotype: All of the chromosomes for a given individual or organism.
• The human karyotype has 46 c’somes (23 pairs, including 2 sex c’somes).
• Human males have X and Y sex chromosome and females have X and X.
Organism
No. of
Chromosomes
Organism
No. of
Chromosomes
Cat
32
Peas
14
Chimp
48
Corn
20
Dog
78
Mosquito
6
Cow
60
Honeybee
32
Human
46
Sugarcane
80
Horse
64
Sand
Dollar
52
Human Karyotype Photo
Build a Karyotype Lab (http://learn.genetics.utah.edu/content/begin/traits/karyotype/)
Genes
Gene: A section of a c’some that codes for a single trait.
• There are many more traits than c’somes (46). Therefore, only a small part of each c’some codes
for a trait.
• They control the production of proteins.
Gene Expression/Regulation: A system that determines if a gene is turned on or off in a cell
 If the gene is off, the protein it codes for is not produced.
 In eukaryotes, genes are controlled individually.
 Not every gene is expressed in an organism.
– Ex: Genes for skin cells are not expressed in liver cells.
– Ex: Genes associated with tissue repair are not turned on until the tissue is damaged.
 Producing too little protein can cause problems as with aging and producing too much protein can
lead to cancer.
Create a “Karyotypes of Genetic Disorders” PowerPoint.
Include the following:
Normal Human Male karyotype
Normal Human Female karyotype
Cystic Fibrosis
Huntington Disease
Sickle Cell Disease
Edwards Syndrome
Turners Syndrome
Klinefelter Syndrome
Down Syndrome
For each genetic disorder above, provide: an image of the karyotype, image of an affected individual, rate
of occurrence, symptoms, and a brief statement about the cure/treatment.
Key Words:
RNA
Protein Synthesis
Transcription
Messenger RNA (mRNA)
Codon
Translation
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Gene Expression/Regulation