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Biology I
D N A
• DNADNA contains genes, sequences of nucleotide bases
•These GenesGenes code for polypeptides (proteins)
• ProteinsProteins are used to build cells and do much of the work inside cells
DNA Begins the DNA Begins the ProcessProcess
• DNA is found inside the nucleus
• Proteins, however, are made in the cytosol of cells by organelles called ribosomes
• Ribosomes may be free in the cytosol or attached to the surface of rough ER
Starting with DNAStarting with DNA• DNA ‘s code must be copied DNA ‘s code must be copied
and taken to the cytosoland taken to the cytosol• In the cytosol, this code In the cytosol, this code
must be read so amino acids must be read so amino acids can be assembled to make can be assembled to make polypeptides (proteins)polypeptides (proteins)
• This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS
RNA~ Ribonucleic acidRNA like DNA consists of nitrogen bases, sugar-phosphate polymers, but there are also some differences.There are 4 main differences b/t RNA & DNA:
The sugar in RNA is ribose, DNA has deoxyribose
RNA is single stranded, DNA is double stranded
RNA contains the base uracil, DNA has thymine
RNA is smaller in size compared to DNA
Comparison of Structures DNA & RNA
Structure of RNAStructure of RNA
Since the base Thymine is being replaced by the base Uracil let’s answer the
following:
For the following DNA sequence add the complementary RNA nucleotides:
T T A G G C T G G A T G C T A A C
The complementary RNA sequence would be:
A A U C C G A C C U A C G A U U G
Question:Question:
What would be the What would be the complementary RNA complementary RNA
strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’
Answer:Answer:
•DNA 5’-GCGTATG-DNA 5’-GCGTATG-3’3’
•RNA 3’-CGCAUAC-RNA 3’-CGCAUAC-5’5’
Another difference between DNA & RNA is in the function. DNA has only one function~ STORING
GENETIC INFORMATION in it’s bases. But there are 3 main types of ribonucleic acid; each has a specific job
to do
1. Ribosomal RNA (rRNA) ~ exists outside the nucleus in the cytoplasm of cells in structures called ribosomes. Ribosomes are small, granular structures where protein synthesis takes place.
2. Messenger RNA (mRNA) ~ “records" information from DNA in the cells nucleus and carry it to the ribosomes. They serve as messengers to the cell.
3. Transfer RNA (tRNA)~ the function of transfer RNA is to deliver amino acids one by one to protein chains growing at ribosomes.
Messenger RNA
Ribosomal RNA
Transfer RNA
• The following diagram is an example for gene expression how the information in DNA is translated into organism’s traits
• RNA molecules are copied by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA
• This process by which DNA is copied to RNA is called Transcription, it requires the enzyme RNA polymerase & occurs in the nucleus of cells
Step 1~ Transcription begins when RNA polymerase binds to the “promoter” site (a specific sequence of DNA that acts as a “START” signal)
Step 2~ RNA polymerase unwinds & separates the two strands of DNA
Step 3~ RNA polymerase adds & links complementary RNA nucleotides
Transcription continues until RNA polymerase reaches the “STOP” signal on DNA
mRNA Transcript
•mRNA leaves the nucleus through its pores and goes to the ribosomes
• Proteins are made by the joining of amino acids into long polypeptide chains, which contain any combination of the 20 AA.
• The language of mRNA is called the genetic code.
• A sequence of 3 nucleotides in mRNA codes for each AA, are called codons.
• Codons consists of 3 bases that specify an AA, therefore the genetic code is read 3 letters at a time.
Let’s practice below:• Using the following DNA sequence:
ATCGTAACCGTTCTG
• Transcribe the DNA sequence into an mRNA sequence:
UAGCAUUGGCAAGAC
• Now break the mRNA sequence down where it can be read:
UAG CAU UGG CAA GAC
• Now identify the Amino Acids:Stop Hist Tryp Glut Asp
Use the code by reading from the center to the outside
Example: AUG codes for Methionine
Messenger RNA (mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
protein
A U G G G C U C C A U C G G C G C A U A AmRNA
startcodon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
Transcription
• Proteins are made by joining amino acids into long chains called polypeptides. The production of these proteins is called protein synthesis.
• Each polypeptide contains any of ____ Amino Acids
• The language of mRNA instructions is called the _____
• Codons contain___ nucleotides that specify a single AA
• Some AA are represented by more than one codon
• EX: __ codons specify AA Leucine, what are they?
• One codon AUG can represent Methionine or “START” codon for protein synthesis.
Stop codons are like periods at the end of sentence!!
Name the codons for the following AA:
• Tyrosine• Alanine• Glutamine
Name the AA for the following codons:
• AAA• CUG• UAG
THE MAKING OF PROTEINS
TRANSLATION• The decoding of an mRNA message into a
polypeptide chain (protein) is called translation, which takes place on ribosomes
• Amino Acids are transported by ribosomes & tRNA molecules, which have specific regions that bond to AA
• The loop attachment has a sequence of 3 nucleotides called anticodons.
• The tRNA anticodon is complementary & pairs with the mRNA codons.
• During translation or protein synthesis the cells use info from mRNA to produce the proteins
EX: The tRNA anticodon UAC would bind with the mRNA codon_______
• mRNA is transcribed from the DNA in the nucleus
• Translation begins when mRNA attaches to a ribosome at the start codon
• The pairing of codons & anticodons causes AA to attach to the growing polypeptide chain
• Each AA is added to the chain until it reaches a stop codon ending translation
A U G
Another Example of Translation
What is a Mutation? A mutation is a permanent change in the DNA sequence of a gene. Mutations in a gene's DNA sequence can alter the amino acid sequence of
the protein encoded by the gene.There are two main types of mutations:
Gene & Chromosomal
Gene mutations results from changes in a single gene there are two types:
Point & Frameshift Mutations
Point mutations~ these affect one nucleotide, because they occur at a single point in the DNA sequence & substitutes one nucleotide for another.
. ExampleDNA: TAC GCA TGG AATmRNA: AUG CGU ACC UUAAA: MetArg Thr Leu
Substitution DNA: TAC GTA TGG AATmRNA: AUG CAU ACC UUAAA: Met Hist Thr Leu
Frame shift mutations~ these include inserting a extra nucleotide or deleting a nucleotide, which shifts the “reading
frame” of the genetic message
DNA: TAC GCA TGG AATmRNA: AUG CGU ACC UUAAA: Met Arg Thr Leu InsertionDNA: TAT CGC ATG GAA TmRNA: AUA GCG UAC CUU AAA: Ile Ala Tyr Leu
Normal hemoglobin (eight out of the 146 amino acid units of normal hemoglobin)
Val His Leu Thr Pro Glu Glu Lys
Sickle-cell hemoglobin (the same section as above as found in Sickle-cell hemoglobin)
Val His Leu Thr Pro Val Glu Lys
Good red blood cells
Sickle cell blood cells
pictures from:www.cc.nih.gov/ccc/ ccnews/nov99/The function of normal human red blood cells, which are disk-
shaped, is to transport oxygen from the lungs to the other organs of the body. Each red blood cell contains millions of molecules of hemoglobin that carries the oxygen.
A slight change in the order of the amino acids in the hemoglobin molecule (valine substituted for glutamine), which has only 146 amino acids, causes sickle-cell disease. Abnormal hemoglobin molecules stick together and crystallize deforming the red blood cells. The deformed blood cells then clog tiny blood vessels impeding the flow of blood. Sickle-cell anemia kills about 100,000 people per year in the US
The molecular basis of sickle-cell disease
Environmental factors including radiation, chemicals, and viruses, can cause chromosomes to break; if the
broken ends do not rejoin in the same pattern, this causes a change in
chromosomal structure.
Types of Chromosomal MutationsInversion: a segment that has become separated
from the chromosome is reinserted at the same place but in reverse; the position and sequence of genes are altered.
Translocation: a chromosomal segment is removed from one chromosome and inserted on another chromosome
Deletion is a type of mutation in which an end of a chromosome breaks off or when two simultaneous breaks lead to the loss of a segment. a. Even if only one member of pair of chromosomes is affected, a deletion can cause abnormalities. b. Cri du chat syndrome is deletion in which an individual has a small head, is mentally retarded, has facial abnormalities, and abnormal glottis and larynx resulting in a cry resembling that of a cat.
Duplication is a doubling of a chromosomal segment. a. A broken segment from one chromosome can simply attach to its homologue. b. Unequal crossing-over may occur.
Examples of Mutations
DELETION
DUPLICATION
INVERSION
TRANSLOCATION
