Download Genetics Exam Review #2

Genetics Exam Review #2
DNA & Protein Synthesis
DNA
• Structure of DNA was discovered in the 1950’s
by James Watson and Francis Crick in England.
• They were able to determine the structure of
DNA as a double helix by stealing a
photograph of work done by Rosalind
Franklin.
DNA
• DNA is made up of subunits called nucleotides.
• A nucleotide is made up of three parts: sugar,
phosphate and nitrogen base.
• The sugar in DNA is called deoxyribose.
• The four nitrogen bases in DNA are: adenine,
cytosine, guanine and thymine.
• DNA has base pairing rules: Adenine always pairs
with Thymine and Guanine always pairs with
Cytosine.
DNA
• What is the complementary DNA strand?
T-A-C-A-G-T-C-T-A-G-G-C-A-T-C-C-A-G-C-A-T
A-T-G-T-C-A-G-A-T-C-C-G-T-A-G-G-T-C-G-T-A
DNA Replication
• DNA replication is the process by which DNA makes an
exact copy of itself prior to cell division.
1. DNA double helix unwinds.
2. DNA strand is unzipped between the nitrogen bases. The
point at which it is unzipping is called the replication
fork.
3. DNA Polymerase adds nucleotides to each side of the
original DNA strand.
4. When DNA Polymerase reaches the ends of the strands,
two identical copies of the DNA have been made.
5. Each new strands winds back up into the double helix
structure.
RNA
• There are three main differences between
DNA and RNA:
1. RNA has the sugar ribose / DNA has the sugar
Deoxyribose.
2. RNA is single stranded / DNA is double stranded.
3. In RNA, adenine pairs with uracil / in DNA,
adenine pairs with thymine.
RNA
• There are three types of RNA:
1. Messenger RNA (mRNA) – carries message from
DNA in the nucleus to the ribosome for protein
synthesis.
2. Transfer RNA (tRNA) – brings amino acids to the
ribosome for protein synthesis.
3. Ribosomal RNA (rRNA) – makes up the structure
of the ribosome.
Transcription
• Protein synthesis is broken down into two
processes: transcription and translation.
• Transcription occurs in the nucleus. It is the
process of making mRNA from DNA.
• Transcribe the following DNA segment:
T-A-C-A-G-T-C-T-A-G-G-C-A-T-C-C-A-G-C-A-T
A-U-G-U-C-A-G-A-U-C-C-G-U-A-G-G-U-C-G-U-A
Translation
• Translation occurs in the cytoplasm at the
ribosome. It is the process of making a
protein from the mRNA.
• The ribosome reads the mRNA 3 nucleotides
at a time (a codon).
• A tRNA molecule brings the correct amino
acid to the ribosome based on its anti-codon.
• The ribosome continues adding amino acids
until it reaches a “stop” codon.
• It then releases the protein and begins again.
Translation
• Break the mRNA segment from above into
codons:
A-U-G U-C-A G-A-U C-C-G U-A-G G-U-C G-U-A
• What is the amino acid sequence for the
protein?
Met – Ser – Asp – Pro – Stop – Val – Val
• This diagram shows the process of
translation which occurs in the
cytoplasm.
• Molecule 1 represents mRNA,
which is made in the nucleus
during transcription.
• Molecule 2 is a ribosome (tRNA).
• Molecule 3 is an amino acid,
which are bonded together to
make proteins (Molecule 4).
• Molecule 5 is tRNA, which
contains the anti-codons and
brings amino acids to the
ribosomes.
Translation
Mutations
• A mutation is any change in a DNA sequence. These
changes can result in the wrong sequence of amino
acids in a protein – which will cause the protein to
function incorrectly.
1.
2.
3.
4.
Insertion – an extra nucleotide is added to the sequence.
Deletion – a nucleotide is removed from the sequence.
Inversion – a sequence of nucleotides is switched.
Duplication – a nucleotide or sequence of nucleotides is
repeated.
5. Substitution – a nucleotide is replaced with a different
nucleotide.