Chapter 7 & 8 Flashcards
What are nucleotides made up of?
- one phosphate group
- 5 carbon sugar (pentose sugar)
- A nitrogenous base
How do the sub units of a nucleotide join together?
By a condensation reaction
How many nucleotides are needed to make up the whole genetic code?
4
What’s the difference between DNA and RNA? (structural)
Deoxyribonucleic acid - one less O2 on the 5-carbon sugar
Ribonucleic acid - one extra O2 on the 5-carbon sugar
DNA is double stranded and long, RNA is single stranded and much shorter
What are the nitrogenous bases of DNA?
Adenine, Cytosine, Guanine, Thymine
What are the nitrogenous bases of RNA?
Adenine, Cytosine, Guanine, Uracil
Which bases are purine and which bases are pyrimidines?
Purine:
Adenine & Guanine
Pyrimidines:
Thymine, Uracil, & Cytosine
What are the bonds between the bases?
A=T (double H bonds)
U=A (double H bonds)
C≡G (triple H bonds)
How are nucleotides joined together?
By a condensation reaction between the 5-carbon sugar and the phosphate group. The double strand is then formed by complementary base pairing.
What is complementary base pairing?
When A will only join to T and G will only join to C because of their specific structure
What is anti-parallel?
When one strand runs in one direction and the second strand runs in the other direction
How does DNA replication occur?
1- Helix unwinds
2- Backbone is unzipped by breaking H-bonds between bases (DNA helicase)
3- Free nucleotides are matched to their complementary base on their backbones
4- Condensation reactions join the nucleic acids in the new backbones (DNA polymerase)
5- The double strand twists again
Where is the phosphodiester bond found?
Between one mononucleotide and the phosphtae group of another
How is semi-conservative replication performed?
- Use bacteria like e-coli because they divide rapidly and are easy to culture (grow)
1- Grow the e-coli with heavy nitrogen (N15). The DNA would use this nitrogen in its structure
2- The e-coli are then transferred into a medium on=f light nitrogen (N14) just long enough for one round of DNA
3- The DNA is extracted and centrifuged
4- The DNA will lie in the part of the extract that has the same density as theirs
Where does protein synthesis occur?
In the ribosomes
What is a gene?
A gene is a length of DNA made up of a number of nucleotides tat codes for one specific polypeptide
Where are most genes found?
Most of the 25,000 human genes are found on the chromosomes in the nucleus but there are also some in the chloroplasts and mitochondria
What are enzymes?
Enzymes are proteins coded for by genes and they are involved in all the body’s metabolic processes including the synthesis of all non-protein molecules
Name some of the protein structures found in the body
DNA, estrogen (hormones), genes, DNA polymerase, haemoglobin, collagen, glycoproteins, antibodies, channel proteins
What is a triplet code?
When 3 bases code for one amino acid. They can be stop codes
What does the enzyme DNA helicase do?
Breaks the hydrogen bonds linking the base pairs of DNA
What must happen before transcription begins?
The RNA nucleotides must be activated. They are activated by the attachment of 2 extra phosphoryl groups.
What are activated nucleotides?
ATP, GTP, CTP, UTP.
List the steps of transcription.
1- H bonds between the complementary bases break, the DNA unwinds & unzips
2- Activated RNA nucleotides bind to their complementary bases on the exposed DNA with H bonds.
3- The two extra phosphates are released. The energy released here can be used to bind nucleotides together.
4- A strand of mRNA is produced that is complementary to the template strand & identical to the coding strand.
5- The strand of mRNA is released & leaves through a pore in the nuclear envelope.
What is transcription?
A process through which a complementary section of part of this sequence is made in the form of a molecule called mRNA
What is translation?
A process through which the mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide
List the steps of translation.
1- mRNA binds to a ribosome and two codons attach to the small sub-unit, the first is always AUG and this binds to a tRNA with the anticodon UAC and a methionine AA. ATP and enzymes are needed for the H-bonds to form between the codon and anticodon.
2- The tRNA with the next complimentary anticodon then binds
3- Peptide bonds form between the 2 adjacent AA’s
4- The ribosome moves along the mRNA reading the next codon
5- A third tRNA brings in another amino acid, the peptide bond is formed and the first tRNA is released to collect another AA
6- The polypeptide chain grows until a stop codon is reached. There are no tRNA’s for these codes UAA, UAC, or UGA. They are all “stop” codons.
