1.5 - Nucleic acids Flashcards
(a)
The structure of nucleotides
The general structure of a nucleic acid consists of a pentose sugar a phosphate group and a nitrogenous base
(b)
The importance of chemical energy in biological processes
In biological systems it is chemical energy that makes changes because chemical bonds must make or break for reactions to happen.
(c)
ATP as an energy carrier
ATP is called the ‘universal energy currency’ as it is used to provide energy for all biochemical reactions in all living organisms.
(c)
ATP and its use in the liberation of
energy for cellular activity
ATP releases energy in one hydrolysis reaction controlled by one enzyme. ATP releases energy in small, usable amounts. ATP travels easily to where it may be used for secretion, muscle contraction, nerve transmission or active transport.
(d)
The structure of ATP
Adenine
Ribose
Three phosphate groups
(e)
DNA bases
Purines- adenine and guanine
Pyrimidines- cytosine and thymine
(e)
DNA structure
DNA is made from one strand of nucleotides linked by hydrogen bonds between the bases to another strand that runs antiparallel to the first.
(e)
Complementary base pair rule
Adenine and Thymine
Guanine and Cytosine
This complementary base pairing links the two strands and a double helix is formed.
(f)
The similarities and differences in the structure of RNA and DNA
RNA
Ribose sugar
Single stranded
A,U,C,G bases
Short polynucleotides
**
DNA**
Deoxyribose sugar
Double stranded
A,T,C,G bases
Long polynucleotides
(f)
Three types of RNA found in cells
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
(f)
Function of messenger RNA (mRNA)
Made as a complementary copy of the DNA genetic code in the nucleus during transcription. The molecule length is related to the length of the gene transcribed. It attaches to a ribosome in the cytoplasm.
(f)
Function of ribosomal RNA (rRNA)
Forms ribosomes.
(f)
Function of transfer RNA (tRNA)
carries an amino acid at the 3’ end and an anticodon arm to attach to the mRNA.
(g)
Major function of DNA; replication
DNA comprises two complementary strands, the base sequence of one strand determining the base sequence of the other. If two strands of a double helix are seperated, two identical double helices can be formed, as each parent strand acts as a template for the synthesis of a new complementary strand.
(g)
Major function of DNA; protein synthesis
The sequence of bases represents the information carried in DNA and determines the sequence of amino acids in proteins.
(h)
Semi-conservative replication of DNA
The replication of DNA to produce two new DNA molecules which both contain one new strand and one old strand from the original DNA molecule.
(h)
Role of DNA polymerase in semi-conservative replication
It catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.
(h)
Role of DNA helicase in semi-conservative replication
It catalyses the unzipping of double-stranded DNA into two single strands, each of which acts as a template.
(i)
Genetic code
The genetic code is a linear, universal code for the production of polypeptides.
(j)
The triplet code for amino acids
A specific sequence of three nucleotides (codon) on a molecule of DNA or RNA codes for a particular amino acid in protein synthesis.
(k)
Exons
Regions of DNA that contain the code for proteins and between the exons are regions of non-coding DNA called introns
(l)
Transcription
First stage of protein synthesis and the formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA
(l)
Transcription process
- DNA helicase unwinds DNA by breaking hydrogen bonds, exposing bases.
- RNA polymerase binds to the template strand at the gene’s start.
- Free RNA nucleotides pair with complementarty DNA bases:
C → G, G → C, A → T, U → A - RNA polymerase forms bonds, synthesising mRNA.
- DNA rewinds behind RNA polymerase.
- At a stop signal, RNA polymerase detaches; mRNA is released.
(m)
Translation
Second stage of protein synthesis which takes place in the ribosomes. mRNA used as a template for the attachment of tRNA molecules with complementary anticodons. Amino acids carried on adjacent tRNA molecules are joined to form a polypeptide chain
(m)
Translation process
- mRNA attaches to groove between subunits of ribosome
- Ribosome moves along mRNA until ‘start’ codon reached
- Amino acid-tRNA complex anticodon attaches to complementary mRNA codon via hydrogen bonding. Another complex binds
- Peptide bond forms between adjacent amino acids in the complexes
- Ribosome moves along one codon and release empty tRNA. Process continues to form polypeptide chain until ‘stop’ codon is reached.
(n)
The ‘one gene - one polypeptide’ hypothesis
The theory that each gene encodes a single protein.
(o)
The further modification and combination of some polypeptides
After translaton, polypeptides are further modified by adding carbohydrates, lipids or phosphates and different polypeptides may be combined.
