Bio Unit 1.5 - Nucleic Acids Flashcards
What are nucleic acids (a polymer) made out of?
Monomers called nucleotides
Three components of nucleotides
Phosphate group, pentose sugar, nitrogenous/organic base
Two groups of organic bases
Purine bases, pyramidine bases
What is the pentose sugar in RNA?
ribose
What is the pentose sugar in DNA?
deoxyribose
What do autotrophic organisms do?
Convert other forms of energy into chemical energy
Chemoautotrophic organisms
Bacteria and Archaea use energy from oxidation of electron donors
Photoautotrophic Organisms
Green plants use light energy in photosynthesis
Hetetrophic Organisms
Organisms that derive chemical energy from food
Molecule that makes energy available when needed is…
Adenosine Triphosphate
How much ATP do we make and break down everyday but how much does the body contain?
50 kg, 5g contained
When is ATP synthesised and broken down?
Synthesises when energy is made available, like in mitochondria
Broken down when energy is needed, such as in muscle contraction
What is ATP and its structure?
A nucleotides with base adenine, sugar ribose and three phosphate groups
What happens to ATP when energy is needed in a living organism?
ATPase hydrolyses bond between 2nd and 3rd phosphate groups in ATP making adenine diphosphate and an inorganic phosphate ion, releasing chemical energy
How much energy is released when every mole of ATP is hydrolysed and the bond is broken?
30.6kJ
What is the name of the ATP to ADP reaction that releases energy?
Exergonic
Is the ATP to ADP reaction reversible?
Yes
What happens in the condensation reaction between ADP and the inorganic phosphate ion?
Catalysed by ATP synthesise, ADP and inorganic phosphate ion combine to make ATP and water, requires energy input of 30.6kJ
What is the name of the reaction which makes ATP and water?
Endergonic
The addition of phosphate to ADP is called?
Phosphorylation
Where does ATP transfer energy from and to?
From energy rich compounds like glucose to cellular reactions where it is needed
What would uncontrolled release of energy from glucose do and what is the solution for this?
Produce a temperature increase that would destroy cells. Instead, living organisms release energy gradually in small steps called respiration, producing ATP
Why is the hydrolysis of ATP to ADP a better supplier of energy than the breakdown of glucose?
Involves a single reaction whereas breakdown of glucose involves may intermediates and takes longer for energy to be released
Why (in terms of enzymes) is ATP to ADP better then a glucose breakdown?
Only involves one enzyme, many needed to release energy from glucose
How much energy is released from ATP compared to glucose?
Energy released in small amounts but glucose contains large amounts of energy that is released all at once
Why does ATP providing a common source of energy for many different chemical reactions good?
Increases efficiency and control by the cell
What does ATP do in metabolic processes?
To build large complex molecules from smaller, simpler molecules such as DNA synthesis from nucleotides, proteins from amino acids
What is the role of ATP in active transport?
To change the shape of carrier proteins in membranes and allow molecules or ions to be moved against a concentration gradient
What is the role of ATP in secretion?
Helps with the packaging and transport of secretory products into vesicles in cells
Structure of DNA (components)
2 polynucleotide strands wound round each other in a double helix, deoxyribose pentose sugar, four organic bases: guanine, cytosine, adenine, thymine
What forms the backbone of DNA?
Deoxyribose sugar and phosphate groups on the outside of DNA molecules
Complementary base pairings in DNA
A+T, C+G, hydrogen bonds join the bases and form complementary pairs
A+T joined by 2 hydrogen bonds
C+G joined by 3 hydrogen bonds
Hydrogen bonds maintain double helix shape
What is DNA molecule coiled within?
Chromosome
Direction of strands in DNA
Antiparallel
DNA is suited to its functions because…
Very stable molecule and information content passes unchanged through generations, large so carries a lot of genetic information, 2 strands able to separate as they are held by hydrogen bonds, genetic information protected by structure
Structure of RNA
single stranded polynucleotide, pentose sugar ribose, bases adenine, guanine, uracil, cytosine
Three types of RNA
messenger RNA, ribosomal RNA, transfer RNA
mRNA
synthesised and carries genetic code from DNA to ribosomes in cytoplasm. Lengths of mRNA related to lengths of the genes from which they were transcribed
rRNA
found in cytoplasm, ribosomes (site of translation of genetic code into protein) made from rRNA and protein
tRNA
Folds so that there are base pairings forming complementary pairs
3’ end has base sequence CCA where specific amino acid carried by molecule is attached
Carries anticodon
Carries specific amino acids to ribosomes in protein synthesis
Where is DNA in eukaryotes and prokaryotes?
Enclosed in nuclei, free in cytoplasm
2 main roles of DNA are…
Replication and protein synthesis
How does DNA help protein synthesis?
Sequence of bases represents information carried in DNA and determines sequence of amino acids in proteins
Three possibilities of DNA replication
Dispersive, Semi conservative, Conservative
Semi conservative replication
Parental double helix separates into two strands each of which acts as a template for synthesis of a new strand
What’s the experiment that figured out semi conservative replication?
Meselson-Stahl Replication
Stage 1 of semi conservative replication
Helices breaks hydrogen bonds holding base pairings together and DNA unwinds catalysed by helices and the two strands separate
Stage 2 of semi conservative replication
Polymerase catalyses the condensation reaction between 5’ phosphate group of a free nucleotide and 3’OH on growing DNA chain.
Each chain acts as a template and free nucleotides are joined to their complementary bases
Gene
A section of DNA on a chromosome which codes for a specific polypeptide
What does the base sequence direct?
Which amino acids join together
Three bases code for…
One amino acid
Introns
Non coding nucleotide sequence in DNA and pre-mRNA that is removed from pre-mRNA to produce mature mRNA
The genetic code is a …
Triplet code
How many possible codes are there and how many amino acids are found in proteins?
64, 20
Transcription (part of protein synthesis) - occurs in the nucleus
One strand of DNA acts as a template for the production of mRNA, a complementary section of part of a DNA sequence
Exons
Coding region in the nucleotide sequence of DNA and pre-mRNA that remains present in mature mRNA after introns have been removed
Translation - occurs on ribosomes in the cytoplasm
mRNA acts as a template to which complementary tRNA molecules attach and amino acids they carry are linked to form a polypeptide
Process of protein synthesis
DNA, transcription in nucleus, mRNA, translation at ribosome, polypeptide
Sequence of events for transcription up to alignment
Helices breaks hydrogen bonds between bases, two strands separate, polymerase binds to template strand at the beginning of sequence to be copied, free RNA nucleotides align opposite template strand based on complementary relationship between bases in DNA and free nucleotides
Sequence of events of transcription after alignement up to rewinding
Polymerase moves along DNA forming bonds that add RNA molecules, RNA strand grows, resulting in synthesis of a molecule of mRNA alongside unwound portion of DNA, DNA strand rewind to reform the double helix
Sequence of events of transcription after rewinding
Polymerase separates template strand when it reaches ‘stop’ signal, production of the transcript is complete and the newly formed RNA detaches from DNA
What happens during translation?
sequence of codons on mRNA is used to generate a specific sequence of amino acids forming a polypeptide. Takes place on ribosome and involves tRNA
Two subunits of ribosome
- Larger subunit has 2 sites for attachment of tRNA molecules so two tRNA molecules are associated with a ribosome at any time
- Smaller subunit binds to the mRNA
What happens to second tRNA during initiation?
Attaches to the other attachment site and the codon and anticodon bond with hydrogen bonds
First stage of Translation
Initiation- ribosome attaches to a start codon, first tRNA attaches to the ribosome, 3 bases of the codon on the mRNA bond to 3 complementary bases of the anticodon of tRNA with hydrogen bonds
2nd stage of Translation
Elongation, two amino acids are close for a ribosomal enzyme to catalyse formation of peptide bond between them
3 point during elongation?
first tRNA leaves ribosome and returns to cytoplasm to bind to another copy of amino acid, ribosome moves one codon along mRNA strand, next tRNA binds
3rd stage of Translation?
Termination, sequence repeats until ‘stop’ codon reached
What is a polysome?
Several ribosomes bind to single mRNA strand each reading the coded information at the same time
What does anticodon on tRNA determine?
which amino acid the tRNA molecule carries
tRNA and amino acid activation
tRNA released from ribosome, free to collect another amino acid from amino acid pool in cytoplasm, energy from ATP needed to attach amino acid to tRNA
