nucleic acids Flashcards
(49 cards)
1
Q
features of nucleotides
A
- repeating monomers forming nucleic acids
- large, contained in nucleus of cells
- important in the storage and transfer of genetic info to make proteins
- form polynucleotides by forming phosphodiester bonds
- become phosphorylated nucleotides when they contain more than one phosphate group
- help regulate many metabolic pathways
2
Q
nucleotide structure
A
phosphate group, 5C (pentose) sugar (deoxyribose/ribose), nitrogenous base
3
Q
how are polynucleotides formed
A
- condensation reactions between nucleotides form strong phosphodiester bonds
- phosphodiester bonds form between the phosphate group of one nucleotide and the C3 on the next
4
Q
how are polynucleotides broken down
A
-hydrolysis reactions use a molecule of water to break the phosphodiester bonds between nucleotides
5
Q
where is dna found in eukaryotes
A
- nuclei of cells
- each large DNA molecule is wound around histone proteins into chromosomes
- there’s a loop of dna (without histones) inside mitochondria and chloroplasts
6
Q
where is dna found in prokaryotes
A
- in a loop in the cytoplasm, not enclosed in a nucleus
- not wound around histones (described as naked)
7
Q
dna features
A
- large, stable
- double stranded molecule
- hereditary material
- carries coded instructions used in the development and functioning of all living organisms
- contains genes that code for proteins
8
Q
what are the purine bases and their features
A
- adenine and guanine
- large
- two ring structure
9
Q
what are the pyrimidine bases and their features
A
- thymine, cytosine, uracil
- smaller
- one ring structure
10
Q
phosphate group features
A
- inorganic molecule (not made of C atoms)
- negatively charged
11
Q
dna structure
A
- polymer
- made of many monomeric units, nucleotides
- strands are antiparallel
- large
- covalent phosphodiester bonds between nucleotides form
—> broken when polynucleotides break down
—> formed when polynucleotides are synthesised
12
Q
antiparallel meaning
A
- the two dna strands run in opposite directions
—> refers to the direction C3 and C5 on deoxyribose are facing - 5’ end - where phosphate group is attached to C5 on deoxyribose
- 3’ end - where phosphate group is attached to C3 on deoxyribose
13
Q
hydrogen bonds
A
- antiparallel strands are joined to eachother by H bonds between bases
- A and T: 2 H bonds
- (RNA) A and U: 2 H bonds
- G and C: 3 H bonds
- H bonds allow molecule to unzip for transcription and replication
14
Q
why do purines always pair with pyrimidines
A
- gives equal sized rungs on the dna ladder
—> these can then twist into the double helix
——> gives molecule stability
15
Q
what is the genome
A
the genome of every cell in an organism carries the coded instructions to make and maintain that organism
16
Q
what are the reasons for dna replication
A
- cell division - new cells need new DNA for growth and repair, also so each new daughter cell recieves the full set of instructions
- reproduction - gametes require dna to pass on genetic info
17
Q
what does semi conservative replication mean
A
- each of the 2 identical dna molecules produced contain one old strand and one new strand
18
Q
role of dna helicase
A
breaks the hydrogen bonds between nucleotides and unwinds the dna molecule
19
Q
role of dna polymerase
A
forms the phosphodiester bonds between nucleotides
20
Q
role of dna ligase
A
joins the fragments of dna, complementary to the lagging strand, together
21
Q
leading strand
A
- parent strand of dna which runs in the 3’ to 5’ direction
- able to be replicated continuously by dna polymerase
22
Q
lagging strand
A
- parent strand of dna which runs in the 5’ to 3’ direction
- replicated discontinuously (in fragments)
23
Q
steps in dna replication
A
- double helix is untwisted, a bit at a time
- H bonds between nucleotides are broken - catalysed by dna helicase
- results in 2 single strands of dna with exposed nucleotide bases
- free phosphorylated nucleotides in the nucleus pair up and bond with the exposed complementary bases
- dna polymerase catalysts the addition of the new bases, in the 5’ to 3’ direction
- leading strand is synthesised continuously whereas the lagging strand is in fragments that are later joined and catalysed by ligase enzymes
24
Q
product of dna replication
A
- 2 dna molecules
- each are identical to eachother and the parent molecule
- each molecule contains one old strand and one new strand
25
when do mutations occur
during dna replication
26
what are point mutations
- **small** errors occur (e.g the wrong nucleotide is inserted)
- happen approx in every 1 in 10^8 base pairs
- often edited out by enzymes later in the replication process
—> they **proofread** and edit out incorrect nucleotides
27
what happens when small errors aren’t edited out of the replication process
a slightly different version of the original gene may be produced (an **allele**)
—> can be beneficial, detrimental or have no impact
28
what are beneficial and detrimental changes due to errors
BENEFICIAL - change has coded for a different AA which has changed the overall protein structure in a **positive** way
- has been **advantageous** for the organism
- e.g change in fur colour allows for better camouflaging
DETRIMENTAL - overall protein structure has changed in a **negative** way
- has been **disadvantageous** for the organism
- e.g change in enzyme structure meaning the organism can no longer digest key nutrition
29
rna features
- shorter and smaller than dna
- single stranded
- bases are C, G, A, U
- less stable than dna
- **ribose** pentose sugar
30
rna function
retrieves info from dna to code for proteins synthesised in the cell’s ribosomes
31
how do ribose and deoxyribose differ
ribose has an OH attached to the bottom of C2
deoxyribose has a H attached to the bottom of C2
32
what is the genetic code
the sequence of bases along an organisms dna that tell the cell how to make a specific protein
33
what is a codon
a sequence of 3 consecutive nucleotides in a dna/rna molecule that codes for a specific AA
34
features of the genetic code
- **near universal:** in almost all living organisms, the same dna triplet of bases codes for the same AA
- **degenerate:** each AA is coded for by more than one triplet
—> may reduce the effect of point mutations because a change in one base of the triplet could produce another base triplet that still codes for the SAME AA
- **non-overlapping:** each base is only part of one triplet/codon and each triplet/codon codes for just one AA
35
structure of ATP
3 phosophate groups
1 ribose sugar
1 adenine nitrogenous base
36
what does ATP stand for
adenosine triphosphate
37
function of ATP
- used to power most energy requiring cellular reactions
- transfers E from sites of respiration-> parts of the cell that **require** E
- used by cells to transfer glucose molecules in smaller, more **useful** amounts
38
hydrolysis of atp
- when cell **needs** energy
**ATP + H2O —> ADP + Pi (+ energy)**
- 3rd inorganic phosphate group is released
- catalysed by enzyme ATP **hydrolase**
- the E released is used to perform **work** in the cell
- can be **coupled** to other reactions within cell that need E
39
resynthesis of atp
- resynthesised by the **condensation** of ADP and Pi
**ADP + Pi (+ energy) —> ATP + H2O**
- catalysed by enzyme ATP **synthase** during photosynthesis or respiration
40
mrna structure
- **single** stranded
- contains a ribose pentose sugar
- contains C, G, A, **U**
- small enough to leave nuclear pores
- easily broken down
- **complementary** to dna code
41
mrna function
- used to transfer the DNA **code** from the nucleus -> cytoplasm
- once in cytoplasm, it **associates** with the ribosomes
- used to determine the sequence of AAs during **protein synthesis**
42
trna structure
- small, single stranded
- **specific** to one AA
- folded into a **clover leaf** shape with one end of the chain slightly longer
—> this longer section is **attached** to an **AA**
- each has a sequence of 3 bases called an **anticodon**
—> these are **complementary** to codons on the mrna molecule and it attaches here
43
why does transcription happen
the instructions inside genes (on chromosomes) cannot pass out of the nucleus, so a **copy** of each gene has to be transcribed into a **length of mrna**
44
transcription steps
1. **helicase** breaks H bonds between bases
2. **polymerase** moves along one of the strands (template strand)
3. polymerase matches up **complementary** rna nucleotides
4. as rna nucleotides join, **pre mrna**
5. dna behind rna polymerase **rejoins** into double helix
6. when rna polymerase reaches a **”stop”** codon, chain is **terminated** , pre - mrna detaches
45
result of transciption
pre - mrna, has the **complementary** sequence to the non-template/coding strand except all T vases are replaced with **U bases**
46
what is the template strand also known as
the antisense strand or the noncoding strand
47
what is the non template strand
it’s the **coding** strand because its sequence will be the same as that of the **new rna** molecule
48
when does translation happen
when a molecule has been transcribed and it has then moved out of the nucleus (via a nuclear **pore**) to begin translation attached to a **ribosome** in the cytoplasm
49
translation steps
1. mrna attaches to a ribosome at the **start** codon
2. trna attached to the mrna
4. ribosome moves along mrna, reading the code. when 2 AAs are adjacent, a **peptide** bond forms between them
5: ATP is needed for this polypeptide synthesis
6. first trna is **released** and can collect another AA
7. process is repeated till a “stop” codon is released
8. mrna **breaks down** once polypeptide has been assembled
9. newly synthesised protein is helped to fold correctly into its 3D shape **tertiary structure**
