topic 3 nucleotides and nucleic acids Flashcards
1
Q
3 components of nucleotides
A
- a pentose sugar
- a nitrogenous base
- a phosphate group
2
Q
what molecules are made from nucleotides
A
- RNA
- DNA
3
Q
3 components of DNA nucleotide
A
- deoxyribose
- A,T,C or G base
- a phosphate group
4
Q
what is deoxyribonucleic acid
A
(DNA) a type of nucleic acid that contains instructions needed to make proteins
5
Q
3 components of RNA nucleotide
A
- ribose
- A,U,G or C base
- a phosphate group
6
Q
what is a ribonucleic acid
A
(RNA) a type of nucleic acid that uses information from DNA to synthesise proteins
7
Q
bases can be grouped into 2 categories
A
- purines - larger bases that contain 2 carbon ring structures ( A and G)
- pyrimidines - smaller bases that contain 1 carbon ring structure (T and C)
8
Q
what base does RNA not contain
A
thymine it is replaced by uracil
9
Q
how do nucleotides join together to form a polynucleotide
A
- via a condensation reaction because water is released
- the phosphate group of one of the nucleotide forms a covalent bond with the hydroxyl group on the carbon 3 of the pentose sugar of another , creating a phosphodiester bond
10
Q
what is DNA made up of
A
- 2 polynucleotide strands wound around each other to form a double helix
- the 2 polynucleotide strands are held together by hydrogen bonds which form between bases on opposite strands
- the 2 polynucleotide strands are anti parallel
11
Q
features that allow DNA to pass genetic information from one generation to another
A
- sugar phosphate backbone - protects coding bases
- double stranded - allows strands to act as templates in DNA replication
- large molecules - stores lots of information
- double helix - makes molecule compact
- complementary base pairing - allows accurate DNA replication
- weak hydrogen bonds - allows strands to separate in DNA replication
12
Q
what are the complementary base pairs
A
- adenine pairs with thymine via 2 hydrogen bonds
- cytosine pairs with guanine via 3 hydrogen bonds
- a purine always pairs with a pyrimidine
13
Q
why does a smaller pyrimidine base bind to a larger purine base
A
- this arrangement maintains a constant distance between the 2 sugar phosphate backbones
14
Q
are the proportions of the complementary bases the same
A
yes
15
Q
when and how does chromatin form chromosomes
A
- before cell division chromatin which has a relatively open structure undergoes condensation to become tightly packed loops and coils to form chromosomes (chromosomes are visible under a microscope during cell division)
-before cell division all chromosomes are copied producing two identical DNA molecules known as chromatids which remain connected at a region called the centromere
16
Q
what are homologous chromosomes
A
pairs of chromosomes in a diploid organism (organisms w 2 sets of chromosomes e.g human) that have the same structure , size and same genes at the same positions (loci) but they may carry different versions (alleles) of those genes
17
Q
what happens to homologous chromosomes during sexual reproduction
A
homologous chromosomes pair up and exchange genetic material through a process called crossing over. this creates genetic diversity
18
Q
what are regions known as non coding sequences
A
large sections of DNA between genes that consists of repeating base units that do not code for proteins. ( all DNA not coding for proteins)
19
Q
what are introns
A
Non-coding sequences within genes, removed during RNA splicing
20
Q
stages of DNA replication
A
- The enzyme DNA helicase attaches to the DNA molecule and causes the hydrogen bonds between the complementary bases to break. This causes the two polynucleotide strands to separate from each other.
- Free nucleotides line up with their complementary bases on the DNA strands. At this stage, the free nucleotides are only held in place by hydrogen bonds between the complementary bases.
- The enzyme DNA polymerase moves down the molecule and catalyzes the formation of phosphodiester bonds between the activated nucleotides via condensation reactions in the 5’ to 3’ direction. The formation of phosphodiester bonds creates the sugar-phosphate backbone of the new DNA strand. When phosphodiester bonds form, the activated nucleotides lose their extra phosphate groups. The removal of these phosphate groups provides energy for the reaction.
- DNA ligase plays a crucial role in joining together fragments of newly synthesized DNA. On the lagging strand, DNA is synthesized in short segments called Okazaki fragments. DNA ligase seals the gaps between these fragments by forming additional phosphodiester bonds, ensuring that the lagging strand becomes a continuous strand.
- The process results in two identical copies of DNA, each consisting of one original DNA strand and one newly synthesized strand. This mechanism is known as semi-conservative replication.
21
Q
Every time a cell undergoes cell division all the DNA is copied what is this process called?
A
DNA replication
22
Q
what are mutations
A
When an incorrect base is inserted into the growing polynucleotide strand, changing the DNA sequence
Mutations are random and occur spontaneously
23
Q
Semiconservative replication
A
The DNA double helix separates into two poly nucleotide strands. Each strand is then replicated into a complementary new strand. One molecule is copied into two .each of the copies contain one strand from the original DNA molecule plus one new strand.
24
Q
conservative replication
A
A DNA double helix is formed containing two new strands. One molecule of DNA contains none of the original DNA and the other contains two strands of the original polynucleotide strands.
25
how was the experiment that proved DNA is replicated semiconservatively conducted
-all bases in the DNA contain the element nitrogen nitrogen atoms exist in two main isotopes and N14 and N15. N14 is the most common. atoms of N15 are slightly heavier
-scientists took a sample of E. coli bacteria, which have nitrogen atoms in the N14 form and extracted the DNA placed it in a solution and spun it in a centrifuge. The DNA moves down the solution and forms a band.The position of the DNA depends on how heavy the DNA is. This band was near the top.
-Scientists cultured bacteria in a growth medium, which only contain N15 then extracted the DNA and spun it in the centrifuge. It was heavier, so it formed a band near the bottom.
-the scientist took a sample of bacteria that have been growing on N15 and transferred it to an N14 growth medium and allowed them to replicate their DNA only once then spun it in a centrifuge. The band was in between the two previous bands. This proved that the DNA contained one strand with N14 and N15 and that it had not replicated conservatively.
-Then the scientist allowed the DNA to replicate one more time on N14 growth medium, then spun it on a centrifuge, an intermediate band and a band at the top of the tube formed. This proved that the DNA replicated, semiconservatively and ruled out all the theories, such as dispersive replication.
26
results for the experiment after spinning the centrifuge that proved DNA replicate semiconservatively
on N15 growth medium - band near the bottom
one replication on N14 growth medium after N15 - band in the middle
two replications on N14 growth medium after N15 - band near the top and middle
27
what is a gene
a short section of DNA that codes for a polypeptide ( a protein)
28
each gene is located at a specific position on a chromosome called..
a locus
29
What is a genome?
All the genes in the cell
30
what is a proteome
All the proteins produced by the genome of an organism
31
features of the genetic code
-universal-each DNA triplet codes for the same amino acid in all organisms
-non overlapping-each base in the DNA sequence is only read once
-Degenerate-most amino acids are coded for by more than one triplet
32
Three mRNA bases is known as
A codon
33
Three DNA bases is known as
A triplet
34
what is mRNA?
Mesenger RNA is a type of RNA synthesized during the process of transcription
35
what is the role of mRNA?
To carry genetic information from the DNA to the ribosomes
36
features of mRNA
- single-stranded, linear molecule
- Contains a base sequence, complementary to a DNA sequence
- Contains codons, which are sets of three bases that code for an amino acid
- Small enough to leave the nucleus
37
what is tRNA?
Transfer RNA is a type of RNA used in the process of translation
38
what is tRNAs role?
To transport amino acids to ribosomes to build up a polypeptide chain
39
features of tRNA
-single stranded molecule folded into a cloverleaf shape
-Uses hydrogen bonds between complementary base pairs to hold it in shape
-Contains a specific sequence of three bases at one end known as the anticodon
-Contains an amino acid binding site at the opposite end
40
where does transcription take place
nucleus
41
key events in transcription
-DNA helicase breaks the hydrogen bonds between the two strands.
This creates a section of single stranded DNA, exposing the bases
in the transcription start region
- The enzyme RNA polymerase binds to the promoter region on the DNA.
This identities where transcription should begin on the antisense strand
→ The antisense strand acts as a template for mRNA synthesis.
→ The other strand is called the sense strand.
→Free RNA nucleotides align with the DNA template through
complementary base pairing. They form hydrogen bonds with the bases
on the exposed nucleotides on one of the DNA strands
→ in the RNA molecule uracil pairs with adenine, while adenine pairs with
thymine, and cytosine pairs with guanine
- RNA polymerase catalyses the formation of phosphodiester, bonds
between adjacent RNA nuclecticles
→ A complementary mRNA strand is formed, carying the same base sequence as the DNA sense strand
→ The process ends when RNA polymerase reaches a stop codon detaches fron DNA and terminates transcription
→mRNA is released and detaches frim DNA and Dna rewinds into a double helix structure
→m RNA moves out through thr nucleus through a nuclear pore
42
where does translation occur
cystoplasm
43
transcription simply
involves creating an mENA copy of a gene from the DNA template
44
translation simply
process of decoding the information in messengerRNA to synthesize a polypeptide chain with the help of transfer RNA . this chain then folds into a functional protein
45
key steps in translation
- the riboseme attaches to the mRNA strand at the start codon (AUG)
- a tRNA molecule carrying a specific amino acid and with an specific anticodon (UAC) that is complementary to the start codon birds to the mRNA
-A second tRNA molecule with an anticodon complementary to the next mRNA codon, and also carrying a specific amino acid attaches to mRNA.
tRNA ts held in place by hydrogen bonds between the complementary base pairs on the mRNA and tRNA
- The amino acids carried by the first two tRNA molecules are linked together via a peptide bond using ATP catalyzed by the enzyme peptidyl transferase.
→ The first tRNA molecule detaches from mRNA and is free to collect another amino acid for future use
-The ribosome moves along mRNA, allowing anther tRNA molecule, which carries the next amino acid, to bind to the next codon on mRNA
- the process from the 4th and 5th step is repeated, which elongates the polypeptide chain
→ At any point during this process, two tRNA molecules can be attached
to the ribosome
- The sequence continues until the ribosone reaches the a stop codon
on the mRNA
- the completed polypeptide chain detaches from the ribosome
46
what is ATP involved in
energy transfer
temporarily holds energy and transfers it
47
why does ATP transfer energy instead of glucose
glucose releases much more energy than required
48
3 parts of ATP
- adenine - nitrogenous base
- ribose (pentose sugar)- 5 carbon sugar
- phosphate group- 3 phosphate groups
-Adenosine- adenine + ribose
-triphosphate - 3 phosphate groups
49
what is ATP a derivative of
nucleotide
50
how does ATP release a lot of energy
a small amount of energy breaks the covalent bond holding the last phosphate group in place and a lot of energy is released
51
how is ATP broken down
hydrolysis reaction
-when water is added it breaks down into adenosine diphosphate (ADP) and phosphate (Pi - not attached to carbon)
- catalysed by the enzyme ATPase (ATPhydrolase)
- releases energy
52
how is ATP resynthesised
condensation reaction
-a phosphate group and ADP join to release a water molecule
- catalysed by the enzyme ATP synthase
- process requires energy and traps chemical energy in the bond
- bcs a phosphate is being added back its a phopholylation reaction
53
features that allow ATP to work well as a immediate energy store
- hydrolysis of ATP releases less energy lost as heat bcs less energy is released than like glucose
- broken down in one step so energy is released quickly
- rapidly resynthesised
-the inorganic phosphate can phosphorylate (add to other molecules) making them more reactive
- bonds between phosphate groups are unstable so have low activation energy and easily broken
- soluble so easily transported
