Heredity Flashcards
(45 cards)
1
Q
The discovery of DNA
A
- Rosalind Franklin took the first clear X-ray diffraction image of DNA in 1952
- confirmed the spiral nature of DNA
2
Q
Eukaryotic cells
A
DNA bound to proteins in chromosomes in nucleus enclosed in nuclear membrane
Also found in mitochondria and chloroplasts
3
Q
Prokaryotic cells
A
Unbound circular DNA in nucleoid membrane - not bound by a nuclear membrane
4
Q
DNA - deoxyribonucleic acid
A
smaller repeating subunits of nucleotides
double stranded
- bases held by weak hydrogen bonds
- nucleotides between sugar and phosphate units are held together by phosphodiester bonds
5
Q
Nucleotide consists of
A
- phosphate group
- deoxyribose sugar / ribose sugar
- nitrogenous base
6
Q
4 bases for DNA
complementary base pairs
A
- cytosine and guanine (3 H+ bonds)
- adenine and thymine (2 H+ bonds)
7
Q
Nucleotides
A
building blocks of DNA
held together by:
strong chemical bonds - phosphodiester bonds
- between sugar and phosphate units
8
Q
RNA - ribonucleic acid
A
uracil replaces thymine
one stranded
9
Q
the purpose of DNA replication
A
- duplicate the code it carries - passed to daughter cells
preparation for cell division, mitosis and meiosis
10
Q
DNA replication - eukaryotic cells
A
chromosomes gain a sister chromatid - x2 stranded
11
Q
when does DNA replication occur?
A
S phase of interphase of the cell cycle
12
Q
The process of DNA replication
1. - unwinding of DNA
A
- DNA helicase (enzyme) unwinds and separates the double stranded DNA by breaking the weak hydrogen bonds between the nucleotide bases, this exposes the nucleotide bases for replication
- the replication fork forms at the junction where the DNA strands separate
- As replication progresses, the replication fork moves along the parental DNA, continuously unwinding it
13
Q
The process of DNA replication
2. - priming the template strand
A
- the enzyme primase attaches a short sequence of RNA primer (at short intervals on lagging strand) to the exposed DNA strand
- this primer signals DNA polymerase where to start adding new nucleotides
14
Q
The process of DNA replication
3. - nucleotide addition
A
- DNA polymerase removes the RNA primers and then the free complementary nucleotide bases attach to the exposed bases on each template strand with the help of DNA polymerase
- since DNA strands are antiparallel, DNA polymerase moves in opposite directions on the two strands, leading and lagging
15
Q
The process of DNA replication
4. - sealing and rewinding
A
- the enzyme DNA ligase seals the newly synthesised Okazaki fragments on the lagging strand, forming a continuous DNA strand, then rewind into a double helix
16
Q
The process of DNA replication
5. - result
A
is the production of two identical DNA molecules
17
Q
leading strand
A
- DNA polymerase synthesises continuously in the same direction as the replication fork (towards the replication fork)
- synthesis continuous
18
Q
lagging strand
A
- DNA polymerase sythesises in short fragments (okazaki fragments) in the opposite direction (away from the replication fork)
- synthesis discontinuous
19
Q
where is DNA found in eukaryotes
A
DNA bound to proteins in chromosomes in nucleus enclosed in nuclear membrane
Also found in mitochondria and chloroplasts
20
Q
where is DNA found in prokaryotes
A
unbound circular DNA in nucleoid region of the cytosol - not bound by a nuclear membrane
21
Q
Protein synthesis consists of
A
transcription
translation
22
Q
Essential materials needed for protein synthesis
A
- enzymes
- codons
- amino acids
- nucleic acids
23
Q
what is transcription
A
synthesis of mRNA using stored DNA
24
Q
transcription process
A
- one section of DNA called a gene, is unwound and separated ready for copying
- a promoter attaches to help the DNA template strand to separate from the non-template strand, initiating transcription
- RNA polymerase (does not require primer) moves step by step along the DNA molecule, separating the two strands, only the template strand (also known as the non-coding strand) is copied
- the other strand - known as the coding strand - has the same code as the mRNA
- RNA polymerase then attaches the RNA nucleotide that’s complementary to each base (synthesises the mRNA in a 5’ to 3’ prime direction, anti-parallel to the template strand)
- After RNA polymerase enables elongation of the strand, mRNA molecule detaches as pre-mRNA
- pre-mRNA requires processing before it exits nucleus via nuclear pores
- stretches of non- coding DNA (introns) are removed and the remaining stretches of DNA (exons) join to form mature mRNA
25
translation
RNA directed synthesis of a polypeptide
Ribosomes are mostly composed of ribosomal RNA (rRNA), - non-coding
26
translation - Initiation
beginning - ribosome bond to mRNA
- a ribosome binds to a molecule of mRNA. It 'reads' the mRNA nucleotidees in threes
- a start codon (AUG) signals the start of translation. Two codons enter and are bound to the ribosome. Following initiation, only one codon enters and is translated at a time
27
translation - Elongation
creating polypeptide chain (start codon)
- a tRNA molecule, which includes an anticodon, is attracted to the corresponding codon (on mRNA) due to complementary base pairing
- on the other side of the tRNA molecule is the amino acid specified by the codon
- as one codon is read and exits the ribosome, another one slides in, to be read. tRNAs transfer the amino acids to the mRNA - ribosomal complex in the order specified by the codons of mRNA
- mRNA is moved through ribosome in one direction only
- Once tRNA dropped off its amino acid, returns to cytoplasm to reload with same type of amino acid
- same amino acids are coded for by more than one codon
28
translation - Termination
stops and polypeptide chain released from ribosome
- elongation continues until a stop codon in the mRNA entered the ribosome
- nucleotide base triplets, UAG, UAA and UGA do not code
29
transfer RNA
- amino acids delivered to ribosome by transfer RNA (tRNA)
- RNA molecules that have anticodons
- anticodons are complimentary to codons in mRNA
- Different tRNA's have different anticodons and can carry different amino acids to ribosomes
- determines amino acid they carry on the other end of the molecule
- clover shaped loop structure
- reactivated with a new amino acid after translation
- proteins are built from a section of 20 amino acids
- the amino acids are linked together by peptide bonds to form polypeptide chain
30
messenger RNA
- simple strand
- broken down after translation
- transcribed form DNA in the nucleus and posted out to the ribosome for translation
- codons are complimentary to DNA triplets - anticodons
31
DNA tools
- restriction enzymes
- DNA ligase
- DNA polymerase
- Primers
32
Restriction enzymes
- moves along DNA until finds recognition site - cuts at the recognition site
creates smaller pieces, called restriction fragments
two types of cuts
33
blunt end cut
straight cut, no overhang
34
sticky end cut
cuts at different spots
more often used
one strand has overhanging complementary bases
35
DNA ligase
important in DNA replication
seals/reassembles DNA fragments - ligation
36
DNA polymerase
class of enzymes that synthesise new strands of DNA
adds free nucleotides to make a new strand
used in amplifying DNA during PCR
37
Primers
short fragments of single stranded DNA or RNA
signal for the polymerase to begin synthesis
38
DNA base techniques
methods to analyse, modify and manipulate DNA bases
39
Amplification
- increase number of copies of a DNA sequence for further lab use
- most common method is PCR
40
PCR - polymerase chain reaction brief description
amplifies a specific DNA sequence by repeatedly heating and cooling the sample to enable DNA denaturation, primer binding, and enzymatic replication, producing millions of copies
- replicated many times
- increase copies a lot
- has requirements
41
PCR - 1. Denaturation
- DNA double strand is heated up to around 95°C to separate into single strands by breaking the bonds between the bases
42
PCR - 2. Annealing
Temperature is lowered to 50 - 60°C so primers can bind to their complementary sequences, by joining back the H bonds
43
PCR - 3. Extension/elongation
DNA taq polymerase attaches free nucleotides to the end of primers - can not work at high temperatures - 72°C
44
PCR - 4. Repeat cycle
These steps repeated for multiple cycles, exponentially amplifying the target DNA sequence
e.g. 4, 8, 16, 32
45
Gel electrophoresis
- extract DNA samples to be analysed from an organism's cells, than cut the strands withe restriction enzymes
- pour agarose, jelly like material into a tray, solution sets as gel
- make wells in gel and add a buffer solution, this solution covers the entire gel and the wells imbedded
- place DNA samples in well with the use of pipettes
- run a current through the gel electrophoresis machine, through the gel, molecules (because negative) travel towards the positive end, the smaller molecules move faster (negative molecules are repelled by positive electrode and travel away from beginning)
- analyse the data and any patterns shown by the gel electrophoresis - under ultraviolet
