3 - DNA and Protein Synthesis Flashcards
Define virulent
Disease / has harmful effects
Who did the first experiment for DNA evidence?
Griffiths
Who did the second experiment for DNA evidence?
Avery, Macleod, McCarthy
Who did the third experiment for DNA evidence?
Hershey and Chase
What does DNA stand for?
Deoxyribonucleic acid
What does DNA consists of?
Phosphate group Nitrogenous base (ATCG) Deoxyribose sugar (5 carbon)
What did Chargaff et al discover?
Number of A = number of T
Same with C and G
Name the two types of bases
Purine and pyrimidine
Name the 2 purines
A and G
Name the 2 pyrimidines
T and C (both contain y)
Number of rings in purines
2
Number of rings in pyrimidines
1 ( 1 y 1 ring)
What does ATCG stand for
Adenine
Thymine
Guanine
Cytosine
What bond connects the bases
Hydrogen bonds
How many bonds connects the bases A and T
2
How many bonds connects the bases C and G
3 (George Clooney is 3 stars)
Describe a nucleotide
Phosphate , base , deoxyribose
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O /\ |
| / \
\ _ /
Which 2 directions do the nucleotides go?
Carbon 5-3 and Carbon 3-5
Which is bigger : purine or pyramidine
Purine as 3 hydrogen bonds
In which direction are the pentagons upside down?
3-5 or 5-3
Carbon 3-5
5 differences between DNA and RNA
Sugar Deoxyribose Ribose
Bases Thymine Uracil (pyrimidine)
Stands Double + base pairing Single
Helix Yes No
Length Big Smaller – no introns
Who did the DNA replication experiment?
Meselson and Stahl
What type of replication is DNA repiication?
Semi-conservative - half of original is bonded to new stands
Draw semi-conservative replication
11 II
1I I1
1I II II I1
Name the 3 types of rna
Messenger RNA
Ribosomal RNA
Transfer RNA
Describe rRNA (synthesises, found, shape, function)
Synthesised - nucleolus
Found - ribosomes (RER)
Shape - Globular
Function -Protein synthesis
Describe tRNA (synthesises, found, shape, function)
Synthesised - nucleolus
Found - cytoplasm
Shape - clover
Function -transfer AA
Describe mRNA (synthesises, found, shape, function)
Synthesised - nucleolus
Found - nucleus
Shape - single stranded
Function -DNA -> ribosome
What comes first: translation or transcription
Transcription - need to write script before you can translate it
Describe transcription (7)
- DNA helix unwinds to expose bases on template strand
- Template = 1 chain of DNA
- Catalysed by DNA helicase
- Break hydrogen bonds
- Free mRNA nucleotides oppose complementary bases
- RNA polymerase bonds them and copies them
- Leave through nuclear pores
What is splicing?
Removal of introns
What are introns?
Non-coding DNA
What are extrons?
Sequence containing coding DNA
Which strand is which? (sense)
A C T G
mRNA stand is anti-sense
Other one is sense strand
Summarise transcription
DNA to MRNA
Summarise translation
MRNA to Proteins
ATT CCG GGC
I
V
??????????????????
UAA GGC CCG
Codon 1 Codon 2 Codon 3
Define codon
Sequence of three nucleotides which form a unit of genetic code in a DNA or RNA molecule.
Name 3 characteristic of DNA
Universal coder
Non-overlapping
Degenerate
How is DNA the universal coder?
The same 3 bases codes for the same protein in all organisms
How is DNA non-overlapping?
Each base is only part of 1 triplet
How is DNA degenerate?
An amino acid is coded for by more than one triplet of bases
Processes in translation (7)
- Modified mRNA leaves nucleus and attaches to ribosome
- Ribosomes attaches to start codon
- tRNA molecule with complementary anticodon (to start codon) aligns opposite mRNA
- Ribosome moves along mRNA so others can attach
- Two delivered AA join by peptide bond
- Continue until reach stop codon
- Chain enters Golgi body
Define anticodon
Found on tRNA and sequence of nucleotides
Why does mitosis happen?
Cell growth and repair
Name the 6 stages of mitosis
Interphase Prophase Metaphase Anaphase Telophase and cytokinesis
Describe interphase
Chromosomes are thread like and cant be seen individually. DNA replicates
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Describe prophase
DNA condenses into discrete sister chromatins held together at the centromere.
The nuclear envelope breaks down and spindles form at opposite poles.
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. ⃝ X X ⃝ .
. = = .
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Where are spindles formed and at what stage?
Centrioles - prophase
Describe the metaphase
Sister chromatids are aligned at the equator
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. ⃝ ———– X ————— ⃝ .
. □ ———— X ———- □ .
. ———— X——— .
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Describe the anaphase
Spindle fibres contract and chromatids are separated. Chromosomes are pulled to opposite poles
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. ⃝ ————( (——- O .
. □———( (———– □ .
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Describe the telophase
Chromosomes are condoned off into distinct new nuclei in emerging daughter cells.
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. . II II . . II II . .
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Describe cytokinesis
The cytoplasm splits
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In mitosis, which two stages happen at the same time
Telophase and cytokinesis
What are the centrioles?
O I=I
What is the centromere
Where the spindle fibres attach to the chromosome
What are a pair of chromosomes called?
X X
Homologous chromosomes
What are the ends of the chromosomes called?
X ____here
Sister chromatids
Describe the process of DNA replication (9)
- DNA helicase breaks hydrogen bonds to form a replication fork
- Primase makes a primer
- DNA polymerase binds primer to make a new strand by moving along exposed bases
- DNA polymerase makes Okazaki fragments
- Primase makes a primer and DNA polymerase adds DNA in 5-3 direction
- Primer is added further down the strand then adds Okazaki fragments
- Exonuclease removes primers then DNA polymerase fills gaps with DNA
- DNA ligase seals strands to form a continuous strand
- Semi - conservative replication
What does DNA helicase do in DNA replication?
Breaks hydrogen bonds between the strands
What does primase do in DNA replication?
Makes primers
What is a primer in DNA replication?
Small piece on RNA
What does DNA polymerase do in DNA replication?
Binds the primer to synthesise a new strand and make Okazaki fragments
What does DNA ligase do in DNA replication?
Seal the strands
What does exonuclease do in DNA replication?
Remove the primer
Name the phases of meiosis in order
I1 P 1 M 1 A 1 T 1 P 2 M 2 A 2 T 2
What does meiosis produce?
4 daughter cells that AREN’T genetically identical
Define bivalent
The homologous chromosomes join
Equation for mitotic index
of cells in mitosis / total # of cells
Give 4 differences between mitosis and meiosis
Mitosis - Meiosis
- 2 daughter cells - 4 daughter cells
- Genetically identical - Not genetically identical
- Happens everywhere - Reproductive organs
- Diploid (23 pairs) -Haploid (23 total)
Name the 4 stages of the cell cycle
G1 - Growth 1 - new organelles / proteins made
S - DNA replication
G2 - Growth 2 - cytoplasm expands
M - Mitosis
Name two types of cancer
Benign
Malignant
Give 5 characteristics of benign cancer
- Grow slowly
- Well defined capsule
- Not invasive
- Low mitotic index
- Doesn’t metastasise
Give 5 characteristics of malignant cancer
- Grow rapidly
- Not encapsulate
- Invasive
- High mitotic index
- Metastasises (spread distantly)
Name 3 types of cancer treatment
Inhibit spindle fibre formation
Inhibit required enzymes
Competitive inhibition of nucleotides
Describe how MRNA is made
Helicase;
- Breaks hydrogen bonds;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to base pairing rule;
- RNA polymerase joins (RNA) nucleotides together;
- Pre-mRNA spliced to remove introns;
Describe the structure of proteins
Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is order of amino acids;
5. Secondary structure is folding of polypeptide chain due to hydrogen
bonding;
Accept alpha helix / pleated sheet
- Tertiary structure is 3-D folding due to hydrogen bonding and ionic /
disulfide bonds; - Quaternary structure is two or more polypeptide chains;
Why does DNA polymerase move in different directions on different strands (4)
- DNA has antiparallel strands
- Shape of the nucleotides is different / nucleotides aligned differently
- Enzymes have active sites with specific shape
- Only substrates with complementary shape / only the 3’ end can bind with active site of enzyme / active site of DNA polymerase
Explain why the replication of DNA is described as semi-conservative. (2)
Two copies of the original strand are made, but each strand contains half of the original strand.
Why is N15 further down the test tube than N14?
N15 is more dense.
Describe the role of tRNA in the process of translation.
5
1 - tRNA attaches to an AA on one end and has an anticodon on the other
2 - Transferred to a ribosome on a mRNA molecule
3 - Anticodon pairs with complementary codon sequence on mRNA
4 - More tRNA molecules line up along mRNA
5 - AA bond through a peptide bond
What would happen to a protein if there was a mutation in an intron?
Nothing - introns are removed by splicing so a protein isn’t made.
Describe and explain the appearance of one of the chromosomes in cell X. (3)
XX
There is a homologous chromosome, which is made from two chromatids. They are held together by the centromere. This has happened because DNA replication has occurred.
Identify one event that occurred during division 2 but not during division 1
Separation of (sister) chromatids / division of centromere
Name two ways in which meiosis produces genetic variation.
1 Independent segregation
2 Crossing of the chromatids
