DNA Flashcards
4 basic parts of the nucleus:
- Nuclear membrane (continuous with Endoplasmic
Reticulum and has pores) - Nucleoplasm contains free nucleotide bases
- Nucleolus manufactures and contains ribosomal RNA
(rRNA) - Chromatin network contains DNA. Unwinds to form
chromosomes.
Nucleic acids are made up of?
smaller units (monomers) called nucleotides
Types of nucleic acids?
1) DNA -deoxyribonucleic acid
2) RNA -ribonucleic acid
Each nucleotide is made up of:
- A nitrogenous base (NB)
- A sugar portion (S)
- A phosphate portion (P)
Functions of DNA
1) Nuclear DNA also transmits hereditary characteristics from parents to offspring.
2) Nuclear DNA controls the synthesis of proteins (including enzymes – modified proteins that control metabolic activities in a cell)
∴ DNA controls the structure and functioning of cells.
e.g. Chloroplastic and Mitochondrial DNA control protein synthesis within these organelles.
2 groups of nitrogenous bases:
1) Purines (adenine and guanine) - bigger
2) Pyrimidines (cytosine and thymine) - smaller
What is the sugar molecule of DNA?
deoxyribose
What is the purpose of a sugar-phosphate bond?
The sugar molecule of a nucleotide attaches to the phosphate ion of another by sugar-phosphate bonds —>forming a long chain of sugars and phosphates.
Nitrogenous base pairs:
Complementary base pairs:
1) Adenine (bigger) with thymine (smaller) = 2 H-bonds
2) Guanine (bigger) with cytosine (smaller) = 3 H-bonds
The nitrogenous bases are held together by weak hydrogen bonds resulting in ?
a double stranded structure
ladder-like DNA molecule twists so that 1 strand coils around the other forming …
a double helix structure
Definition of gene
a small portion of DNA which carries the genetic code for the formation of a particular trait or characteristic. It also carries the code for proteins.
Most sections of DNA don’t carry any codes at all =
non-coding DNA
Who proposed the double helix structure and how?
Rosalind Franklin and by from X-ray diffraction images.
Who won nobel peace prize for the discovery of the double helix structure?
James Watson, Francis Crick & Maurice Wilkins
How did James Watson and Francis Crick get the double helix structure and what did they discover?
Rosalind Franklin’s partner Maurice Wilkins showed these images to James Watson and Francis Crick.
Watson and Crick found that DNA contained similar amounts of adenine and thymine and also similar amounts of cytosine and guanine which gave them the idea of complementary base pairing which allows DNA to make exact copies of itself.
Types of RNA
1) Ribosomal RNA (rRNA) makes up the ribosomes in
the cytoplasm of the cell. They catalyse the assembly
of amino acids to form proteins.
2) Messenger RNA (mRNA) found in the nucleus of the
cell but moves out of the nucleus and attaches to the
ribosomes in the cytoplasm.
3) Transfer RNA (tRNA) found in the cytoplasm.
Functions of RNA
all types play a role in protein synthesis
Structure of RNA
1) It is single stranded
2) It is not coiled
3) The sugar in it is ribose (not deoxyribose)
4) Thymine is replaced by uracil
5) The chains are shorter
Similarities RNA and DNA
1) both contain a sugar alternating with a phosphate
2) both play a role in protein synthesis
3) both contain nitrogenous bases adenine, thymine, guanine and cytosine
Define DNA replication
The process where DNA makes an exact copy of itself.
When does DNA replication occur?
during interphase in the cell cycle (before mitosis and meiosis)
Why does DNA replication occur?
- Each chromosome can make an identical copy of itself. This increases the number of chromosomes so that they can be shared between the cells resulting from cell division.
- The nucleus can split into 2 and each cell will have the same number of chromosomes.
- In mitosis, the resulting cells will be identical to each other and the parent cell.
How does DNA replication occur?
- The double DNA helix unwinds
- Weak H bonds between nitrogenous bases break and the 2 strands of DNA unzip/ separate
- Each original DNA strand serves as a template to form a new strand by attaching to free nucleotides from the nucleoplasm
- This forms complementary strands (A to T and C to G)
- Each DNA molecule consists of 1 original strand and 1 new strand. The result is 2 genetically identical DNA molecules
Definition of DNA profiling
a method of identifying an individual by comparing his/her profile with another known DNA fingerprint.
DNA profiling uses:
- Diagnosis of inherited disorders
- Developing cures for inherited disorders
- Biological evidence (forensic science)
- Identification of relatives
What makes up proteins?
the monomers - amino acids
When amino acids combine, what happens?
water is released —> dehydration synthesis.
- 2 AAs combine = dipeptide
- 3 or more AAs combine = polypeptide.
How many different amino acids are there?
There are only 20 different AAs that make up all proteins (chains of 50 or more AAs)
The significance of the sequence of amino acids?
The sequence in which AAs combine is determined by the sequence of nitrogenous bases in DNA. The order of the AAs determines what protein will be formed.
What are the 3 stages of protein synthesis
- Transcription
- Movement of mRNA out of the nucleus
- Translation
- Transcription – formation of messenger RNA (mRNA)
- DNA double helix unwinds
- Weak H bonds of DNA break —> 2 single strands of DNA (only a portion ‘unzips’)
- One strand acts as a template
- To form a complementary strand (mRNA), using free RNA nucleotides from the nucleoplasm.
- This process is called transcription
- 3 adjacent bases on mRNA make up a codon
Each codon codes for a specific amino acid.
- Movement of mRNA out of the nucleus
- mRNA moves out of the nucleus
- Through the nuclear pore into the cytoplasm
- Where it attaches to a ribosome
- Translation – using information from mRNA to form a protein
- According to the codons of mRNA
tRNA (transfer RNA) molecules with matching/complementary anticodons bring the required amino acids to the ribosome - The AAs link together by a peptide bond to form the required protein
- This process is called translation
