DNA, RNA and Protein Synthesis Flashcards
1
Q
Homologous Pair
A
2 chromosomes that carry same genes but not necessarily same alleles
2
Q
How is DNA stored in Eukaryotic Cells?
A
- Contain linear DNA molecules that exist as chromosomes (chromosomes are found in the nucleus)- thread like structures, each made up of one long molecule of DNA and its associated proteins
- DNA molecule is really long, so it has to be wound up so it can fit into the nucleus- it’s wound around proteins called histones (which help support DNA)
- DNA and protein is then coiled up very tightly to make a compact chromosome
3
Q
DNA in mitochondria and chloroplasts of eukaryotic cells
A
Similar to prokaryotic DNA beacuse it’s circular and shorter than DNA molecules in the nucleus (not associated with histone proteins)
4
Q
How is DNA stored in Prokaryotic Cells?
A
- DNA molecules are shorter and circular
- DNA isn’t wound around
- Circular chromosome is supercoiled to fit in the cell
5
Q
Genes
A
- DNA contains genes
- A gene is a squence of DNA bases that codes for either a polypeptide or functional RNA
- Sequence of amino acids in a polypeptide forms the primary structure of a protein
6
Q
First stage of protein synthesis (polypeptides)
A
- Different polypeptides have a different number and order of amino acids
- Order of bases in a gene that determines the order of amino acids in a particular polypeptide
- Each amino acid is coded for by a sequence of 3 bases in a gene called a triplet or codon
- To make a polypeptide, DNA is first copied into messenger RNA (mRNA)
7
Q
What do genes code for if they don’t code for a polypeptide?
A
- Functional RNA
- Functional RNA is RNA molecules other than mRNA which perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA which forms part of ribosomes
8
Q
Genome
A
Complete set of genes in a cell
9
Q
Proteome
A
Full range of proteins that the cell is able to produce
10
Q
Non-coding DNA in Eukaryotes
A
- Lot of nuclear DNA doesn’t code for polypeptides
- Some genes don’t code for polypeptides at all- they code for functional RNA
- Even genes that do code for polypeptides contain sections that don’t code for amino acids (Introns)
- There can be several introns within a gene
- Intons in eukaryotes are removed during protein synthesis- so they don’t affect the amino acid order
- Bits of the gene that do code for amino acids are called exons
- Prokaryotic DNA doesn’t have introns
- Eukaryotic DNA contains regions of multiple repeats outside of genes (DNA sequences that repeat over and over)
- These areas don’t code for amino acids either, so they’re called non-coding multiple repeats
11
Q
Alleles
A
- Gene that exists in more than one form
- Order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide
12
Q
Homologous Chromosomes
A
- In a eukaryotic cell nucleus, DNA is stored as chromosomes
- Humans have 23 pairs of chromosomes, 46 in total
- Homologous pairs- pairs of matching chromosomes
- In a homologous pair, both chromosomes are the same size and have the same genes, although they could have different alleles
- Alleles coding for the same characteristic will be found at the same fixed position (locus) on each chromosome in a homologous pair
13
Q
What is protein synthesis?
A
Production of proteins (polypeptides) from the information contained within a cell’s DNA (involves transcription and translation)
14
Q
Transcription definition
A
- Where the DNA code is copied into a molecule called mRNA
- mRNA copy of a gene is made from DNA
- In eukaryotic cells, takes place in the nucleus
- Prokaryotes don’t have a nucleus, so transcription takes place in the cytoplasm
15
Q
Translation definition
A
- In both eukaryotes and prokaryotes, translation occurs at the ribosomes in the cytoplasm
- Amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by mRNA
16
Q
Messenger RNA (mRNA)
A
- Made during transcription
- Carries the genetic code from the DNA to the ribosomes, where it’s used to make a protein during translation
- mRNA is a single polynuceotide strand and groups of 3 adjacent bases are usually called codons (sometimes called triplets or base triplets)
17
Q
Transfer RNA (tRNA)
A
- Involved in translation
- Carries amino acids that are used to make proteins to the ribosomes
- Single polynucleotide stand that’s folded into a clover shape
- Hydrogen bonds between specific base pairs hold the molecule in this shape
- Every tRNA molecule has a specific sequence of 3 bases at one end called an anticodon
- Also has amino acid binding site at the other end
19
Q
Stages of Transcription
A
- RNA polymerase (an enzyme) attaches to the DNA double-helix at the beginning of a gene
- Hydrogen bonds between 2 DNA stands in the gene break, separating the strands
- DNA molecule uncoils at that point, exposing some of the bases
- One of the strands is then used as a template to make an mRNA copy
- RNA polymerase lines up free RNA nucelotides alongside the exposed bases on the template strand
- Free bases are attracted to exposed bases
- Specific, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand (except base T replaced by U in RNA)
- Once RNA nucelotides have paired up with their specific bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA strand
- RNA polymerase moves along the DNA, assembling the mRNA strand. Hydrogen bonds between uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix
- When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from DNA
- In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place
22
Q
Translation
A
- mRNA attaches itself to a ribosome and transfer RNA molecules carry amino acids to it
- ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form
- tRNA molecule carrying an amino acid, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing
- Second tRNA molecule attaches itself to the next codon on the mRNA in the same way
- 2 amino acids attached to the tRNA molecules are joined by a peptide bond
- First tRNA molecule moves away, leaving its amino acid behind
- Third tRNA molecule binds to the next codon on the mRNA
- Amino acid binds to the first two and the second tRNA molecule moves away
- This process continues, producing a chain of linked amino acids until there’s a stop signal on the mRNA molecule
- Polypeptide chain then moves away from the ribosome and translation is complete
