DNA and Polypeptide Synthesis Flashcards
Prokaryotic
Prokaryotic cells:
- no nucleus
- 1-5um
- free moving in the cytoplasm - in the nucleic region (nucleiod)
- no membrane bound organelle
- only unicellular life
- archaebacteria, eubacteria
Eukaryotic cells
- true nucleus
- 10-100um
- contained within a membrane bound nucleus
- membrane bound compartments such as nucleus and mitochondria
- yes (most multicellular life, exception of protists)
- animal, plants, protists and fungi
Prokaryotic DNA
Info:
Contains a single chromosome, circular strand of DNA with no membrane and free in the cytoplasm
- Circular DNA can supercoil and form a loop around a centra dense protein (scaffold) to form a nucleoid
- Non-chromosomal DNA = plasmids
Location: DNA is free moving in the cytoplasm, no membrane (nucleoid region)
Protein binding: circular DNA can supercoil and form loop around a central dense protein (called the scaffold) to form a nucleoid
Genomes are compact (contain little repetitive DNA and no introns)
Contains plasmids
Is circular in shape
Plasmids:
- Small rings floating separately in the cytoplasm
- Replicate independently of chromosome
- Codes for non-essential features but for those providing a selective advantage (antibiotic resistance)
Eukaryotic DNA
Info:
- DNA in a membrane bound nucleus
- Individual DNA molecules are arranged into separated chromosomes
- Introns are a large proportion of non-coding DNA
- Linear, double helix DNA shape
- DNA wrapped around histones which coil up to make chromosomes
- Non-nuclear DNA is not contained within the nucleus, includes mt DNA
Location:
Conatined within a membrane bound nucleus
Protein binding: is bound to histone proteins
Genomes: genomes contain large amounts of non-coding and repetitive DNA (including introns)
Contains plasmids: do not contain plasmids (but organelles such as the mitochondria)
Shape: linear - double helix
Non-chromosomal: Codes for coding proteins for respiration
- Mitochondrial DNA (mt DNA) is found in the respiratory organs of cells – can be used to trace maternal inheritance
- Mt DNA is very small (70nm), circular, double stranded, contains no introns, with only 37 genes (13 for respiration functions, 24 for RNA molecules)
- Each cell has 100-1000 mitochondria, and each contains 5-10 circular DNA molecules
Protein synthesis: DNA
DNA
Structure Double stranded molecule
Nitrogenous bases of adenine, thymine, cytosine and guanine
Location Inside nucleus
Small amount found in mitochondria and chloroplast
Role Chemical code (info) used in protein synthesis and responsible for transmitting inherited from one cell to another during cell division.
Protein synthesis: RNA
Single stranded molecule
Uracil replaces thymine
Small amount in nucleus large amount found in cytoplasm
Used in the process of protein synthesis.
Includes: Messenger RNA (mRNA), Transfer RNA (tRNA), ribosomal RNA (rRNA)
amino acid
Amino acid: a simple organic compound containing a carboxyl and amino group – building blocks of protein
peptide:
short chains of 2-50 amino acids
polypeptide:
linear molecules made of multiple peptides
protein
the functional unit, made up of one or more polypeptides
transcription
the process by which a complementary copy (mRNA) or a gene (DNA) is made in the nucleus
translation
the process by which mRNA sequence is converetd into a specific sequence of amino acids (carried by tRNA) in the ribosomes (changing language from nucleotides to AAs)
mRNA
messenger ribonucleic acid, single stranded nucleic acid, consisting of ribose sugar, phosphate backbone and nitrogen bases (AUGC)
tRNA
transfer ribonucleic acid, small RNA molecule that transfers specific amino acids to the ribosome during formation of polypeptides
codon
set of three nitrogen bases in mRNA
anti-codon
complementary set of three nitrogen bases on tRNA
process of transcription
- DNA cannot leave the nucleus (as it is too large to pass through the pores)
- DNA polymerase binds to a section of the DNA called the ‘promoter’
- A short section of DNA unzips (the hydrogen bonds break between the 2 strands)
- Section revealed is the DNA containing genetic info to make a protein – called non-coding / sense strand (the section not used is the coding/antisense strand)
- DNA polymerase uses non-coding/sense strand as a template to build mRNA (where uracil replaces thymine)
- Transcribed mRNA exits cell through the nuclear pore
Process of translation
- Occurs in the ribosomes of the cells (found within the RER in cytoplasm)
- Single stranded mRNA molecule exits nucleus via nuclear pore, finding and attaching to a ribosome
- tRNA attaches temporarily to mRNA by pairing tRNA anti-codons with complementary codons (mRNA triplets of bases)
- amino acids (attached to tRNA tail) are attached together assisted by enzymes to form a polypeptide chain
- each amino acid is then spliced off its tRNA carrier
- tRNA goes off to collect more amino acids which are floating in the cytoplasm
total overview
- DNA is transcribed into RNA
- mRNA attaches to a ribosome
- amino acid attaches to tRNA
- more amino acids are added
- tRNA breaks off and picks up another amino acid
genotype
set of genes in the DNA responsible for a particular phenotypic trait
phenotype
the physical expression of that trait as a protein or physically observable characteristic
alleles
different forms of the same gene
gene expression
switching on and off genes as needed
how gene expression is controlled:
- making more/less of a protein or even using the same gene to make several different proteins
1. controlling the degree of packaging of the DNA around histones (also called epigenetics)
2. use of regulator proteins (also called transcription factors in eukaryotes)
3. RNA processing control (also called post-transcriptional modification) - how the mrna is modified
- removing introns
- adding protective caps and tails
Packaging around histones
• Repression of genes (switching off)
- Through methylation (methyl groups attach to DNA to increase the binding of DNA to the histones)
- Tightens the binding to histones which means DNA can’t be accessed by transcription factors – DNA polymerase cannot get to the promoter region
• Activation (switching on)
- Through acetylation (acetyl groups weaken the binding of DNA and histone proteins)
- Loosening the binding means DNA polymerase more easily accesses promoter region
Use of regulator proteins (also called transcription factors in eukaryotes)
- RNA polymerase binds to the DNA at the start of the gene to start transcribing it
- The bit at the start of the gene is called the promoter region
- Regulator genes make regulator proteins (either repressors or activators)
- These either prevent RNA polymerase from transcribing the gene or help it bind to the start of the gene (thus help transcribe it)
Gene expression through RNAN processing gene regulation
• DNA contains:
- Exons coding segments, expressed as proteins
- Introns non coding segments, not expressed, does not produce proteins (lots of our DNA is made up of introns but they have no function, the yare like evolutionary relics of genes that we no longer express)
• Straight after transcription spliceosome enzyme removes the introns to form pre-mRNA
- Cutting them out prevents random amino acids from attaching to the polypeptide chain
- Alternative splicing: the exons can be assembled into a mature mRNA (which goes off for translation) is slightly different orders each time = increased range of proteins can be produced in complex organisms
Primary structure
- Amino acid sequence
- The order of amino acids gives the polypeptide its primary structure
- 60 triplet codes code for the 20 different amino acids
- Forms chains of up to 300 amino acids
- Amino acids are held together by peptide bones
Secondary structure:
hydrogen bonding of the peptide backbone
results in folding of the amino acids into a repeating pattern
Tertiary protein structure
- 3D folding pattern of a protein due to side chain interactions
- structure of the polypeptide chain
quaternary protein structure
- protein consisting of more than one amino acid chain (several polypeptide chains)
assessing the effect of genes and environment on phenotype
I: the phenotype is the physical expression of a trait, as a protein or physically observable characteristic
D: the phenotype is determined by the genotype and can be influenced by the environment, depending on the gene in question. For example, blood type if determined by the genotype, while height and weight is influenced by both genotype and environment.
E/A: in conclusion, the genotype always plays a role in determining the phenotype while the environment also influences the expression of many genes.
