DNA , GENES , PS Flashcards
Gene
Section of DNA on a chromosome that codes for the sequence of amino acids in a polypeptide and functional RNA
What to genes determine ?
Nature and development of all organsisms
The gene is a base sequence of DNA that codes for :
- amino acid sequence of a polypeptide
- functional RNA
How many amino acids in protein
20
Each amino acid has
Own code of bases on the DNA
What combo die scientists agree on ?
4^3 = 64 codes
Triplet
3 bases on strand of DNA
Codon
Bases for RNA
Features of genetic code : degenerate
More than one amino acid can code for one base sequence
Features of genetic code : Way they’re read
Each triplet code is read in same direction (5’ to 3’)
Features of genetic code : Stop codes
3 triplets code for no amino acids which leads to stop codes so its the end of the gene
Features of genetic code : Non overlapping
Each code is only read once
Features of genetic code : Universal
Each triplet codes for same amino acid in every organism
Why is the genetic code degenerate but not ambiguous
Multiple triplet codes for amino acids but these same triplets will alway code for same amino acids
Exons
Coding sequences of bases
How are introns removed
- splicing
- removed from pre messenger RNA after transcription
Eukaryotic DNA vs prokaryotic DNA
- Very long (e)-short (p)
- linear(e)-ring structure(p)
- chromosomes(e)-no chromosomes(p)
- associated with proteins/histones (e)-not associated with proteins(p)
Mitochondrial DNA and chloroplast DNA
Same as prokaryotic
Chromosome structure : Chromatin
Within the nucleus of resting phase (interphase) DNA exists in form of chromatin
Chromosome structure : Sister chromatids
2 daughter strands connected by a centromere
Chromosome structure : Why is each thread called a chromatid
DNA has replicated to give 2 identical molecules
Chromosome structure : What is DNA in chromosomes held by and what is the function of protein in chromosomes
Histones
- fix dna into position
Chromosome structure : Length of DNA in each cell
- 2m in every human cell
- highly coiled an folded
Chromosome structure : What does a chromosomes contain
Single molecule of DNA which has many genes along it
- each gene has a locus (specific position ) along the DNA molecule
Locus
Location of gene on the strand of DNA / chromosome
Chromosome structure : what happens after helix I wound around histones
- dna-histone complex coiled and looped to be packaged into a chromosome
Homologous chromosomes : what are they ?
- pair of chromosomes
- one maternal and one paternal
- Same gene loci which determines the same features
Homologous chromosomes : same genes but not
Same alleles of the genes
Homologous chromosomes : total diploid number
46
Homologous chromosomes : diploid
Nucleus contains 2 sets of chromosomes
Homologous chromosomes : haploid
Cells that only contain a single copy of each chromosome
Karyotyping
Way to analyse chromosomes
Alleles : what is an allele ?
Alternative forms of a gene
Alleles : What happens when alleles are different ?
Each allele has different base sequence so they have a different amino acid sequence = different polypeptide
Alleles : Changes to base sequence of a gene =
- Production of new allele of that gene (mutation) so results in a different sequence of amino acids
- different amino acids = different polypeptide = different protein
Alleles : What happens when proteins change shape
- function damaged because new shape is not complimentary which can have serious consequences on an organism
RNA
Ribonuceic acid
RNA : where does synthesis of proteins occur
cytoplasm
RNA : what are sections of DNA transcribed onto
transcribed onto a single stranded molecule of RNA
RNA : RNA triplet
codon
RNA : DNA vs RNA
double stranded helix - single stranded
longer - shorter
ATCG-AUCG
deoxyribose sugar - ribose sugar
genome
complete set of genes in a cell
Complete Proteome
Full range of proteins produced by a genome
RNA
- polymer made of repeating mononucleotide sub units
- pentose sugar ribose
- bases = AUCG
- phosphate
mRNA
- long strand arranged in a single helix
- mRNA leaves the nucleus via pores in the nuclear envelope where it associates with ribosomes
How is mRNA adapted
- acts as a template for protein synthesis
- possessed information in the form of codons which determines the amino acid sequence of a a specific polypeptide
tRNA
- small molecule
- folded into a cloverleaf shape
- bind to specific amino acid with an anticodon specific to that amino acid
What happens to an anticodon during protein synthesis
Pairs with 3 complimentary organic bases that make up the codon on mRNA
Transcription
Complementary section is made from a molecule called pre-mRNA
Translation
mRNA used as a template so complimentary tRNA attach to amino acids to form a polypeptide
tRNA vs mRNA
Base pairing - no base pairing Cloverleaf - linear AA binding side - no AA binding site Standard/shorter- longer Few(64)-many kinds More stable due to H bonds - less stable
Transcription : steps
- DNA strands in the nucleus are separated by breaking H bonds
- DNA helicase (enzyme) used and template strand produced
- Free RNA nucleotides attracted to exposed DNA bases
- RNA nucleotides undergo complimentary base pairing
- Adjacent RNA nucleotides are joined by RNA polymerase
- Pre-mRNA formed and splicing of pre-mRNA removes introns to form mRNA
Prokaryotic DNA
Doesn’t have introns
Translation : steps
- mRNA attaches to ribose
- Ribose moves along to a start codon
- tRNA carry specific amino acids to mRNA
- Anticodon , of tRNA,binds to complimentary mRNA
- Ribosomes moves to next codon
- Process repeats and amino acids are joined by peptide bonds via condensation reaction
Meiosis
Type of nuclear division where number of chromosomes is halved
What type of cells are meiosis for
Reproductive
Testes / ovaries
IPMAT in meiosis
Interphase Prophase Metaphase Anaphase Telophase (cytokinesis) PMAT repeated
Meiosis : interphase
- diploid
- growth and DNA replication
- sister chromatids form and are held together by the centromere
Meiosis : prophase 1
- homologous chromosomes pair up randomly ( independent assortment/segregation )
- crossing over which form chiasmatas and they recombine
- allele exchange introduces variation and spindle fibres form
- nucleus breaks down
Meiosis : metaphase 1
- spindle fibres line up bivalents along the middle
Meiosis : anaphase 1
- spindle fibres contract and separate bivalents to opposite sides
Meiosis : telophase 1 + cytokinesis 1
- 2 nuclei (telophase)
- cell membrane and cytoplasm divide
- 2 daughter cells
- diploid to haploid
Meiosis : prophase 2
- nucleus breaks down and spindles form
Meiosis : metaphase 2
- chromosomes line up in the middle
Meiosis : anaphase 2
Sister chromatids separated at centromere
Meiosis : telophase 2
- new nuclei forms
Meiosis : cytokinesis 2
4 unique gametes formed
Meiosis : what causes genetic variation
- independent assortment and choosing over to form chiasmatas
Advantages of dna being stable
- passed generation to generation without damage which maintains similarity between parents
- mutations can be harmful
Advantage of mRNA being easily broken down
- only needed at certain times so only used and made when needed
