Compendium 11 Flashcards
Describe DNA
Deoxyribonucleic acid
Contain genetic information in nucleus
Approx 23000 genes in human genome - genes are the codes for proteins
Only 1.5% DNA due to genes, 98.5% is non-coding which includes regulatory substances, introns and repeat elements which are needed for regulating genes and protein expression
Describe structure of DNA
Double stranded (helix) Sugar phosphate backbone Complementary nitrogenous bases Adenine - thymine Guanine - cytosine
How is DNA organised
DNA wrapped around proteins called HISTONES
HISTONES and DNA bundled together are called chromatin
Chromatin twists around to make chromosomes (occurs only when cells divides)
How many chromosomes do somatic cells have
Each somatic cell has 2 copies of each chromosome - one inherited from mum, other inherited from dad
What are homologous chromosomes
The maternal and paternal chromosomes of a pair are called homologous chromosomes
And make a homologous pair
Difference between autosomal and sex chromosomes
Humans have 22 pairs of autosomal chromosomes
1 pair of sex chromosomes
Women - 2 X
Men - 1 X 1 Y
What is diploid and haploid
Gametes only have 1 chromosome of each homologous pair (23 chromosomes) so we called HAPLOID
Somatic cells have 46 chromosomes (homologous pairs) and are allied DIPLOID
What is a karotype
When cells divide the chromosomes become easier to see and can be arranged into pairs - this kind of map is karotype
What are genetics
Study of hereditary
What is a gene
Piece of DNA that codes protein
What is an allele
Different forms of the same gene - one inherited from dad, one from mum for every gene
What is a genotype
The actual gene (allele)
What is a phenotype
Persons appearance
What is a locus
Location of gene on a chromosome
What is a proteome
Cells constantly synthesise different proteins needed for cell functions or to be exported
DNA contains instructions to make proteins
Not all cells make all proteins
A proteome of a cell is all the proteins that a cell makes and proteomics is the study of this
Cells make different proteins but all cells contain the same DNA- how they use it and what parts they use is what differs
What is protein synthesis
- Transcription - DNA converted to RNA
- Translation - RNA converted to protein
The flow of DNA to RNA and then protein is called the central dogma
List steps of transcription
1) DNA strand (chromatin) uncoils (only template strand is used)
2) RNA polymerase enzyme (transcription factor) initiates transcription by binding to promoter region on DNA strand
3) polymerase catalyses formation of mRNA chain by using DNA strand as a template (copies info) - called RNA transcript and follows complementary base sequencing (A with U, G with C)
4) mRNA will end at a terminator sequence
5) mRNA exists nucleus through nuclear pores to cytoplasm
How is RNA different to DNA
Sugar: ribose instead of deoxyribose
Single stranded
Contains uracil instead of thymine
RNA acts as an intermediary between DNA and protein
What three types of RNA are transcribed from DNA
1) messenger RNA (mRNA): translated in cytoplasm to make proteins
2) ribosomal RNA (rRNA): together with ribosomal proteins it makes up the ribosomes
3) transfer RNA (tRNA): each tRNA can bind specifically to one of the 20 different amino acids used to build proteins, important in translating mRNA into amino acid peptide
List steps of translation
Occurs in cytoplasm by ribosomes on rough endoplasmic reticulum or free within cytoplasm
1) mRNA carries genetic info from hue clubs to ribosomes
2) the sequence is read by translational machinery in the ribosome, in lots of three nucleotides (a codon)
3) translation starts at codon AUG of each gene in the mRNA - each codon = specific amino acid
4) as each codon is read, a tRNA with a complementary sequence (anticodon) binds to each triplet (the tRNA carries the amino acid specified by the codon)
5 amino acid joined together by peptide bonds in sequence specified by mRNA to make a protein
May then move to Golgi apparatus
Explain codons and amino acids
There are 64 possible codons in mRNA and only 29 naturally occurring amino acids
Some amino acids are specified by only one codon (e.g. Methionine- AUG)
Others specified by up to sex different codons (e.g. Leucine- UUA, UUG, CUU…)
Three codons do not code for an amino acid but signal termination of peptide chain (tRNA chain doesn’t come over)
Stop codons - UAG, UAA, UGA
What is a primary protein structure
Sequence of amino acids linked by peptide bonds
What is a secondary protein sequence
Proteins fold to form secondary structures due to side chains
Two regular folding patterns are seen : alpha helices and beta pleated
What is a tertiary protein structure
The 3D shape determined by folding secondary structure - held together by bonds between amino acids that may be far apart in the actual chain
What is a quaternary protein structure
Combined 3D structure of two or more polypeptide chains e.g. Haemoglobin
What are fibrous and globular protein
Globular: polypeptide chain folds up into compact shape, usually water soluble, mobile, chemically active (most enzymes), play crucial role in nearly all biological process e.g. Haemoglobin
Fibrous: simple, 3D elongated structures, insoluble and stable in water, mechanical support and tensile strength, abundant outside cell often in matrix between cells, e.g. Collagen, keratin, elastin
Describe difference between somatic cells, germ cells and gametes
Somatic: diploid, most body cells, mitosis
Germ cell: give rise to gametes, testes and ovaries, meiosis
Gamete: cells fuse during reproduction, haploid so when speed fertilisers egg the resulting embryo has correct DNA amount
What are the main steps of cell division
Interphase (cells spend most of life)
Mitosis
Cytokinesis (division of cell cytoplasm)
Explain interphase
- g1 phase- normal growth and metabolic activity
- S phase- DNA in each 46 chromosomes is replicated- makes two identical copies of its DNA so during division one copy goes to each daughter cell)
- G2 phase- preparing for division: centrioles divided and doubled, spindle fibres formed that extend from centrioles and organelles and proteins doubled.
List steps of mitosis
- Prophase:
- chromatin condenses into pairs of chromatids called chromosomes which consist of 2 sister chromatids connected by centromere
- centrioles migrate to ends of cell where spindle fibres will attach to centromeres
- nuclear envelope and nucleolus disintegrates - Metaphase
- chromosomes are aligned at nuclear equator - Anaphase
- spindle fibres attached to centromeres separate the chromatids
- 2 identical sets of chromosomes move to separate ends of cell, cytokinesis begins - Telophase
- nuclear envelope reforms around each chromosome set
- chromosomes decondense into chromatin
- cytokinesis continues
Explain meiosis
Germ cells division
Involves 2 cell divisions
Produces 4 genetically different daughter cells (haploid as DNA only replicates once but cell divides twice)
Resulting gametes can unite to form a zygote
List steps of meiosis
Occurs after interphase and DNA replication
- Early prophase I:
- charismatic pairs joined by centromere - Middle prophase I:
- homologous chromosomes begin to line up to form a synapse which causes crosses over and sharing of genetic information from two different chromatid strands - Metaphase I:
- homologous chromosomes (23 pairs) align at cell centre
- random assortment of homologous chromosomes occur - Anaphase I:
- homologous chromosomes move apart to opposite sides of cell caused from pulling of spindle fibres - Telophase I:
- new nuclei from and the cell divides into 2 genetically different daughter cells - Prophase II:
- centrioles at each end with spindle fibre extending
- nuclear envelope disintegrates
- each chromosome consists of 2 chromatids - Metaphase II:
- 23 chromosomes align individually along cell centre - Anaphase II:
- sister chromatids of chromosomes separate and each is now called a chromosome
- achieved by pulling spindle fibres - Telophase II:
- new nuclear envelope form around chromosomes
- cytoplasm begins to separate
- the cell divides to form 4 daughter cells with haploid number of chromosomes
