DNA - protein synthesis - cell division - stem cells Flashcards
dna function
control cell activity
codes for proteins
where is dna found
eukaryotes: the nucleus
prokaryotes: the cytoplasm (plasmid DNA, nucleoid)
nucleic acid
polymers of nucleotides
nucleotide
monomer of nucleic acids
pentode sugar deoxyribose, a phosphate group, and a nitrogenous base
bases
5 types G C A T - only in DNA U - only in RNA (G-C, A-T/U)
triplet code
3 bases code for 1 amino acid
gene
a short section of DNA that codes for a protein
RNA
another nucleic acid different to DNA: - shorter - single stranded - found outside the nucleus
why can’t genes leave nucleus
molecule is too big to leave the nucleo pores
so it’s copied and the copy goes to the ribosome where proteins are assembled
steps in protein synthesis
- Transcription - copy gene
2. Translation - ‘translate’ mRNA code into amino acids
transcription
in the nucleus
- gene is UNZIPPED temporarily
- mRNA reads and PAIRS complementary bases (U not T) of each nucleotide of the template strand (DNA)
- mRNA can LEAVE the nucleus through the nucleo pores - short, single stranded
translation
on ribosomes
3 nucleotides > 1 amino acid
- mRNA leaves nucleus and ATTACHES to ribosome in the cytoplasm
- tRNA brings a SPECIFIC AMINO ACID according to the triplet code on the mRNA
- base pairs on tRNA are complementary to mRNA so tRNA ATTACHES TO mRNA on ribosome
- a second specific amino acid is carried to the ribosome
- the second tRNA attaches to its complementary sequence on the mRNA
- a PEPTIDE BOND forms between 2 amino acids
- the first tRNA LEAVES
- a POLYPEPTIDE CHAIN grows on the ribosome as the message is read and more amino acids are carried
4 bases code for
20 amino acids which code for
all proteins
mRNA
messenger RNA carries instructions from DNA in the nucleus to the ribosome made in nucleus short single stranded contains U not T
tRNA
transfer RNA
carries amino acids to the ribosome
why do cells divide
growth, repair, replacement
- a type of asexual reproduction - makes genetically identical offspring
cell division
- cell GROWS + number of organelles increases
- DNA in chromosome REPLICATES
- further growth and DNA is CHECKED for errors
- MITOSIS - chromosomes move apart + 2 nuclei form
- cytoplasm DIVIDES in two and the new cell membrane separates off to give 2 new identical cells
DNA replication
DNA is copied before division to ensure cells contain the same genetic info
- double helix UNZIPS to form 2 strands
- new bases line up using COMPLEMENTARY base pairing (A-T, C-G)
- 2 identical strands are made
mitosis
- prophase- spindle fibres extend
- metaphase - chromosomes line up in the middle
- anaphase - chromatids pulled apart to opposite poles
- telophase - 2 nuclei form
prophase
FIRST STAGE
Chromosomes become visible
nuclear membrane dissolves
spindle fibers extend
metaphase
Chromosomes line up in the middle of the cell
anaphase
chromosome separates as spindle fibers pull them apart to opposite poles
telophase
FINAL STAGE
After the chromosome seperates, the cell seals off
2 nuclei form
interphase
period of the cell cycle between cell divisions
how many pairs of chromosomes humans have
23 pairs = 46 total
diploid
contains two sets of chromosomes (1 from mum, 1 from dad)
why mitosis
ensures each daughter cell is genetically identical to its parent cell (so each cell can carry out its specialised function)
stem cells
cells that haven’t become specialised (undergone differentiation)
can turn into many different cell types
types of stem cells
embryonic
adult
embryonic stem cells
found in embryos (blastocyst)
can develop into almost any cell type
adult stem cells
found in adult tissues (e.g. bone marrow)
can only become a few cell types (e.g. blood cells (red/white))
uses of stem cells
- repair - replace damaged or diseased cells
- growth - make new cells
- research - can help leukaemia, diabetes, alzheimer’s, cancers
why dont all cells divide
some cells have such a unique adaptation and function (such as nerve cells) with complicated structure and pathways so division would disrupt this
- cells whose function is determined do no undergo mitosis
why use your own stem cells
your body’s immune systems may attack the donor cells and REJECT them
